Cultural Evolution: Theory, Review, and Prospectus

Since the Lahti Lab’s founding in 2009, collectively we have done more work in cultural evolution than any other research area. Cultural evolution is the change in socially learned traits as they are transmitted from one individual to another. Analogous to genetic evolution, this process results in varying traditions, divergence of traits in different social groups, and sometimes sequential improvements that we could call technology. Although much of our research is directly empirical, using bird song or human traits as case studies, we also commonly engage in assessments of the process or the disciplinary field that studies it—that is, theory, review, and prospectus.

We have developed three exploratory models of cultural behavior in collaboration with several other researchers: one that uses coalescent theory to work backwards along a cultural trait’s ancestry in an effort to determine its origin^11,12; one of cultural “systems” where traits are not viewed independently but rather as components of an interactive whole that that involve varying degrees of mutual compatibility^5,11; and a novel method of measuring behavioral synchrony, where organisms influence each other’s behavioral timing¹¹. We have produced other cultural evolutionary models but these are data-driven and so will be covered in other projects.

We have completed six reviews of behavioral phenomena relevant to cultural evolution. Four of these relate explicitly to birds: three summaries (two cursory and one more detailed) on the similarities between bird song and human language with respect to both vocal learning and speech^8,14,15, and a thorough investigation of the role that constraints on individual performance abilities play in the evolutionary trajectories of bird songs¹³. We have also reviewed the evidence for cultural behaviors specifically in nonhuman mammals¹⁰, as social learning is far more common and less controversial than culture. Likewise we assessed the evidence for teaching in nonhuman animals⁷; social learning is much more common and easier to document than teaching, where an individual changes its behavior specifically for the function of another’s learning. In a nutshell, the results of these last two reviews are that animal cultures are uncommon but increasingly being found, but they are very simple in terms of the numbers of cultural steps that have been taken; and teaching is present in animals but rare, although it is likely more common than we think because of the practical difficulty of identifying it.

Cultural evolution as a research area is relatively young and eclectic. This means that it could benefit from some improvements in conceptual clarity, and integration among the disciplines that investigate it. When we realized this issue and proposed some solutions to a granting organization, the professional cultural evolutionist reviewers were defensive: we’re doing just fine! So we set out to prove our point, the first product of which was a bibliometric analysis of the cultural evolutionary literature^6,9. Based on over 2091 works published by 3451 authors in 67 countries, we examined the degree to which researchers cite each other and collaborate. Our results indicate a vibrant and growing field that is somewhat fractured into subdisciplines, but is increasing in interaction over time.

Currently our lab is engaged in three specific ventures that seek to increase conceptual clarity and ensure that research in the field is not based on inconsistent or presumptuous first principles. First, the phenomenon of “cumulative cultural evolution”, where traits not only change but demonstrably improve over time across individuals, has always been a thorny topic and difficult to pin down. We focus on this notion applied to bird song: if a male song changes over the generations to become more attractive to females or threatening to males, has it improved? For several reasons we suggest avoiding the term “cumulative cultural evolution” in such cases^1,4. Second, rarely have empirical studies considered how fast cultural evolution occurs and what factors determine that rate, which we call “cultural lability”. We use bird song as arguably the best model system for studying cultural lability, and find that existing evidence indicates various demographic and ecological features as modulators of it^1,3. Third, focusing as cultural evolution does on transmission, it has a prima facie origination problem—if we talk only about transmission of an idea from one individual to another, how do we explain new ideas arising in the first place?² Our goal is to ensure that cultural evolution begin to take this matter seriously, but in such a way that does not prejudge the nature of the imagination or the mechanism by which innovation is generated in the mind, as a wide range of empirically valid perspectives are held on such matters.

1. Geller, Frances C. (in prep). [Cultural Evolution of Bird Song]. PhD dissertation.
2. David C. Lahti & Jonathan Goodman (in prep). Human innovation and cultural evolution.
3. Geller, Frances C. & David C. Lahti (in prep). Cultural lability: Insights from bird song.
4. Geller, Frances C. & David C. Lahti (in press). Is sexiness cumulative? Arguments from birdsong culture.
5. *Jansson, Fredrik, Elliot Aguilar, Alberto Acerbi, & Magnus Enquist. 2021 Modelling cultural systems and selective filters. Philosophical Transactions of the Royal Society B: Biological Sciences 376:1828. DOI:10.1098/rstb.2020.0045.
6. Youngblood, Mason. 2021. From Psychology to Phylogeny: Bridging Levels of Analysis in Cultural Evolution. PhD dissertation, City University of New York, Doctoral Program in Psychology. New York, NY. 202 + xxviii pp.
7. Morales, Cristina. 2020. A review of teaching in human and nonhuman animals. Master’s Literature Review, Department of Biology, Queens College, City University of New York. 28 pp.
8. Mann, Daniel C. Stabilizing Forces in Acoustic Cultural Evolution: Comparing Humans and Birds. PhD dissertation, City University of New York, Doctoral Program in Linguistics. New York, NY. 206 + xvi pp.
9. *Youngblood, Mason P. and David C. Lahti. 2018. A bibliometric analysis of the interdisciplinary field of cultural evolution. Palgrave Communications 4:120, 1-9.
10. Van Deurs, Christian. Nonhuman mammalian cultural behaviors and the animal cultures debate. Master’s Literature Review. Department of Biology, Queens College, City University of New York. 37 pp.
11. Aguilar, Elliot. 2016. Models and Methods in Cultural and Social Evolution. PhD Dissertation, City University of New York, Doctoral Program in Biology, Subprogram in Ecology, Evolution and Behavior. New York, NY. 145 + xviii pp.
12. *Aguilar, Elliot and Stefano Ghirlanda. 2015. Modeling the genealogy of a cultural trait. Theoretical Population Biology 101:1-8.
13. ^*Podos, Jeff, David C. Lahti, & Dana L. Moseley. 2009. Performance limits and birdsong evolution. Advances in the Study of Behavior 40:159-195.
14. ^Lahti, David C. 2007. Birdsong and human speech. In M. Bekoff (ed.), Encyclopedia of Human-Animal Relationships. Westport, CT: Greenwood Publishing Group.
15. ^Lahti, David C. 2007. Similarities in vocal learning between animals and humans. In B. Bekoff (ed.), Encyclopedia of Human-Animal Relationships. Westport, CT: Greenwood Publishing Group.

See also:
Cultural Evolution of Human Language, Music, and Ideas
Cultural Evolution of House Finch Song

Natural History and Urban Ecology of the New York Metropolitan Area

Since 2019, the most productive new research area in our lab is the Bronx River Urban Ecology Project. This is a collaboration with the laboratory of Dr. Bobby Habig at Mercy College; Bobby founded the project while he was a postdoctoral researcher in our lab. The goal of this project is to conduct assessments of biodiversity along New York City’s only freshwater waterway, the Bronx River, with each of several researchers focusing on a particular group of organisms. With up to 18 sampling stations established along the river and with detailed information about the surrounding landscape, we are documenting differences in biodiversity along the 37 km of the river’s length, and inferring ecological influences. Also, by replicating the methods of past surveys, we are able to place our results in historical perspective and determine the temporal trajectory of the river’s ecological health across decades. So far we have conducted surveys of birds^6,8, mammals¹, and aquatic macroinvertebrates, which in turn indicate water quality^2,3,7. Assessments are currently underway of plants, macrofungi, and fungal eDNA. Among our results are that more human-altered areas (even if green, such as golf courses or lawns) have lower diversity and more urban-adapted species of birds and mammals. Natural green spaces are particularly important for Neotropical migrant birds. Water quality variation indicates the detrimental effects of combined sewage overflows and municipal stormwater systems. The invasive Asian clam (Corbicula fluminea) has recently made its way into the river; whereas mayflies (Ephemeroptera), a sensitive indicator group, may be disappearing from the river. Despite recent management efforts to rejuvenate the health of the Bronx River, water quality and biodiversity have only slightly improved over the last twenty years.

In parallel with the Bronx River project, we have been performing a more extensive study of mammal diversity across 31 greenspaces in the New York Metropolitan Area^4,5. In addition to the general survey, we are focusing more specifically on abundance and patterns of occupancy of coyotes, which have recently spread into the area, and free-ranging cats. We are conducting these studies in collaboration with the Gotham Coyote Project and researchers at Mianus River Gorge and the American Museum of Natural History. Our conclusions so far are that diversity is higher in larger patches, those that are less human-altered, and those surrounded by less development. Lower human population densities appear to foster a higher diversity of carnivores in particular. Bridges and waterways appear to be barriers to mammal dispersal, as mammal diversity was higher on the mainland (Bronx and Westchester) than on Long Island. The data for coyotes generally follow these trends, although their occupancy patterns might indicate a dependence on human food waste. Cats were less likely to be found in areas frequented by coyotes.

A study of oyster abundance in relation to substrate and water features on Roosevelt Island is also nearly complete, but is currently on the back burner.

1. Nath, Ritika. (in prep). Mammal diversity and land use along the Bronx River. Master’s thesis.
2. *Mahmud, Maleha, David C. Lahti, & Bobby Habig. (in review). The impact of land use and human population density on benthic macroinvertebrate diversity in a highly urbanized river.
3. *Mahmud, Maleha, David C. Lahti, & Bobby Habig. 2023. A longitudinal assessment of benthic macroinvertebrate diversity and water quality along the Bronx River. Northeastern Naturalist 29:415-440. DOI:10.1656/045.029.0403.
4. *Bradfield, Angelinna A., Christopher M. Nagy, Mark Weckel, David C. Lahti, & Bobby Habig. 2022. Predictors of mammalian diversity in the New York metropolitan area. Frontiers in Ecology & Evolution 10:903211. DOI:10.3389/fevo.2022.903211 (17+8pp.).
5. Bradfield, Angelinna. 2022. Predictors of mammalian diversity and coyote and free-ranging cat distribution in the New York metropolitan area. Master’s Thesis, Department of Biology, Queens College, City University of New York.
6. *Goldstein, Amanda J., David C. Lahti, & Bobby Habig. 2022. Avian diversity and land use along the Bronx River. Urban Naturalist 50 (22 pp.).
7. Mahmud, Maleha. 2021. A longitudinal assessment of benthic macroinvertebrate diversity and water quality along the Bronx River. Master’s Thesis, Department of Biology, Queens College, City University of New York. 64 pp.
8. Goldstein, Amanda. 2021. Predictors of avian diversity along the Bronx River. Master’s Thesis, Department of Biology, Queens College, City University of New York. 66 pp.

Cultural Evolution of House Finch Song

Our lab’s main empirical model system for the study of cultural evolution is the song of the house finch (Haemorhous mexicanus). This is an excellent model system because of the song’s high complexity and variation, the abundance of the bird and its readiness to sing, its broad geographical range (across most of North America), its introduction history that invites comparison of ancestral and introduced ranges, and the abundance of historical song recordings from various geographical areas that allow for detailed comparisons across time and space. Our lab has recorded house finches extensively in New York, California, and Hawaii. Our studies of cultural evolution of song in the former two areas were made possible by recordings made in the same locations several decades ago by our late collaborator and Queens College colleague Dr. Paul Mundinger.

Our main questions are of three sorts: What is the mechanism by which new song variants are introduced into a population? How does song change through time and why? And how does song vary across geography and why? We discovered early that the answers to some of our questions differ from place to place and from time to time. Thus we study house finch song in multiple geographical areas and over different time periods, in order assess the historical, demographic, and ecological differences that might have resulted in the variation in our results. Another of our realizations is that neither old-school subjective categorizations of song nor automated quantitative methods are as effective as we would like at distinguishing between songs. Thus we use a combination of methods with differing assumptions and strengths, and have developed two new measures of song complexity: frequency-time excursion and concavity¹³.

Origins of song variation

Taking our three sorts of questions in order, the first—regarding the mechanism by which new song variants appear—is the one about which we know the least. One route we have begun to take into this question is to determine the smallest unit of song change, the fundamental element of cultural evolution so to speak. This can be assessed between-individual (comparing the same song sung by near neighbors or parents and offspring), or within-individual (comparing different renditions of the same song by the same bird). Since house finch songs consist of several seconds of discrete syllables sung in sequence, we can assess song similarity by syllable sequence alignment, similar to base pair sequence alignment in genetic studies.¹⁴ So far we are still at the pilot study level with such investigations.

Another route into the question of how song variation arises is to look for the learned and genetically inherited factors that govern song development. So far we have conducted two studies of this sort. In a hand-rearing and cross-fostering experiment we found that house finch syllable diversity develops via a combination of genetic and learned influences^8,11. A young house finch can be trained by a canary to trill (repeat the same syllable, which they do not do in nature) but only to a point: the cross-fostered house finch delivers a shorter trill than its canary model does, and with less stereotypy. House finches also have inherited predispositions to sing different syllables and thus can do so even without training; however, training enables them to increase their syllable repertoire. The second study illustrated the importance of taking genetics into account in another way. Although birdsong aficionados had known that female house finches sing, our study not only documented this phenomenon for the first time but also showed that there were similarities and differences between the sexes⁷. Females could sing songs as long and complex as those of males, but females sang less often, and at a higher pitch and narrower frequency bandwidth. These differences meant that our studies of cultural evolution would have to take sex into account. 

Temporal changes (allochronic studies)

The second major question we have been asking is how and why song changes through time. We have embarked on longitudinal studies in two locations so far—New York and California—to address this question. The California population is a longstanding, stable population near the geographical origin of the species. In the 1940s this population was also the source for an introduction of the species to southern Long Island, New York. The introduced population spread, gradually at first, but eventually it covered the entire eastern half of the United States, overlapping with the ancestral population in the West. Paul Mundinger had recorded house finch songs in both states, and we took advantage of this situation to record new songs in the in the same locations in order to determine how they had changed over time. In New York, between the early 1970s and 2012, our results can be parsed into eight points^9,10,13:

1. All the main features of house finch song in 2012 (such as song length, pitch, and syntax) are within the same range as they were in 1975.
2. Roughly half of the individual syllables that were around in 1975 were around in 2012, too. The more common the syllables were in 1975, the more likely they were to still be in use by 2012.
3. However, none of the whole songs (that is, sequences of syllables) that we recorded in 1975 were sung by any bird in 2012.
4. The population of songs was more diverse (there were more different syllables in use) in 2012 than there were in 1975.
5. Although birds shared songs with each other in 1975, the birds in our 2012 sample didn’t share any songs with each other, despite being the same distances from their neighbors.

These results were all to be expected. Increased diversity of syllables indicated that any “cultural founder effect” resulting from the limited number of syllables in a small introduced population was becoming ameliorated by population growth and four decades of innovation; and the more syllables there are available, the less neighbors’ songs will resemble each other. The last three results are more intriguing:

6. Birds in 2012 did not repeat their songs as reliably as they did in 1975—they are more likely to skip syllables, add new ones, or switch them around.
7. Individual songs in 2012 had fewer different kinds of syllables than they did in 1975 (despite there being more total syllable types in use in the population as a whole!).
8. In 2012, the syllables that were more common tend to be the ones that are more complex—they change pitch more rapidly and more often. They also tend to be higher pitched. This was not the case in 1975.

Why has the learning program loosened up (#6)? Is this a mechanism analogous to the evolution of evolvability in genetic systems, such that greater permissiveness increases song variation and thus can accelerate response to, say, song preference by females? The results in #8 are consistent with results in this and other species that indicate female preference for complex male songs, and adjustment of song in response to urban noise, which would have increased dramatically in the interim. The fact that individual songs had fewer syllables (#7) might highlight the fact that the increase in complexity was at the syllable level, not the whole-song level; when a bird increases the complexity of syllables in a song but perhaps has a static time or modulation constraint on what qualifies as a whole song, a smaller collection of syllables meets those requirements. These interpretive hypotheses are speculative; focused female choice or male competition experiments on song would be required to test them.

We then extended the New York temporal study by adding a set of 2019 recordings and estimating what transmission biases were involved in the changes that occurred from 1975 to 2012 to 2019^5,6. First we simulated cultural transmission given parameter values associated with various biases (e.g. content bias, frequency bias, and demonstrator bias). In other words, whether a bird tends to learn variants of a certain sort, variants it encounters more or less often, or variants sung by particular individuals, leaves a trace on the way cultural evolution proceeds. Using Bayesian computation and machine learning, we found evidence that the pattern of cultural evolution we observed in house finch song across the three time periods bears the hallmark of content bias—a preference for syllables of a certain sort, apparently more complex ones. Moreover, based on the turnover rate of syllables through time, we estimated transmission fidelity between model and learner to be very high. Thus a generative inference method with another time point maintained and extended a main result that house finch songs have been increasing in syllable complexity. If this is happening during transmission, individuals are choosing more complex syllables to learn from the pool available to them; however, another possibility, perhaps less plausible, is that individuals are enhancing the complexity of syllables they learn.

Our other temporal study is in California, and is ongoing, based on a comparison of one set of recordings Dr. Mundinger made in 1982 and another we made in 2012 in the same locations, throughout the southern half of the state.² This project will not only function as a replicate of the New York study but might highlight differences between cultural evolution in an ancient stable population as compared with a recent introduced population.

Spatial variation (synchronic studies)

Another way to look at cultural evolution besides the explicitly temporal, or allochronic, is to look at geographic variation, as a synchronic (same-time) result of cultural evolutionary changes. This is analogous to studying language evolution not by comparing old and new literature in the same language, but comparing how people at one time speak or write differently in different places. We have conducted such studies in New York, California, and Hawaii. The background for such studies is the concept of a dialect, or a stepwise change in a trait along a geographical transect. Previously song dialects were reported for the introduced New York house finches, but spatial variation of song in the ancestral Californian population was considered a cline, or continuous decline in similarity over distance. The third possibility is stochastic variation, where there is no relationship between distance and song similarity.

In New York, songs of 96 individuals recorded in 2012 in a 34×40 km area of western Long Island were compared with each other and the similarity of songs and their component syllables were related to the distance between the individuals.¹³ The result was consistent neither with dialects nor a cline, but somewhere between them—over the decades apparently dialects had softened into blending “clouds” of variation. Nearby birds had higher syllable sharing than more distant individuals, up to about 12 km distance, beyond which variation was stochastic. In addition, there were modest regional differences, where features related to minimum frequency, frequency change (concavity) and the duration of silent intervals were related to where individuals were recorded across the area.

Results from a parallel assessment of Californian songs, also recorded during 2012, yielded similar results to the New York study, but with even less structure.⁴ Syllable sharing gradually decreased to a distance of 10 km, but beyond this distance sharing was stochastic at a substantial and constant level no matter how far apart the individuals were, to over 670 km. No regional patterns were evident. In fact the horizontal plateau of syllable similarity between individuals beyond 10 km apart was maintained at the same level even if songs from the New York sample were included.

House finches on Hawaii were probably introduced there from the west coast of the United States, but a comparison of songs from Oahu and California yielded no particular area of California that stood out as a likely origin point—thus, song apparently cannot be used as an indicator of ancestry, or else the Hawaiian birds originated from elsewhere. Within Oahu, house finch songs are related stochastically, with no pattern of decay of similarity by distance. When Hawaiian and Californian songs are compared, syllables from Hawaii have a higher minimum frequency, but syllables from California have higher complexity (excursion and concavity). This is consistent with predictions from urban noise: Oahu is noiser than the largely suburban areas of California where house finches were recorded; thus Hawaiian birds sing songs that are simpler and with frequencies that rise above road noise.³ 

1. Geller, Frances C. (in prep). [Cultural Evolution of Bird Song]. PhD dissertation.
2. Ferrari, Leora. (in prep). Three decades of cultural evolution in California house finch song. Master’s thesis.
3. Castillo, Wendy. (in prep). Song variation and urban noise in Hawaiian house finches. Master’s thesis.
4. Roginek, Eric W., Jacquelyn Song, & David C. Lahti (in revision). Geographic variation in house finch (Haemorhous mexicanus) song along the American southwest coast.
5. *Youngblood, Mason P. & David C. Lahti. 2022. Content bias in the cultural evolution of house finch song. Animal Behaviour 185:37-48.
6. Youngblood, Mason. 2021. From Psychology to Phylogeny: Bridging Levels of Analysis in Cultural Evolution. PhD dissertation, City University of New York, Doctoral Program in Psychology. New York, NY. 202 + xxviii pp.
7. *Kornreich, Ar, Mason Youngblood, Paul C. Mundinger, and David C. Lahti. 2020. Female song can be as long and complex as male song in wild house finches (Haemorhous mexicanus). Wilson Journal of Ornithology 132:840-849. doi.org/10.1676/19-00126.
8. *Mann, Dan C., David C. Lahti, Laura Waddick, & Paul C. Mundinger. 2020. House finches learn canary trills. Bioacoustics. DOI: 10.1080/09524622.2020.1718551.
9. ^Lahti, David C. 2019. Tracking cultural evolution in house finch song. AOS (American Ornithological Society)News. Part I: 21 February; Part II: 22 February.
10. *Ju, Chenghui, Frances C. Geller, P. C. Mundinger, and D. C. Lahti. 2019. Four decades of cultural evolution in house finch songs. Auk: Ornithological Advances 136:1-18.
11. Mann, Daniel C. Stabilizing Forces in Acoustic Cultural Evolution: Comparing Humans and Birds. PhD dissertation, City University of New York, Doctoral Program in Linguistics. New York, NY. 206 + xvi pp.
12. Roginek, Eric W. 2018, Spatial variation of house finch (Haemorhous mexicanus) song along the American southwest coast. Master’s Thesis, Department of Biology, Queens College, City University of New York. 79 pp.
13. Ju, Chenghui. 2015. Cultural Evolution in Natural Populations: A Quantitative Bioacoustical Analysis. PhD Dissertation, City University of New York, Doctoral Program in Biology, Subprogram in Ecology, Evolution and Behavior. New York, NY. 124 + x pp
14. Maniego, Charles, Frances C. Geller, Chenghui Ju, Khaleda Khan, and D. C. Lahti. 2015. Song sharing and assessment of individual identity in house finches. A white paper to accompany the house finch (Haemorhous mexicanus) recordings of Paul C. Mundinger deposited at the Macaulay Library of Natural Sounds. Cornell Laboratory of Ornithology. 15 May, 10pp.

See also:
Cultural Evolution: Theory, Review, and Prospectus
Methodological Improvements in Bioacoustics and Ornithology
Interaction of Genetics, Learning, and Function in Songbird Vocal Development

Ecology and Invasion Biology of the Small Indian Mongoose

The small Indian mongoose (Urva auropunctata), while primarily important to our lab as an model system for rapid evolution following introduction, is also more broadly important as a damaging invasive species. It has been introduced to islands all over the globe, and has been implicated in the extirpations and perhaps even extinctions of local wildlife. The species has proven very difficult to eradicate on the islands where it has become established. Contrasting with this global perspective as an introduced species, the situation in its ancestral range is very different. Public perception of the species is positive, and it enjoys legal protection from poaching (it is prized for its fur, which makes premium paintbrushes). Its biology is little known from its ancestral range, however. In addition to our evolutionary studies, then, which are described elsewhere, we have conducted a study of its habitat use and home range overlap in India,^1,3 and have constructed an extensive review of all that is currently known of the species, to relate knowledge in its ancestral and introduced ranges and to inform management and control efforts.^2,3

1. Owen, M. Aaron, A. R. Berentsen, Y. V. Jhala, & David C. Lahti (in prep). Sexual dimorphism, home range, and habitat preference of the small Indian mongoose (Urva auropunctata) in northern India.
2. Domeyko, J. A., Aaron Owen & David C. Lahti. (in prep). What we know about the small Indian mongoose (Urva auropunctata), a globally introduced mammal.
3. Owen, M. Aaron. 2017. Ecology, Evolution, and Sexual Selection in the Invasive, Globally Distributed Small Indian Mongoose (Urva auropunctata).PhD Dissertation, City University of New York, Doctoral Program in Biology, Subprogram in Ecology, Evolution and Behavior. New York, NY. 171 + xviii pp.

See also:
Rapid Evolution by Sexual Selection in the Small Indian Mongoose

Evolution, Morphology, and Function of the Hyoid Apparatus in Hawaiian Honeycreepers

The Hawaiian honeycreepers (Drepanidinae) are one of the best examples of a dramatic adaptive radiation, such that one ancestral finch diverged into a range of feeding niches and associated morphologies that rival an entire community of birds. Whereas bills, foraging behaviors, and tongues have been studied as having experienced corresponding functional divergence, the hyoid, or tongue-bone, has not received the same attention. We are finding significant variation in hyoid morphology across the group. So far we have precisely characterized this variation^1,2. The next steps are to distinguish the portion of the variation that indicates relatedness (phylogenetic signal) versus adaptation to particular foraging niches; to assess correlated variation with other features such as the cranium and tongue; and to propose functional reasons for why the hyoid varies the way it does across species.¹

1. Wasserman, Danielle (in prep). Hyoid evolution in Hawaiian honeycreepers (Fringillidae: Drepanidinae). PhD dissertation.
2. Wasserman, Danielle, Kerin M. Claeson & David C. Lahti (in revision). Hyoid variation in Hawaiian honeycreepers (Drepanidinae).

African Weaverbird Coloniality and Social Behavior

African weaverbirds, especially the village weaver (Ploceus cucullatus), have constituted an important research topic for me (DCL) since 1998, long before the formation of the Lab. Here our weaver research is partitioned into five projects. Three of these are complete: defenses against brood parasitism, rapid evolution following species introduction, and invasion biology. One has recently begun and is ongoing: weaverbird nest evolution. The remaining project is a series of studies, now coming to a close except for a major upcoming review,¹ that share a focus on weaver colonial nesting and social interaction especially in and around the colony.

Two early studies are observations of the interactions between nesting village weavers and other species. The village weaver, for instance in The Gambia, often builds its nest near other animal species (e.g., other weavers, herons, wasps, and humans), evidently for protection against predators. Also, a weaver nest can be a valuable commodity, being enclosed, and is sometimes commandeered by other animals (e.g., birds, bats, and snakes), sometimes as a predator, and sometimes simply as a squatter after a nest is abandoned.^7,9

A peculiar association between introduced village weavers and the cactus Stenocereus hystrix was observed in the aloe desert of northwest Dominican Republic.^7,8 Throughout Africa, the range of the village weaver is consistent with the areas that receive at least 35cm of rain on annual average, and throughout its range its breeding is dependent on rain. However, while S. hystrix was fruiting in the DR, village weavers were observed feasting on the fruits and breeding despite a lack of rain. Moreover, the cacti were plentiful beneath the weaver colony trees, suggesting that the weavers were dispersing the cactus seeds; indeed the weaver droppings were numerous and bright red like the fruits, painting the branches and ground beneath the weaver colonies.

Many weavers are considered colonial nesters, but this terminology is too imprecise, and the degree of aggregation of nests varies between and within species. For instance, in Ethiopia both Rüppell’s weaver (Ploceus galbula) and the lesser masked weaver (Ploceus intermedius) vary in the sociality or degree of aggregation of their nesting. Rüppell’s weaver can nest singly or in small clusters, or in association with the lesser masked weaver, which itself can nest in loose aggregations or bustling colonies. I propose a continuum of descriptions of nesting sociality, from solitary nesting through associative and gregarious nesting to full coloniality.⁶

An intensive investigation of an active village weaver breeding colony of over 100 nests in Ethiopia, facilitated by high-definition video throughout the daylight hours, provided us with four studies’ worth of data. Two of them focus on synchronous fleeing events, where a large proportion of the colony would suddenly depart, usually following an intrusion. Heterospecific birds of various sizes and levels of actual threat had a similar effect on these fleeing events, which resulted in measurable daily decreases in nest attendance by weaver females. Thus weaver antipredator behavior involves many “false alarms”, which exact a cost on females.⁵ Often a distinctive call is given by one of the members of the colony, which apparently stimulates the synchronous fleeing event. Weavers were more likely to flee when this call was louder and harsher (higher Wiener entropy).⁴ Not all weavers leave the colony during these events, however, and they return after different durations. An individual male was less likely to flee, and returned sooner, if it had more nesting females on its territory (village weavers are polygynous), and if it had nest constructions in process (males sabotage each other’s nests). Thus a male weaver makes a cost-benefit analysis in real time during a threat to the colony, weighing self-protection against the security of his territory and mates.⁴

The remaining two studies of the Ethiopian village weaver colony were a detailed ethogram and behavioral analysis for each sex. Females spent about 38% of the time inside their nests or interacting with the male during the pair-formation, egg-laying and early incubation period, and the remainder of the time away from the colony. Females were more likely to remain at their nests during a colony-wide disturbance if her male did not flee.³ Males spent most of their time on behaviors involved in acquiring and retaining mates, and invested more time in female choice (i.e. nestbuilding and display) than male competition (i.e. territory defense and stealing nest material). Males exhibited a tradeoff between competing with other males and attending to or building nests. When males stole nesting material, it was not to build their own nest but merely to sabotage their rivals. Tradeoffs were also evident between interacting with females and both constructing nests and leaving the colony to forage. Variation between males in their behavioral sequences were evident, but continuous.²

1. ^David C. Lahti & Bobby Habig (in prep). Social breeding and its challenges: a case study in the village weaverbird.
2. *Khan, Khaleda, Bobby Habig, & David C. Lahti. 2019. Behavioural analysis of village weavers Ploceus cucullatus in an Ethiopian breeding colony during early incubation: 2. Males. Ostrich: Journal of African Ornithology 90:233-239.
3. *Habig, Bobby, Khaleda Khan, & David C. Lahti. 2019. Behavioural analysis of village weavers Ploceus cucullatus in an Ethiopian breeding colony during early incubation: 1. Females. Ostrich: Journal of African Ornithology 90:223-231.
4. *Habig, Bobby, Patrick I. Chiyo, and David C. Lahti. 2017. Male risk-taking is related to number of mates in a polygynous bird. Behavioral Ecology 28:541-548.
5. *Habig, Bobbyand David C. Lahti. 2015. Heterospecific intrusions, synchronous fleeing, and nest attendance in a weaverbird colony. Journal of Ornithology 156:551-555.
6. *Lahti, David C. 2013. The sociality of nesting in Rüppell’s Weaver (Ploceus galbula) and the Lesser Masked Weaver ( intermedius) in an Ethiopian acacia woodland. Ostrich: Journal of African Ornithology 84:235-238.
7. Lahti, David C. 2003. Ecology and Evolution of Breeding Adaptations in the Village Weaverbird Ploceus cucullatus. Ph. D Dissertation, Ecology and Evolutionary Biology, University of Michigan. 211+xiii pp.
8. *Lahti, David C. 2003. Cactus fruits may facilitate village weaverbird (Ploceus cucullatus) breeding in atypical habitat on Hispaniola. Wilson Bulletin 115:487-489.
9. *Lahti, David C., April R. Lahti, & Mansa Dampha. 2002. Associations between nesting village weavers Ploceus cucullatus and other animal species in The Gambia. Ostrich73:59-60.

See also:
Weaverbird Nest Evolution
Invasion Biology of the Village Weaverbird
Defenses Against Brood Parasitism in Weaverbirds
Rapid Evolution in the Village Weaverbird

Parental provisioning of water to nestlings in the pied crow

Altricial birds do not generally provision water to nestlings before they fledge and leave the nest, but we documented pied crow (Corvus albus) parents filling their bills with water and pouring it into the gapes of their nestlings in The Gambia. We provided video evidence, inferred its likely function (washing sticky anthropogenic food out of the parents’ mouths and facilitating offspring swallowing), and described the parents’ unusual method of gathering and transporting the water. We also provided a short history of the relationship between bird parenting and water provisioning in general, as this hadn’t been treated summarily to date.

• David C. Lahti and Clive R. Barlow. (in review). First observations of wild altricial nestling drinking: pied crow (Corvus albus) parents concoct a rice and water soup in The Gambia

Personality and Cognition in the Domestic Rabbit

Researchers in recent decades have been inferring both personality and cognition from the ways animals behave, and have found significant differences in these traits between individuals of the same species. We might expect variation in personality and cognition to be correlated, since they’re both being produced by the same brain in any given individual. We investigated this in domestic rabbits (Oryctolagus cuniculus) by measuring behavioral traits indicative of personality (response to novel objects, and time spent exploring an area), and relating this to the same rabbits’ cognitive performance in problem-solving tasks. We found firstly that although variation in response to novel objects was somewhat repeatable within an individual, exploration time was not– the same rabbit might explore much more one day than another. Secondly, where the individuals were on the personality continuum did not relate to their cognitive ability: a good problem-solver could be shy or bold when it comes to new objects or areas.^1,2 

1. GomezdelaTorre Clavel, Macarena G., Mason Youngblood, & David C. Lahti. (in revision). Cognition does not vary with personality in domestic rabbits (Oryctolagus cuniculus). 
2. GomezdelaTorre Clavel, Macarena G. 2020. Relationship between personality and cognitive traits in domestic rabbits (Oryctolagus cuniculus). Master’s Thesis, Department of Biology, Queens College, City University of New York. 32 pp.

Bird Egg Color: Evolution and Function

Bird eggs, and in particular the appearance of eggshells in terms of ground color and markings, serve as a valuable and convenient model system for trait evolution by natural selection. The shells can preserved, the ingredients of their variation are rather simple but their effects are striking and easily measured, they are subject to a manageable set of selective agents, and they have limited plasticity such that most differences have a genetic basis.  

Our explorations of the function and evolution of bird egg appearance began with my dissertation research on why village weaver (Ploceus cucullatus) eggs are highly variable in appearance (color and spotting) between individuals and, as it turned out, extraordinarily consistent with an individual. These studies are covered in two project entries of their own, but the punch line is that, faced with a cuckoo brood parasite with egg mimicry, four traits became adaptive in the village weaver, and to a lesser extent in Rüppell’s weaver (P. galbula): (1) egg appearance variation between individuals, (2) egg appearance similarity within an individual, (3) increased complexity of egg appearance features, including spotting, all of which improve the effectiveness of (4) own egg recognition and rejection of foreign eggs.⁹

The variation in weaverbird eggs includes a lot of blue and blue-green. Many birds lay blue-green eggs, including our familiar American robin, and most other thrushes and mimids. So why do hundreds of bird species lay conspicuous blue eggs? I happened to run across a John Endler paper that demonstrated ambient light in open woodlands was a robin’s-egg blue. Is this a coincidence? Then I considered the fact that crows’ eggs are very light blue and nest high in the canopy, while catbird eggs are dark blue-green and nest low—even lower than robins on average. These facts convinced me that a solar radiation hypothesis should be tested. Then I figured that ultraviolet (UV) light can damage bird embryos, and their eyes specifically as those are the only organs that cannot develop in the egg without pigment. So I called my hypothesis “pigment as parasol”. But the situation is more complex than this, surely, as we rarely see dark eggs in nature (see below), almost certainly because they would heat up in sunlight and kill the embryo. I call this the “dark car effect”, as I experienced often in my youth while my mom was shopping. But back to eggshells, why blue-green in particular? I learned during the course of my weaverbird research that only two pigments are responsible for all known bird egg color—a reddish-brown protoporphyrin, and a blue-green biliverdin. And biliverdin has two reflectance peaks—one in the human-visible blue-green, and one in the UV. Biliverdin reflects more UV than protoporphyrin does, and any light that is reflected can’t enter the egg. Perhaps the reason why catbird eggs are dark blue-green is because they are not in much danger of heating up but still would benefit from UV protection! And the higher-nesting crow eggs would likely heat up in sunlight, so they are striking a compromise between pigment as parasol and the dark car effect. And robins are somewhere in between.⁹

I immediately (in 2003) submitted my hypothesis to the American Naturalist, one of my then favorite scientific journals; they responded that I needed more than a plausibility argument and weak circumstantial evidence. So I decided on three projects for the future: (1) look at how weaverbird eggs evolve when their ancestors had variable eggs but they have been introduced to a habitat without egg-mimicking brood parasites; (2) do a biophysics study to determine whether light transmittance through and absorbance by eggshells accords with the pigment as parasol and dark car effect hypotheses; and (3) look at genera of birds that include species with white eggs and with blue eggs (I call these “switches to blue” genera, although of course they might have included switches to white) and see if there was a change of habitat—one that would have involved a change in light exposure—associated with the change in egg color over evolutionary time.

I already knew that village weaverbird eggs lose their distinctiveness following introduction to environments without egg mimicking cuckoos. But how should bird eggs evolve when such a predominant source of natural selection is removed? That the four specific adaptations to cuckoo brood parasitism listed above should decay is a clear prediction, and this occurred. But on what color should the weaver eggs “settle” evolutionarily when there are no cuckoos around? Given that the light in an enclosed weaverbird nest is similar to an open woodland, and that a couple of African weaverbirds that are apparently unparasitized by cuckoos lay eggs of a medium blue-green similar to that of the robin, the pigment as parasol hypothesis appeared to yield the best prediction. In line with this hypothesis, weaverbirds introduced over two centuries ago from West Africa to Hispaniola, where there are no egg-mimicking brood parasites, evolved a darker (more blue-green) egg than their ancestral population has.⁸

We then conducted the biophysics study and found that the patterns that follow light impinging on eggs, in terms of reflectance, absorbance, and transmittance, are precisely what we would predict from the pigment as parasol hypothesis; and that eggs heat up the darker they are just as predicted by the dark car effect. There does appear to be a tradeoff between two ways of injuring embryos (although we haven’t tested for embryonic harm directly), and bird egg colors in various light environments appear to be governed by that tradeoff. The paper came out finally in the American Naturalist after a probably unprecedented interval of 15 years after first submission!⁴

Our lab has not yet studied any of those “switches to blue” genera to see whether predicted correlations exist between egg light environment at the nest and species-specific egg colors. We have, however, maintained a thread of general interest in bird eggs and especially the functions and evolution of egg appearance. We produced a couple of general articles, one for an encyclopedia⁷ and another as a book review³, performed one survey of egg color in all extant ratites plus the extinct elephant bird (Aepyornis)⁶ thanks to specimens in the wonderful Western Foundation of Vertebrate Zoology, and completed two more intensive studies:

Rüppell’s weaver (Ploceus galbula) is a locally common East African endemic species that is subject to brood parasitism by the diederik cuckoo (Chrysococcyx caprius). Their egg appearance as a defense against brood parasitism is dealt with in a separate section, as is a test of the relative utility of different methods of measuring and quantifying egg color. But of separate interest is the patterns of variation we saw in egg appearance. Most aspects of color and spotting are decoupled from each other, and thus can evolve independently, especially colors that derive from different pigments. In fact, although the eggs seem to exhibit continuous variation in ground color, it is actually bimodal, with one broad continuous class of off-white/ultraviolet eggs and another broad class of blue-green eggs. Variation in all other color and spotting traits is unimodal and usually normal in distribution. Interesting to note is that two of this species’ eggs can look identical to our eyes but one might have a distinct ultraviolet peak—thus some of weaverbird egg variation is cryptic or invisible to us.²

After performing that study in Ethiopia, we took the Rüppell’s weaver eggs into the lab to test whether sunlight changes their color, whether during the course of a typical incubation period or with exposure to light for instance in a natural history museum. We found that yes indeed they do change color in light, especially sunlight—the shells become duller (less chromatic) and darker (less bright).⁵

Given the solar radiation hypothesis, dark eggs in direct sunlight should be maladaptive; even if they are not in direct sunlight, dark eggs are highly unusual, result from an extensive deposition of pigment, and beg an explanation. Recently we have embarked on a study of dark eggs.¹ What species lay them? What is their ecological environment? Where did they come from phylogenetically? And, especially, why are they dark?

1. Zimmerman, Shari. (in prep). The evolution and functions of dark bird eggs. Master’s thesis.
2. ^*Lahti, David C. 2021. Analysis of egg variation and foreign egg rejection in Rüppell’s weaver (Ploceus galbula). Frontiers in Ecology & Evolution9:734126 (23 pp). DOI: 10.3389/fevo.2021.734126.
3. Ju, Chenghui and D. C. Lahti. 2017. Review of Tim Burkhead, The Most Perfect Thing: Inside (and Outside) a Bird’s Egg. Auk: Ornithological Advances 134:922-924.
4. *Lahti, David C. & Daniel R. Ardia. 2016. Shedding light on bird egg color: pigment as parasol and the dark car effect. American Naturalist187:547-563.
5. *Navarro, Johanna Y.and David C. Lahti. 2014. Light dulls and darkens bird eggs.  PLoS One 9:e116112. doi:10.1371/journal.pone.0116112.
6. Navarro, Johanna Y. Studies of environmental and evolutionary changes in bird egg color. Master’s Thesis, Department of Biology, Queens College, City University of New York. 79 + iv pp, 6 plates.
7. ^Lahti, David C. 2013. Egg. World Book Encyclopedia. Chicago: World Book.
8. *Lahti, David C. 2008. Population differentiation and rapid evolution of egg color in accordance with solar radiation. Auk 126:796-802.
9. Lahti, David C. 2003. Ecology and Evolution of Breeding Adaptations in the Village Weaverbird Ploceus cucullatus. Ph. D Dissertation, Ecology and Evolutionary Biology, University of Michigan. 211+xiii pp.

See also:
Rapid Evolution in the Village Weaverbird
Defenses Against Brood Parasitism in Weaverbirds
Methodological Improvements in Bioacoustics and Ornithology

Nestling Begging by Brood Parasitic Cuckoos

Brood parasites are reared by parents of another species; as nestlings, how do they get their parents’ attention? Do their nestling begging calls sound like those of other cuckoos because of evolutionary relatedness, or do they mimic the nestlings of their hosts (despite never having heard them, as they kick host eggs out of the nest)? We are just now embarking on an attempt to answer this question, in two African cuckoos: the diederik cuckoo (Chrysococcyx caprius) that parasitizes weaverbirds, and Klaas’s cuckoo (Chrysococcyx klaas) that parasitizes sunbirds.

• Lopez, Andrea. (in prep). Nestling begging and brood parasitism by African Chrysococcyx Master’s thesis.

African Botany and Ethnobotany

Our lab being in the northeastern United States, we have an embarrassment of riches when it comes to useful, accessible, and accurate guides to nearly any type of organism one is interested to get to know in the region. Subsaharan Africa is another story; birds and mammals are the only organisms that enjoy coverage across the region as a whole, and those field guides are well used by local people, ecotourists, and field scientists. Good field guides to other organisms have been written for only a few countries, such as South Africa, Kenya, and Tanzania. Plants experience low demand and so the resources available—whether to scientists or the nonspecialist public, are sparse. Our current ventures in this area are two.

One is an ethnobotany study, which is currently on the back burner despite being two-thirds finished: a survey of the local uses of plants for food, medicine, crafts, and magic in the island community of Janjangbureh, The Gambia, based on first-hand reports by a local expert. We also research the current state of scientific medical knowledge of each plant to which traditional Gambian lore attributes healing properties, and have discovered at least two plants whose medical uses have not yet been tested.

On the other side of the continent, Ethiopia is eager to welcome ecotourists and scientists along the lines of its southerly neighbors Kenya and Tanzania. Its Awash Valley, for instance, is famous for ancestral hominin fossil finds, and the associated Awash National Park is a beautiful area with an abundance of wildlife, a spectacular waterfall, and comfortable housing at Awash Falls Lodge. No field guide to its flowering plants exists, however, though many of the blooms are exquisite and conspicuous on the landscape. We are identifying, photographing, and describing dozens of flowers of both herbaceous and woody plants in the Awash National Park, and arranging them into a guide, to be made available in both hardcopy and online form for Ethiopians and visitors alike.

• Vazquez, Lizbeth. (in prep). Common flowering plants of the Awash National Park, Ethiopia. Master’s thesis.

Ecology of Mimicry in Northern Mockingbirds

The Northern Mockingbird (Mimus polyglottos) is one of a few birds that construct their songs not only by imitating members of their own species, but by copying any melodic sounds around them, whether produced by other birds, frogs, insects, or even human devices like sirens and car alarms. This raises the possibility that the vocal repertoire of a mockingbird can indicate where it grew up. We are comparing the songs of mockingbirds in New York and Texas to this hypothesis.

• Milander, Jacqueline (in prep). Ecology of mimicry in northern mockingbirds. Master’s thesis.

Weaverbird Nest Evolution

The evolution of behavior is difficult to study because it is transient, and often hard to quantify even when seen. Macroevolutionary history exacerbates the problem because the timescales extend further into the past and we have much less complete access to the story. Extended phenotypes are one way to mitigate this problem: if an organism’s behavior changes the environment in some way, that change in the environment can be studied like a morphological trait. Bird nests are a good example of this. They don’t survive through evolutionary history like bones do, but they can be collected and measured and compared across species using the same or similar techniques as comparative morphologists do. This opens a window into the evolution of nest-building and reproductive behavior and the factors that influence it.

We are now knee-deep in a collaborative study of the macroevolution of nest structure and function in the weaverbirds (Ploceidae), a family of especially virtuosic nestbuilders in Africa and Asia. We are attempting to reconstruct the evolution of nest design and reproductive behavior in this group, and to test evolutionary predictions about function. Would a monogamous bird tend to build a different sort of nest than a polygynous bird? How do males and females differ in their contributions? What ecological factors influence the design of a nest? To address these questions in the weaverbirds we are using molecular phylogenies and ancestral state reconstructions to map the evolution of nest design and reproductive behavior on the Ploceid tree.

• Habig, Bobby, Jackie L. Childers, & David C. Lahti (in prep). The evolution of nest-building behavior in Ploceidae weaverbirds.

See also:
Defenses Against Brood Parasitism in Weaverbirds
Bird Egg Color: Evolution and Function
African Weaverbird Coloniality and Social Behavior

 

COMPLETED (so far) PROJECTS

Is any exploration ever complete? This depends on how narrowly focused the questions are. The topics here are broad enough that in no case below is the inquiry complete. But we are limited in our bandwidth to address them at any given point. Thankfully, each of these have seen questions answered and avenues explored to positive effect. So these projects are complete… so far.  In future any of them could be expanded and bumped up to “Active Current”. And, of course, any of those current projects above—all of them, we hope!—will eventually find their way into this comfortable resting place of the Completed Projects, making way for new ones.

A temporal list forms a table of contents first, and the project descriptions and outputs follow. The outputs are mostly there, but the descriptions are a work in progress.

 

Last active 2020s:

• Interaction of Genetics, Learning, and Function in Songbird Vocal Development
• Rapid Evolution by Sexual Selection of the Small Indian Mongoose
• Cultural Evolution of Human Language, Music, and Ideas
• Teaching, Science Education and Outreach
• Defenses Against Brood Parasitism in Weaverbirds
• Methodological Improvements in Bioacoustics and Ornithology
  
• Invited Reviews on Ornithological Topics
• Professional Obituaries and Tributes
  
  

Last active 2010s:

• Conceptual and Theoretical Issues in Evolution and Animal Behavior
• Morality and Other Complex Human Traits at the Interface of Function, Evolution, and Philosophy
• Relaxed Selection and Trait Loss
  
  

Last active 2000s:

• Rapid Evolution in the Village Weaverbird
• Invasion Biology of the Village Weaverbird
• Phylogenetic Placement of the Cuckoo-Finch
• Bird Nest Predation
  
  

Last active 1990s:

• Metaethics
• Early Anthropological Literature on Native Americans

 

Interaction of Genetics, Learning, and Function in Songbird Vocal Development

The “nature-nurture” dichotomy remains a debate even with respect to animal behavior because of the difficulty of testing the relative contributions of inherited (innate) and learned (acquired) factors in behavior. Hand-rearing birds in a laboratory and controlling their sound input enable such tests for learned birdsong. We have performed studies on three bird species and yielded results that overall demonstrate a close interaction between inheritance and learning in vocal development, as well as discrete contributions of one or the other to particular traits. In swamp sparrows (Melospiza georgiana), where speed of singing and high frequency bandwidth are at a premium for acquiring mates, young males copy their tutors accurately unless they can sing better, in which case they deviate from imitation to improve upon the model. In canaries (Serinus canaria), hundreds of years of selective breeding for low-pitched songs in certain breeds has resulted in an inability to learn wild-type high pitched songs, whereas wild-type canaries have a strong inherited preference for high pitches. Finally, the house finch (Haemorhous mexicanus) has a loose learning program that facilitates great complexity and variation in its song. However, this permissiveness also allows the house finch to learn syllables sung by other species, such as the canary, especially when cross-fostered with canaries. Nevertheless, certain aspects of house finch song, such as the presence of particular sounds, remain fixed even if the young bird never hears a house finch song during development.

[include swamp sparrows have rhythm]

1. *Kornreich, Ar, Mason Youngblood, Paul C. Mundinger, and David C. Lahti. 2020. Female song can be as long and complex as male song in wild house finches (Haemorhous mexicanus). Wilson Journal of Ornithology 132:840-849. doi.org/10.1676/19-00126.
2. *Mann, Dan C., David C. Lahti, Laura Waddick, & Paul C. Mundinger. 2020. House finches learn canary trills. Bioacoustics. DOI: 10.1080/09524622.2020.1718551.
3. Mann, Daniel C. Stabilizing Forces in Acoustic Cultural Evolution: Comparing Humans and Birds. PhD dissertation, City University of New York, Doctoral Program in Linguistics. New York, NY. 206 + xvi pp.
4. *Mundinger, Paul C. & David C. Lahti. 2014. The quantitative integration of genetic factors in the learning and production of canary song. Proceedings of the Royal Society of London B281:20132631.
5. *Moseley, Dana L., David C. Lahti, and Jeff Podos. 2013. Responses to song playback vary with vocal performance of both signal senders and receivers. Proceedings of the Royal Society of London B280:2013401.
6. *Lahti, David C., Dana L. Moseley, & Jeff Podos. 2011. A performance-accuracy tradeoff in bird song learning. Ethology117:1-10.
7. ^*Podos, Jeff, David C. Lahti, & Dana L. Moseley. 2009. Performance limits and birdsong evolution. Advances in the Study of Behavior 40:159-195.
8. ^Lahti, David C. 2007. Birdsong and human speech. In M. Bekoff (ed.), Encyclopedia of Human-Animal Relationships. Westport, CT: Greenwood Publishing Group.
9. ^Lahti, David C. 2007. Similarities in vocal learning between animals and humans. In B. Bekoff (ed.), Encyclopedia of Human-Animal Relationships. Westport, CT: Greenwood Publishing Group.

Rapid Evolution by Sexual Selection in the Small Indian Mongoose

We investigated the invasive small Indian mongoose (Urva auropunctata), and found predicted evolutionary changes in sexual and communicative traits (testes and scent glands) following massive population growth on tropical islands to which this species was introduced. This was the first report of rapid evolution by sexual selection in a mammal.

1. Owen, M. Aaron, A. R. Berentsen, Y. V. Jhala, & David C. Lahti (in prep). Sexual dimorphism, home range, and habitat preference of the small Indian mongoose (Urva auropunctata) in northern India.
2. Domeyko, J. A., Aaron Owen & David C. Lahti. (in prep). What we know about the small Indian mongoose (Urva auropunctata), a globally introduced mammal.
3. *Owen, M. Aaron & David C. Lahti. 2020. Rapid evolution by sexual selection in an invasive mammal. Evolution 74:740-748.
4. Owen, M. Aaron. 2017. Ecology, Evolution, and Sexual Selection in the Invasive, Globally Distributed Small Indian Mongoose (Urva auropunctata).PhD Dissertation, City University of New York, Doctoral Program in Biology, Subprogram in Ecology, Evolution and Behavior. New York, NY. 171 + xviii pp.
5. *Owen, M. Aaron and David C. Lahti. 2015. Sexual dimorphism and condition dependence in the anal pad of the small Indian mongoose (Herpestes auropunctatus).  Canadian Journal of Zoology 93:397-402.

Cultural Evolution of Human Language, Music, and Ideas

1. *Youngblood, Mason, Karim Baraghith, & Patrick E. Savage. 2021. Phylogenetic reconstruction of the cultural evolution of electronic music via dynamic community detection (1975–1999). Evolution and Human Behavior. org/10.1016/j.evolhumbehav.2021.06.002.
2. Youngblood, Mason. 2021. From Psychology to Phylogeny: Bridging Levels of Analysis in Cultural Evolution. PhD dissertation, City University of New York, Doctoral Program in Psychology. New York, NY. 202 + xxviii pp.
3. *Youngblood, Mason P. 2020. Extremist ideology as a complex contagion: the spread of far-right radicalization in the United States between 2005 and 2017. Humanities and Social Sciences Communications 7:49 (10pp.). DOI:10.1057/s41599-020-00546-3.
4. *Jon-And, Anna & Elliot Aguilar. 2019. A model of contact-induced language change: testing the role of second language speakers in the evolution of Mozambican Portuguese. PloS ONE 14(4):e0212303 (14pp.).
5. Youngblood, Mason P. A study of collaborative sampling across international networks. Red Bull Music Academy Daily, 21 June.
6. *Youngblood, Mason P. Conformity bias in the cultural transmission of music sampling traditions. Royal Society Open Science 6:191149 (8pp.).
7. Mann, Daniel C. Stabilizing Forces in Acoustic Cultural Evolution: Comparing Humans and Birds. PhD dissertation, City University of New York, Doctoral Program in Linguistics. New York, NY. 206 + xvi pp.
8. *Youngblood, Mason P. Cultural transmission modes of music sampling traditions remain stable despite delocalization in the digital age. PLoS One doi.org/10.1371/journal.pone.0211860. 12 pp.
9. Aguilar, Elliot. 2016. Models and Methods in Cultural and Social Evolution. PhD Dissertation, City University of New York, Doctoral Program in Biology, Subprogram in Ecology, Evolution and Behavior. New York, NY. 145 + xviii pp.

Teaching, Science Education and Outreach

• *Raby, Cassandra L., Jessica A. Cusick, Ines Fürtbauer, Kirsty E. Graham, Bobby Habig, Mark E. Hauber, Joah R. Madden, Amy V. H. Strauss, & Esteban Fernández-Juricic.  2022. An inclusive venue to discuss behavioural biology research: the first global Animal Behaviour Twitter Conference. Animal Behaviour 187:191-207.
• *Habig, Bobby & Preeti Gupta. 2021. Authentic STEM research, practices of science, and interest development in an informal science education program. International Journal of STEM Education 8:57. doi:10.1186/s40594-021-00314-y.
• Morales, Cristina. 2020. A review of teaching in human and nonhuman animals. Master’s Literature Review, Department of Biology, Queens College, City University of New York. 28 pp.
• *Johnson, Norman A., David C. Lahti, & Daniel T. Blumstein. 2012. Combatting the assumption of evolutionary progress: lessons from the decay and loss of traits. Evolution: Education & Outreach. DOI 10.1007/s12052-011-0381-y.

See also:
Conceptual and Theoretical Issues in Evolution and Animal Behavior

Defenses Against Brood Parasitism in Weaverbirds

1. ^*Lahti, David C. 2021. Analysis of egg variation and foreign egg rejection in Rüppell’s weaver (Ploceus galbula). Frontiers in Ecology & Evolution9:734126 (23 pp). DOI: 10.3389/fevo.2021.734126.
2. *Lahti, David C. 2006. Persistence of egg recognition in the absence of cuckoo brood parasitism: pattern and mechanism. Evolution 60:157-168.
3. *Lahti, David C. 2005. Evolution of bird eggs in the absence of cuckoo parasitism. Proceedings of the National Academy of Sciences of the U.S.A.102:18057-18062.
4. Lahti, David C. 2003. Ecology and Evolution of Breeding Adaptations in the Village Weaverbird Ploceus cucullatus. Ph. D Dissertation, Ecology and Evolutionary Biology, University of Michigan. 211+xiii pp.
5. *Lahti, David C. & April R. Lahti. 2002. How precise is egg discrimination in weaverbirds? Animal Behaviour 63:1135-1142.

Methodological Improvements in Bioacoustics and Ornithology

• *Youngblood, Mason P. 2020. A Raspberry Pi-based, RFID-equipped birdfeeder for the remote monitoring of wild bird populations, Ringing & Migration.DOI: 10.1080/03078698.2019.1759908.
• ^*Lahti, David C. 2021. Analysis of egg variation and foreign egg rejection in Rüppell’s weaver (Ploceus galbula). Frontiers in Ecology & Evolution9:734126 (23 pp). DOI: 10.3389/fevo.2021.734126.
• *Kershenbaum, Arik, Daniel T. Blumstein, Marie A. Roch, Çaglar Akçay, Gregory Backus, Mark A. Bee, Kirsten Bohn, Yan Cao, Gerald Carter, Cristiane Cäsar, Michael Coen, Stacy L. DeRuiter, Laurance Doyle, Shimon Edelman, Ramon Ferrer-i-Cancho, Todd M. Freeberg, Ellen C. Garland, Morgan Gustison, Heidi E. Harley, Chloé Huetz, Melissa Hughes, Julia Hyland Bruno, Amiyaal Ilany, Dezhe Z. Jin, Michael Johnson, Chenghui Ju, Jeremy Karnowski, Bernard Lohr, Marta B. Manser, Brenda McCowan, Eduwardo Mercado III, Peter M. Narins, Alex Piel, Megan Rice, Roberta Salmi, Kazutoshi Sasahara, Laela Sayigh, Yu Shiu, Charles Taylor, Edgar E. Vallejo, Sara Waller, and Veronica Zamora-Guiterrez. 2014. Acoustic sequences in non-human animals: a tutorial review and prospectus. Biological Reviews  91:13-52.
• *Podos, Jeff, Dana L. Moseley, Sarah E. Goodwin, Jesse McClure, Benjamin N. Taft, Amy V. H. Strauss, Christine Rega-Brodsky, & David C. Lahti. 2016. A fine-scale, broadly applicable index of vocal performance: frequency excursion. Animal Behaviour 116:203-212.
• *^Lahti, David C. 2015. The limits of artificial stimuli in behavioral research: the umwelt gamble. Ethology 121: 529-537.

Invited Reviews of Ornithological Topics

1. ^Lahti, David C. & Bobby Habig (in prep). Social breeding and its challenges: a case study in the village weaverbird.
2. ^Lahti, David C. 2019. Tracking cultural evolution in house finch song. AOS (American Ornithological Society)News. Part I: 21 February; Part II: 22 February.
3. *^Lahti, David C. 2015. The limits of artificial stimuli in behavioral research: the umwelt gamble. Ethology121:529-537.
4. ^Lahti, David C. 2013. Egg. World Book Encyclopedia. Chicago: World Book.
5. ^Lahti, David C. & Carolyn Pytte. 2012. Sleep and bird songs. In D. Barrett & P. McNamara (eds.), Encyclopedia of Sleep and Dreams. ABC-CLIO, Santa Barbara.
6. ^Lahti, David C. 2011. Review of Handbook of the Birds of the World, vol. 15: Weavers to New World Warblers. Wilson Journal of Ornithology 123:852-853.
7. ^Lahti, David C. 2009. The place where extinction was discovered. Journal of Field Ornithology80:438-444.
8. ^Podos, Jeff & David C. Lahti. 2009. Bird radiations. In R. Gillespie & D. Clague (eds.), Encyclopedia of Islands. Berkkeley: University of California Press, pp.105-111.
9. ^*Lahti, David C. 2009. Why we have been unable to generalize about bird nest predation. Animal Conservation12:279-281.
10. ^*Podos, Jeff, David C. Lahti, & Dana L. Moseley. 2009. Performance limits and birdsong evolution. Advances in the Study of Behavior 40:159-195.
11. ^Lahti, David C. 2007. Birdsong and human speech. In M. Bekoff (ed.), Encyclopedia of Human-Animal Relationships. Westport, CT: Greenwood Publishing Group.
12. ^Lahti, David C. 2007. Similarities in vocal learning between animals and humans. In B. Bekoff (ed.), Encyclopedia of Human-Animal Relationships. Westport, CT: Greenwood Publishing Group.
13. ^Lahti, David C. 2007. Birds as symbols in human culture. In M. Bekoff (ed.), Encyclopedia of Human-Animal Relationships. Westport, CT: Greenwood Publishing Group.
14. ^Lahti, David C. 2007. Human effects on birds. In M. Bekoff (ed.), Encyclopedia of Human-Animal Relationships. Westport, CT: Greenwood Publishing Group.
15. ^Lahti, David C. 2005. The village weaverbird: marvel or menace? In R. T. Wright & B. J. Nebel, Environmental Science, 9th ed.  Englewood Cliffs, NJ: Prentice Hall, p.96.
16. ^*Lahti, David C. 2003. A case study in invasive species assessment: the village weaverbird Ploceus cucullatus. Animal Biodiversity & Conservation 26:45-54.
17. ^Lahti, David C. & April R. Lahti. 1999. The village weaver: a common bird of uncommonly great concern. Daily Observer.Banjul, The Gambia, 2 October.

Professional Obituaries and Tributes

1. ^Summers, Kyle, David C. Lahti, Stanton Braude, Beverly Strassmann, and Joan Strassmann. 2019. Obituary: The nine lives of Richard D. Alexander. Evolution & Human Behavior 40:133-139.
2. Lahti, David C. & Fernando Nottebohm. 2014. Remembering Paul Mundinger (1934-2011). Auk: Ornithological Advances 131:116-119.
3. ^Lahti, David C. 2013. Twelve (more) things about the evolution of morality that make people nauseous. In K. Summers & B. Crespi (eds.), Human Social Evolution: The Foundational Works of Richard D. Alexander. New York: Oxford University Press, pp.307-325.
4. Lahti, David C. The Works of Richard D. Alexander, A Pioneerring Evolutionary Biologist. http://richarddalexander.com (website).

Conceptual and Theoretical Issues in Evolution and Animal Behavior

1. ^Lahti, David C. 2019. Be careful with Occam’s razor, you might cut yourself. Scientific American blog: Cross Check (invited guest post). 8 May.
2. ^Lahti, David C. 2018. Evolution doesn’t eliminate, it illuminates: a comment for Dr. Shoppa of St. Francis College. ASEBL Journal 18:7-10.
3. ^Lahti, David C. 2018. Behavior. Inference: International Review of Science 3(4).
4. ^Lahti, David C. 2016. An ambivalent amphibian. Inference: International Review of Science 2(4).
5. ^Lahti, David C. 2016. Converging all the way to the (tangled) bank. (A review of Simon Conway Morris’ Runes of Evolution: How the Universe Became Self-Aware). Science and Christian Belief28:125-127.
6. *^Lahti, David C. 2015. The limits of artificial stimuli in behavioral research: the umwelt gamble. Ethology121:529-537.
7. ^Lahti, David C. 2014. On explanation in evolutionary biology. In W. Thorson (ed.), The Woodpecker’s Purpose: A Scientific and Theological Critique of Intelligent Design. Wenham, MA: Gordon College CFI, pp.135-142.
8. ^Lahti, David C. 2013. Loving evolution from a distance (a review of Conor Cunningham’s Darwin’s Pious Idea). Science and Christian Belief25:170-171.
9. *Johnson, Norman A., David C. Lahti, & Daniel T. Blumstein. 2012. Combatting the assumption of evolutionary progress: lessons from the decay and loss of traits. Evolution: Education & Outreach. DOI 10.1007/s12052-011-0381-y.

See also:
Cultural Evolution: Theory, Review, and Prospectus
Teaching, Science Education and Outreach
Morality and Other Complex Human Traits at the Interface of Function, Evolution, and Philosophy

Morality and Other Complex Human Traits at the Interface of Function, Evolution, and Philosophy

1. Lahti, David C. (in prep). A conception of the ideal as the linchpin of morality.
2. Goodman, Jonathan R. 2018. Does everything flow? A Reply to Sparks. Association for the Study of Evolutionary Biology in Literature Journal 18:28-30.
3. Goodman, Jonathan R. The importance of practical understanding for altruistic behavior. Association for the Study of Evolutionary Biology in Literature Journal 18:10-17. Plus a reply by Jacob Sparks.
4. ^Lahti, David C. 2014. On the partnership between natural and moral philosophy. In H. Putnam, S. Neiman, and J. Schloss (eds.), Understanding Moral Sentiments. New Brunswick, NJ: Transaction Press, pp.229-256.
5. ^Lahti, David C. 2013. Twelve (more) things about the evolution of morality that make people nauseous. In K. Summers & B. Crespi (eds.), Human Social Evolution: The Foundational Works of Richard D. Alexander. New York: Oxford University Press, pp.307-325.
6. ^*Lahti, David C. 2011. Why humans discover. Euresis Journal 1:75-89.
7. ^Lahti, David C. 2009. The correlated history of social organization, morality, and religion. In E. Voland & W. Schiefenhövel (eds.), The Evolution of Religious Mind and Behavior. New York: Springer-Verlag, pp.67-88.
8. *Lahti, David C. & Bret S. Weinstein. 2005. The better angels of our nature: group stability and the evolution of moral tension. Evolution & Human Behavior26:47-63.
9. ^Lahti, David C. 2004. “You have heard… but I tell you…”: a test of the adaptive significance of moral evolution. In P. Clayton & J. Schloss (eds.) Evolution & Ethics. Grand Rapids, MI: Eerdmans, pp.132-150.
10. *Lahti, David C. 2003. Parting with illusions in evolutionary ethics. Biology & Philosophy18:639-651.
11. Lahti, David C. 1998. An Appraisal of Ethical Naturalism. D. Dissertation, Moral Philosophy. The Whitefield Institute Oxford. 242+viii pp.

Relaxed Selection and Trait Loss

Evolutionary theory is well-developed in the area of adaptation and natural selection; indeed, most evolutionary biologists have assumed that organismal traits become more functional and efficacious over time. However, for every trait that is gaining function, at least one (and some theorists suggest many more) is losing functionality due to changing environments or the evolution of other traits. Thus, selection can often be relaxed on certain traits because they are no longer useful or advantageous. I chaired a National Evolutionary Synthesis Center (NESCent) Working Group on Relaxed Selection and Trait Loss in Evolution between 2007-2010. Our main goal was to develop theory and propose new directions for the study of those situations where traits are losing functional integrity rather than gaining it. The fruits of this venture began in 2009 with a prominent (cover story) article in Trends in Ecology & Evolution. We followed this up with a paper promoting a more balanced perspective on trait evolution in science education. Continuing work in this area falls under two other projects in this list: “Rapid evolution following species introduction” and “Function and evolution of bird egg color”.

1. *Johnson, Norman A., David C. Lahti, & Daniel T. Blumstein. 2012. Combatting the assumption of evolutionary progress: lessons from the decay and loss of traits. Evolution: Education & Outreach. DOI 10.1007/s12052-011-0381-y.
2. *Lahti, David C., Norman A. Johnson, Beverly C. Ajie, Sarah P. Otto, Andrew P. Hendry, Daniel T. Blumstein, Richard G. Coss, Kathleen Donohue, & Susan A. Foster. 2009. Relaxed selection in the wild. Trends in Ecology & Evolution 24:487-496.
3. *Lahti, David C. 2006. Persistence of egg recognition in the absence of cuckoo brood parasitism: pattern and mechanism. Evolution 60:157-168.
4. *Lahti, David C. 2005. Evolution of bird eggs in the absence of cuckoo parasitism. Proceedings of the National Academy of Sciences of the U.S.A.102:18057-18062.
5. Lahti, David C. 2003. Ecology and Evolution of Breeding Adaptations in the Village Weaverbird Ploceus cucullatus. Ph. D Dissertation, Ecology and Evolutionary Biology, University of Michigan. 211+xiii pp.

Rapid Evolution in the Village Weaverbird

Evolution by natural selection is rarely demonstrated in the historical period in natural populations of vertebrates. Using anthropogenic species introductions as a “natural experiment”, together with predictions based on differences in selective regime between the ancestral and introduced ranges, my early research documented predicted evolutionary changes in egg appearance in the African village weaverbird (Ploceus cucullatus) following release from an egg-mimicking brood parasitic cuckoo.

• *Lahti, David C. 2008. Population differentiation and rapid evolution of egg color in accordance with solar radiation. Auk 126:796-802.
• *Lahti, David C. 2006. Persistence of egg recognition in the absence of cuckoo brood parasitism: pattern and mechanism. Evolution 60:157-168.
• *Lahti, David C. 2005. Evolution of bird eggs in the absence of cuckoo parasitism. Proceedings of the National Academy of Sciences of the U.S.A.102:18057-18062.
• Lahti, David C. 2003. Ecology and Evolution of Breeding Adaptations in the Village Weaverbird Ploceus cucullatus. Ph. D Dissertation, Ecology and Evolutionary Biology, University of Michigan. 211+xiii pp.

Invasion Biology of the Village Weaverbird

1. ^Lahti, David C. 2005. The village weaverbird: marvel or menace? In R. T. Wright & B. J. Nebel, Environmental Science, 9th ed.  Englewood Cliffs, NJ: Prentice Hall, p.96.
2. Lahti, David C. 2003. Ecology and Evolution of Breeding Adaptations in the Village Weaverbird Ploceus cucullatus. Ph. D Dissertation, Ecology and Evolutionary Biology, University of Michigan. 211+xiii pp.
3. ^*Lahti, David C. 2003. A case study in invasive species assessment: the village weaverbird Ploceus cucullatus. Animal Biodiversity & Conservation 26:45-54.
4. ^Lahti, David C. & April R. Lahti. 1999. The village weaver: a common bird of uncommonly great concern. Daily Observer.Banjul, The Gambia, 2 October.

Phylogenetic Placement of the Cuckoo-Finch

• *Lahti, David C. & Robert B. Payne. 2003. Morphological and behavioural evidence of relationships of the cuckoo-finch Anomalospiza imberbis. Bulletin of the British Ornithologists’ Club 123:113-124.

Bird Nest Predation

1. ^*Lahti, David C. 2009. Why we have been unable to generalize about bird nest predation. Animal Conservation12:279-281.
2. *Lahti, David C. 2001. The ‘edge effect on nest predation’ hypothesis after 20 years. Biological Conservation 99:365-374.

Metaethics

1. ^Lahti, David C.  2014.  On the partnership between natural and moral philosophy. In H. Putnam, S. Neiman, and J. Schloss (eds.), Understanding Moral Sentiments.  New Brunswick, NJ: Transaction Press, pp. 229-256.
2. ^Lahti, David C.  2013.  Twelve (more) things about the evolution of morality that make people nauseous. In K. Summers and B. Crespi (eds.), Human Social Evolution: The Foundational Works of Richard D. Alexander. New York: Oxford University Press, pp. 307-325.
3. *Lahti, David C.  2003.  Parting with illusions in evolutionary ethics.  Biology and Philosophy 18: 639-651.
4. Lahti, David C.  1998.  An Appraisal of Ethical Naturalism. Ph.D. Dissertation, Moral Philosophy, Whitefield Institute Oxford. 242+viii pp.

Early Writings Regarding Native American Peoples

• Lahti, David C. 1995. The Edward Payson Vining Collection: A Guide to Literature Dealing with the American Indian. Wenham, MA: Gordon College. 424+xxxiii pp.

Topical List

Failed, stalled, ill-fated, dead-end, forlorn, and forgotten projects

Lest anyone think that research projects are all successes, or even all completed eventually, here is a sobering list of the projects we once thought were promising, which, sad to say, more than double the number of completed and current projects combined. All of these I or we initially dove into with gusto, but for various reasons (departure of researchers, scoops by other labs, inadequate methods, poor data, practical difficulties, insufficient time, loss of interest, lack of funding, or distraction by new projects) never saw success.

White-backed night heron courtship	The genetic basis of trait loss (review)	Conceptual clarity in cultural evolution
Human impacts on evolution of Darwin’s finches	The functions of bird egg color (review)	Interaction between color and song in the domestic canary
The effect of forest fragmentation on bird nest predation	Unanswered questions in cultural evolution (edited paper)	Weaverbird egg color in relation to nest light environment
Success of guiding humans to honey by Indicator honeyguides in South Africa, Zambia, and Ghana	Function and evolution of egg color in Mimus/ Nesomimus/Mimodes mockingbirds	Macroevolution of weaverbird egg color variation and defenses against brood parasitism
Identification and tactics of nest predators of the veery	Parallels in virtuosity of bird and human singers	Foot functional morphology in cuckoos and plantain-eaters
The influence of roads and firebreaks on bird nest predation	Function and evolution of egg color in the Thryothorus wren complex	Relationship between cap color and song performance in swamp sparrows
Influence of nest site, plant, and habitat on indigo bunting reproductive success	The Evolution of Behavior textbook (new edition of Jerram Brown)	Meta-analysis of the heritability of behavioral versus morphological traits
Function and evolution of egg color in Tarsiger bush-robins	Rapid evolution following species introduction (review)	Function and evolution of egg color in Oenanthe wheatears
Function and evolution of egg color in Monticola rock-thrushes	Genetic and social inheritance of song features in wild swamp sparrows	Quality control in studies of ultraviolet communication signals
Function and evolution of egg color in Garrulax laughing-thrushes	Changes in genetic diversity following introductions of the village weaverbird	Population dynamics of the village weaverbird in West Africa
Evolution of egg color in ratites and tinamous	Macroevolution of Ploceus weaverbird song	Dispersal and migration of New York house finches
An integrated theory of the functional evolution of bird egg color	Multiple independent origins of cardinal mimicry in house finches	The impact of eggshell color on ultraviolet damage to bird embryos
Integration of synchronic and allochronic cultural evolutionary studies of song in the house finch	Phylogenetic, coalescent, and cultural evolutionary analysis of house finch song across populations	Genetic and cultural divergence of ancestral and introduced populations of the house finch
The importance of ultraviolet reflectance and transmission in behavioral ecology	Methodological issues and opportunities in studies of human sexual selection	Bimodality of bill and head morphology in the medium ground finch
Plastic traits under relaxed selection	Bird songs in human culture	Applications of relaxed selection
Vocal ontogeny suggests relation between inherited and learned factors in swamp sparrow song	Experimental test of the influence of eggshell color on hatchability in various light environments	Changes in eggshell opacity and color over embryonic development in the village weaverbird
Movement of small mammals in fragmented landscapes	Patterns of nest predation in African birds (review)	Contributions of scales and skin to piranha coloration
Scent marking and sexual selection in the small Indian mongoose	Issues and opportunities in the use of the comparative method to study adaptation	Patterns of egg recognition and rejection in hosts of brood parasites (review)
Defenses against brood parasitism in the lesser masked weaver	Ultraviolet damage to vertebrate embryos (review)	Estimating generation time in birds
Advancing bioacoustics analysis for the study of temporal change and spatial variation	Ecological and historical correlates of moral diversity among West African peoples	Attempted versus successful brood parasitism of weavers by diederik cuckoos
Relaxed selection and trait loss in evolution (review)	Influences on song model choice in swamp sparrows	Qualitative and quantitative lexicons of New York house finch song
The role of relaxed natural selection in animal domestication	Ontogeny of egg discrimination in the village weaverbird	Mating display synchrony in colonies of the village weaverbird