Editing Bird vocalization (section)

==== 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"/>