Editing Bird vocalization (section)

=== Evolutionary preservation of bird vocal learning ===

==== The cultural trap hypothesis ====
Although a significant amount of research was done on bird song during the 20th century, none was able to elucidate the evolutionary "use" behind birdsong, especially with regards to large vocal repertoires. In response, Lachlan and Slater proposed a "cultural trap" model to explain persistence of wide varieties of song.<ref name=":1">{{Cite journal|last1=Lachlan|first1=Robert F.|last2=Slater|first2=Peter J. B.|date=1999-04-07|title=The maintenance of vocal learning by gene–culture interaction: the cultural trap hypothesis|journal=Proceedings of the Royal Society B: Biological Sciences|volume=266|issue=1420|pages=701–706|doi=10.1098/rspb.1999.0692|pmc=1689831|issn=0962-8452}}</ref> This model is based on a concept of "filters", in which:

* a male songbird's (i.e. singer's) filter contains the range of songs that it can develop
* a female songbird's (i.e. receiver's) filter contains the range of songs that it finds acceptable for [[mate choice]]

In one possible situation, the population consists mainly of birds with wide filters. In this population, a male songbird with a wide filter will rarely be chosen by the few females with narrow filters (as the male's song is unlikely to fall within a narrower filter). Such females will have a relatively small choice of males to mate with,  so the genetic basis of the females' narrow filter does not persist. Another possible situation deals with a population with mostly narrow filters. In the latter population, wide-filter males can feasibly avoid mate choice rejection by learning from older, narrow-filter males. Therefore, the average reproductive success of wide-filter birds is enhanced by the possibility of learning, and vocal learning and large song repertoires (i.e. wide filters) go hand-in-hand.<ref name=":1"/><ref name=":0"/>

The cultural trap hypothesis is one example of gene-culture coevolution, in which selective pressures emerge from the interaction between genotypes and their cultural consequences.<ref name=":1"/>

==== Possible correlation with cognitive ability ====
Various studies have shown that adult birds that underwent stress during critical developmental periods produce less complex songs and have smaller HVC brain regions.<ref>{{Cite journal|last1=Schmidt|first1=K. L.|last2=MacDougall-Shackleton|first2=E. A.|last3=Kubli|first3=S. P.|last4=MacDougall-Shackleton|first4=S. A.|date=2014-06-20|title=Developmental Stress, Condition, and Birdsong: A Case Study in Song Sparrows|journal=Integrative and Comparative Biology|volume=54|issue=4|pages=568–577|doi=10.1093/icb/icu090|pmid=24951504|issn=1540-7063|doi-access=free}}</ref><ref>{{Cite journal|first1=S.|last1=Nowicki|first2=W.|last2=Searcy|first3=S.|last3=Peters|date=2002-12-01|title=Brain development, song learning and mate choice in birds: a review and experimental test of the "nutritional stress hypothesis"|journal=Journal of Comparative Physiology A|volume=188|issue=11–12|pages=1003–1014|doi=10.1007/s00359-002-0361-3|pmid=12471497|s2cid=14298372|issn=0340-7594}}</ref> This has led some researchers to hypothesize that sexual selection for more complex songs indirectly selects for stronger cognitive ability in males.<ref>{{Cite journal|last1=Boogert|first1=N. J.|last2=Fawcett|first2=T. W.|last3=Lefebvre|first3=L.|date=2011-04-18|title=Mate choice for cognitive traits: a review of the evidence in nonhuman vertebrates|journal=Behavioral Ecology|volume=22|issue=3|pages=447–459|doi=10.1093/beheco/arq173|issn=1045-2249|doi-access=free}}</ref> Further investigation showed that male [[song sparrow]]s with larger vocal repertoires required less time to solve detour-reaching cognitive tasks.<ref>{{Cite journal|last1=Boogert|first1=Neeltje J.|last2=Anderson|first2=Rindy C.|last3=Peters|first3=Susan|last4=Searcy|first4=William A.|last5=Nowicki|first5=Stephen|date=2011|title=Song repertoire size in male song sparrows correlates with detour reaching, but not with other cognitive measures|journal=Animal Behaviour|volume=81|issue=6|pages=1209–1216|doi=10.1016/j.anbehav.2011.03.004|s2cid=21724914|issn=0003-3472}}</ref> Some have proposed that bird song (among other sexually selected traits such as flashy coloring, body symmetry, and elaborate courtship) allow female songbirds to quickly assess the cognitive skills and development of multiple males.