Editing Bird vocalization (section)

==Learning==
[[File:Bird song development timeline.svg|thumb|400px|A timeline for song learning in different species. Diagram adapted from Brainard & Doupe, 2002.<ref name="Brainard 2002 351-358">{{cite journal |author1=Brainard, M. S. |author2=Doupe, A. J. |name-list-style=amp|year=2002 |title=What songbirds teach us about learning |journal=Nature |volume=417 |pages=351–358 |doi=10.1038/417351a |pmid=12015616 |bibcode=2002Natur.417..351B |issue=6886|s2cid=4329603 }}</ref>]]
[[File:Superb lyrebird mimicking Australian native birds.ogg|left|thumb|[[Superb lyrebird]] mimicking several different native Australian bird calls]]
[[File:Toxostoma rufum - Brown Thrasher XC136055.ogg|left|thumb|Sample of the rich repertoire of the [[brown thrasher]]]]
The songs of different species of birds vary and are generally typical of the species. Species vary greatly in the complexity of their songs and in the number of distinct kinds of song they sing (up to 3000 in the [[brown thrasher]]); individuals within some species vary in the same way. In a few species, such as [[lyrebird]]s and [[mockingbird]]s, songs imbed arbitrary elements learned in the individual's lifetime, a form of mimicry (though maybe better called "appropriation" (Ehrlich et al.), as the bird does not pass for another species). As early as 1773, it was established that birds learned calls, and [[cross-fostering]] experiments succeeded in making linnet ''[[Acanthis cannabina]]'' learn the song of a skylark, ''[[Eurasian skylark|Alauda arvensis]]''.<ref>{{cite journal |author=Barrington, D. |year=1773 |title=Experiments and observations on the singing of birds |journal=Philosophical Transactions of the Royal Society |volume=63 |pages=249–291 |doi=10.1098/rstl.1773.0031|s2cid=186207885 }}</ref> In many species, it appears that although the basic song is the same for all members of the species, young birds learn some details of their songs from their fathers, and these variations build up over generations to form [[dialects]].<ref>{{cite journal |author=Marler, P. |author2=M. Tamura |year=1962 |title=Song dialects in three populations of the white-crowned sparrow|journal= Condor |volume=64 |issue=5 |pages=368–377 |doi=10.2307/1365545 |jstor=1365545}}</ref>

Song learning in juvenile birds occurs in two stages: sensory learning, which involves the juvenile listening to the father or other conspecific bird and memorizing the spectral and temporal qualities of the song (song template), and sensorimotor learning, which involves the juvenile bird producing its own vocalizations and practicing its song until it accurately matches the memorized song template.<ref>{{cite journal|author=Konishi, M.|year=2010|title=From central pattern generator to sensory template in the evolution of birdsong|journal=Brain & Language|volume=115|issue=1|pages=18–20|pmid= 20955898|doi=10.1016/j.bandl.2010.05.001|s2cid=205791930}}</ref>

During the sensorimotor learning phase, song production begins with highly variable sub-vocalizations called "sub-song", which is akin to [[babbling]] in human infants. Soon after, the juvenile song shows certain recognizable characteristics of the imitated adult song, but still lacks the stereotypy of the crystallized song – this is called "plastic song".<ref name = "Nottebohm 2005" >{{cite journal |author=Nottebohm, F. |year=2005 |title=The Neural Basis of Birdsong|journal=PLOS Biol|pmid=15884976|volume=3 |issue=5 |pmc=1110917|page=163 |doi=10.1371/journal.pbio.0030164 |doi-access=free }}</ref>

After two or three months of song learning and rehearsal (depending on species), the juvenile produces a crystallized song, characterized by spectral and temporal stereotypy (very low variability in syllable production and syllable order).<ref name="Leonardo1999">{{cite journal|author1=Leonardo, A. |author2= Konishi, M. |year=1999|title=Decrystallization of adult birdsong by perturbation of auditory feedback|journal=Nature |volume= 399|pages=466–470|doi=10.1038/20933 |pmid=10365958|bibcode= 1999Natur.399..466L |issue=6735|s2cid= 4403659 }}</ref> Some birds, such as [[zebra finch]]es, which are the most popular species for birdsong research, have overlapping sensory and sensorimotor learning stages.<ref name="Brainard 2002 351-358"/>

Research has indicated that birds' acquisition of song is a form of [[motor learning]] that involves regions of the [[basal ganglia]]. Further, the PDP (see ''Neuroanatomy'' below) has been considered [[Homology (biology)|homologous]] to a mammalian motor pathway originating in the [[cerebral cortex]] and descending through the [[brain stem]], while the AFP has been considered homologous to the mammalian cortical pathway through the basal ganglia and thalamus.<ref name = "Nottebohm 2005"/> Models of bird-song motor learning can be useful in developing models for how humans learn [[speech]].<ref>{{cite journal |first1=Ikuko |last1=Teramitsu |first2=Lili C. |last2=Kudo |first3=Sarah E. |last3=London |first4=Daniel H. |last4=Geschwind |first5=Stephanie A. |last5=White|name-list-style=amp|year=2004|title=Parallel FoxP1 and FoxP2 expression in songbird and human brain predicts functional interaction|journal=J. Neurosci.|volume=24|issue=13|pages=3152–63|doi=10.1523/JNEUROSCI.5589-03.2004|pmid=15056695|pmc=6730014 }}</ref>

In some species such as zebra finches, learning of song is limited to the first year; they are termed "age-limited" or "close-ended" learners. Other species such as the canaries can develop new songs even as sexually mature adults; these are termed "open-ended" learners.<ref>{{cite journal|author=Nottebohm, F.|year=2004|title= The road we travelled: discovery, choreography, and significance of brain replaceable neurons|journal= Annals of the New York Academy of Sciences|volume=1016|issue=1|pages=628–658|doi=10.1196/annals.1298.027|pmid=15313798|bibcode=2004NYASA1016..628N|s2cid=11828091}}</ref><ref>{{cite journal |last1=Brenowitz |first1=Eliot A. |first2=Michael D. |last2=Beecher |name-list-style=amp |year=2005 |title=Song learning in birds: diversity and plasticity, opportunities and challenges |journal=Trends in Neurosciences |volume=28 |issue=3 |pages=127–132 |url=http://faculty.washington.edu/beecher/B%26B-TINS.pdf |doi=10.1016/j.tins.2005.01.004 |pmid=15749165 |s2cid=14586913 |access-date=2007-10-14 |archive-date=2022-02-12 |archive-url=https://web.archive.org/web/20220212022448/http://faculty.washington.edu/beecher/B%26B-TINS.pdf |url-status=live }}</ref>

Researchers have hypothesized that learned songs allow the development of more complex songs through cultural interaction, thus allowing intraspecies dialects that help birds to identify kin and to adapt their songs to different acoustic environments.<ref>{{cite journal|doi=10.1080/08927014.1989.9525529 |author=Slater, P. J. B.|year=1989|title=Bird song learning: causes and consequences |journal= Ethol. Ecol. Evol.|volume=1|issue=1 |pages=19–46|bibcode=1989EtEcE...1...19S }}</ref>

=== Auditory feedback in birdsong learning ===
Early experiments by Thorpe in 1954 showed the importance of a bird being able to hear a tutor's song. When birds are raised in isolation, away from the influence of conspecific males, they still sing. While the song they produce, called "isolate song", resembles the song of a wild bird, it shows distinctly different characteristics from the wild song and lacks its complexity.<ref>{{cite journal|author=Thorpe, W.|year=1954|title=The process of song-learning in the chaffinch as studied by means of the sound spectrograph|journal=Nature|volume=173|issue=4402|pages=465–469|doi=10.1038/173465a0|bibcode=1954Natur.173..465T|s2cid=4177465}}</ref><ref>{{cite journal|author=Metzmacher, M.|year=2016|title=Alauda: Chaffinch song learning : Thorpe conclusions revisited|journal=Alauda|volume=84|pages=465–469|hdl=2268/204189}}</ref> The importance of the bird being able to hear itself sing in the sensorimotor period was later discovered by Konishi. Birds deafened before the song-crystallization period went on to produce songs that were distinctly different from the wild type and isolate song.<ref>{{cite journal|author=Konishi, M.|year=1965|title=The role of auditory feedback on the control of vocalization in the white-crowned sparrow|journal=Zeitschrift für Tierpsychologie|volume=22|issue=7|pages=770–783|doi=10.1111/j.1439-0310.1965.tb01688.x|pmid=5874921|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1439-0310.1965.tb01688.x|access-date=2020-02-01|archive-date=2020-02-01|archive-url=https://web.archive.org/web/20200201071527/https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1439-0310.1965.tb01688.x|url-status=live|url-access=subscription}}</ref><ref>{{cite journal|author=Marler, P.|year=1970|title=A comparative approach to vocal learning: Song development in the white-crowned sparrows|journal=Journal of Comparative and Physiological Psychology|volume=71|issue=2, Pt.2|pages=1–25|doi=10.1037/h0029144}}</ref> Since the emergence of these findings, investigators have been searching for the neural pathways that facilitate sensory/sensorimotor learning and mediating the matching of the bird's own song with the memorized song template.

Several studies in the 1990s have looked at the neural mechanisms underlying birdsong learning by performing lesions to relevant brain structures involved in the production or maintenance of song or by deafening birds before and/or after song crystallization. Another experimental approach was recording the bird's song and then playing it back while the bird is singing, causing perturbed auditory feedback (the bird hears the superposition of its own song and a fragmented portion of a previous song syllable).<ref name="Leonardo1999" /> After Nordeen & Nordeen<ref>{{cite journal|author1=Nordeen, K.W.|author2=Nordeen, E.J.|year=1994|title=Auditory feedback is necessary for the maintenance of stereotyped song in adult zebra finches|journal=Behavioral and Neural Biology|volume=71|issue=1|pages=58–66|doi=10.1016/0163-1047(92)90757-U|pmid=1567334}}</ref> made a landmark discovery as they demonstrated that auditory feedback was necessary for the maintenance of song in adult birds with crystallized song, Leonardo & Konishi (1999) designed an auditory feedback perturbation protocol in order to explore the role of auditory feedback in adult song maintenance further, to investigate how adult songs deteriorate after extended exposure to perturbed auditory feedback, and to examine the degree to which adult birds could recover crystallized song over time after being removed from perturbed feedback exposure. This study offered further support for role of auditory feedback in maintaining adult song stability and demonstrated how adult maintenance of crystallized birdsong is dynamic rather than static.

Brainard & Doupe (2000) posit a model in which LMAN (of the anterior forebrain) plays a primary role in error correction, as it detects differences between the song produced by the bird and its memorized song template and then sends an instructive error signal to structures in the vocal production pathway in order to correct or modify the motor program for song production. In their study, Brainard & Doupe (2000) showed that while deafening adult birds led to the loss of song stereotypy due to altered auditory feedback and non-adaptive modification of the motor program, lesioning LMAN in the anterior forebrain pathway of adult birds that had been deafened led to the stabilization of song (LMAN lesions in deafened birds prevented any further deterioration in syllable production and song structure).

Currently{{When|date=August 2022}}, there are two competing models that elucidate the role of LMAN in generating an instructive error signal and projecting it to the motor production pathway:

''Bird's own song (BOS)-tuned error correction model''

: During singing, the activation of LMAN neurons will depend on the match between auditory feedback from the song produced by the bird and the stored song template. If this is true, then the firing rates of LMAN neurons will be sensitive to changes in auditory feedback.

''Efference copy model of error correction''

: An [[efference copy]] of the motor command for song production is the basis of the real-time error-correction signal. During singing, activation of LMAN neurons will depend on the motor signal used to generate the song, and the learned prediction of expected auditory feedback based on that motor command. Error correction would occur more rapidly in this model.

Leonardo<ref>{{cite journal|author=Leonardo, A.|year=2004|title=Experimental test of error-correction birdsong model|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=101|issue=48|pages=16935–16940|doi=10.1073/pnas.0407870101|pmc=534752|pmid=15557558|doi-access=free}}</ref> tested these models directly by recording spike rates in single LMAN neurons of adult zebra finches during singing in conditions with normal and perturbed auditory feedback. His results did not support the BOS-tuned error correction model, as the firing rates of LMAN neurons were unaffected by changes in auditory feedback and therefore, the error signal generated by LMAN appeared unrelated to auditory feedback. Moreover, the results from this study supported the predictions of the efference copy model, in which LMAN neurons are activated during singing by the efference copy of the motor signal (and its predictions of expected auditory feedback), allowing the neurons to be more precisely time-locked to changes in auditory feedback.

==== Mirror neurons and vocal learning ====
A [[mirror neuron]] is a [[neuron]] that discharges both when an individual performs an action and when he/she perceives that same action being performed by another.<ref name="Rizzolatti, G. 2004">{{cite journal|last1=Rizzolatti |first1=Giacomo|last2=Craighero |first2=Laila |s2cid=1729870|year=2004|title=The mirror-neuron system|journal=Annu. Rev. Neurosci.|volume=27|pages=169–192|doi=10.1146/annurev.neuro.27.070203.144230|pmid=15217330}}</ref> These neurons were first discovered in [[macaque]] monkeys, but recent research suggests that mirror neuron systems may be present in other animals including humans.<ref>{{cite journal|author1=Oberman, L. M.|author2=Pineda, J. A.|author3=Ramachandran, V. S.|year=2007|title=The human mirror neuron system: A link between action observation and social skills|journal=Social Cognitive and Affective Neuroscience|volume=2|issue=1|pages=62–66|doi=10.1093/scan/nsl022|pmc=2555434|pmid=18985120}}</ref>[[File:Song selective HVCx neurons.svg|thumb|300px|'''Song selectivity in HVCx neurons:''' neuron activity in response to calls heard (green) and calls produced (red). '''a.''' Neurons fire when the primary song type is either heard or sung. '''b, c.''' Neurons do not fire in response to the other song type, regardless of whether it is heard or sung.<ref name="Prather2008">{{cite journal|author1=Prather J. F.|author2=Peters S.|author3=Nowicki S.|author4=Mooney R.|year=2008|title=Precise auditory-vocal mirroring in neurons for learned vocal communication|journal=Nature|volume=451|issue=7176|pages=305–310|doi=10.1038/nature06492|pmid=18202651|bibcode=2008Natur.451..305P|s2cid=4344150}}</ref>]]

Mirror neurons have the following characteristics:<ref name="Rizzolatti, G. 2004"/>
* They are located in the [[premotor cortex]].
* They exhibit both sensory and motor properties.
* They are action-specific – mirror neurons are only active when an individual is performing or observing a certain type of action (e.g., grasping an object).

Because mirror neurons exhibit both [[sensory neuron|sensory]] and [[motor neuron|motor]] activity, some researchers have suggested that mirror neurons may serve to map sensory experience onto motor structures.<ref name="Dinstein, I. 2008">{{cite journal|author1=Dinstein, I.|author2=Thomas, C.|author3=Behrmann, M.|author4=Heeger, D.J.|year=2008|title=A mirror up to nature|journal=Current Biology|volume=18|issue=1|pages=R13–18|doi=10.1016/j.cub.2007.11.004|pmc=2517574|pmid=18177704|bibcode=2008CBio...18..R13D }}</ref> This has implications for birdsong learning– many birds rely on auditory feedback to acquire and maintain their songs. Mirror neurons may be mediating this comparison of what the bird hears, how it compares to a memorized song template, and what he produces.

In search of these auditory-motor neurons, Jonathan Prather and other researchers at Duke University recorded the activity of single neurons in the [[High vocal center|HVCs]] of [[swamp sparrow]]s.<ref name="Prather2008"/> They discovered that the neurons that project from the HVC to Area X (HVC<sub>X</sub> neurons) are highly responsive when the bird is hearing a playback of his own song. These neurons also fire in similar patterns when the bird is singing that same song. Swamp sparrows employ 3–5 different song types, and the neural activity differs depending on which song is heard or sung. The HVC<sub>X</sub> neurons only fire in response to the presentation (or singing) of one of the songs, the primary song type. They are also temporally selective, firing at a precise phase in the song syllable.

Prather, et al. found that during the short period of time before and after the bird sings, his HVC<sub>X</sub> neurons become insensitive to [[Sound|auditory]] input. In other words, the bird becomes "deaf" to his own song. This suggests that these neurons are producing a [[corollary discharge]], which would allow for direct comparison of motor output and auditory input.<ref>{{cite journal|author1=Tchernichovski, O.|author2=Wallman, J.|year=2008|title=Behavioral neuroscience: Neurons of imitation|journal=Nature|volume=451|issue=7176|pages=249–250|doi=10.1038/451249a|pmid=18202627|bibcode=2008Natur.451..249T|s2cid=205035217|doi-access=free}}</ref> This may be the mechanism underlying learning via auditory feedback. These findings are also in line with Leonardo's (2004) efference copy model of error correction in birdsong learning and production.

Overall, the HVC<sub>X</sub> auditory motor neurons in swamp sparrows are very similar to the visual motor mirror neurons discovered in [[primates]]. Like mirror neurons, the HVC<sub>X</sub> neurons:

* Are located in a [[premotor]] brain area
* Exhibit both sensory and motor properties
* Are action-specific – a response is only triggered by the "primary song type"

The function of the mirror neuron system is still unclear. Some scientists speculate that mirror neurons may play a role in understanding the actions of others, [[imitation]], [[theory of mind]] and [[language acquisition]], though there is currently insufficient [[neurophysiology|neurophysiological]] evidence in support of these theories.<ref name="Dinstein, I. 2008"/> Specifically regarding birds, it is possible that the mirror neuron system serves as a general mechanism underlying [[vocal learning]], but further research is needed. In addition to the implications for song learning, the mirror neuron system could also play a role in [[territorial behavior]]s such as song-type matching and countersinging.<ref>{{cite journal |author=Miller, G. |year=2008 |title=Mirror neurons may help songbirds stay in tune |journal=Science |volume=319 |issue=5861 |page=269 |doi=10.1126/science.319.5861.269a |pmid=18202262 |s2cid=34367648 }}</ref><ref>{{cite journal|url= |title=Auditory–vocal mirroring in songbirds|first=Richard |last=Mooney|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|date=5 June 2014|volume=369|issue=1644|publisher=Philosophical Transactions of the Royal Society B: Biological Sciences Online|doi=10.1098/rstb.2013.0179|pmid=24778375|pmc=4006181}}</ref>

=== Learning through cultural transmission ===
{{external media | width = 210px | float = right | headerimage= [[File:Zebra finch 1 (7325890448).jpg|210px]] | video1 = [https://www.crowdcast.io/e/bird-behavior/1 “The cultural lives of birds”], [[Knowable Magazine]], February 26, 2022 }}

[[Animal culture|Culture in animals]] is usually defined to consist of socially transmitted behavior patterns ("traditions") that are characteristic of certain populations.<ref name=":0">{{Citation|last1=Riebel|first1=Katharina|title=Chapter Six – Learning and Cultural Transmission in Chaffinch Song|date=2015-05-01|url=http://www.sciencedirect.com/science/article/pii/S0065345415000029|journal=Advances in the Study of Behavior|volume=47|pages=181–227|editor-last=Naguib|editor-first=Marc|publisher=Academic Press|language=en|doi=10.1016/bs.asb.2015.01.001|access-date=2020-01-30|last2=Lachlan|first2=Robert F.|last3=Slater|first3=Peter J. B.|editor2-last=Brockmann|editor2-first=H. Jane|editor3-last=Mitani|editor3-first=John C.|editor4-last=Simmons|editor4-first=Leigh W.|archive-date=2020-01-30|archive-url=https://web.archive.org/web/20200130042440/https://www.sciencedirect.com/science/article/pii/S0065345415000029|url-status=live|url-access=subscription}}</ref> The learned nature of bird song as well as evidence of "dialect"-like local variations have support theories about the existence of [[Animal culture#Avian culture|avian culture]].<ref name="Hyland Bruno">{{cite journal |last1=Hyland Bruno |first1=Julia |last2=Jarvis |first2=Erich D. |last3=Liberman |first3=Mark |last4=Tchernichovski |first4=Ofer |title=Birdsong Learning and Culture: Analogies with Human Spoken Language |journal=Annual Review of Linguistics |date=14 January 2021 |volume=7 |issue=1 |pages=449–472 |doi=10.1146/annurev-linguistics-090420-121034 |s2cid=228894898 |url=https://doi.org/10.1146/annurev-linguistics-090420-121034 |access-date=23 February 2022 |issn=2333-9683|url-access=subscription }}</ref><ref name="Mason"/>

As mentioned [[#Auditory feedback in birdsong learning|above]], bird song's dependence on learning was studied by Thorpe, who found that [[Common chaffinch|chaffinches]] raised in isolation from their first week of life produce highly abnormal and less complex songs compared to other chaffinches.<ref>{{Cite journal|last=Thorpe|first=W. H.|title=The Learning of Song Patterns by Birds, with Especial Reference to the Song of the Chaffinch Fringilla Coelebs|date=2008-06-28|journal=Ibis|volume=100|issue=4|pages=535–570|doi=10.1111/j.1474-919x.1958.tb07960.x|issn=0019-1019}}</ref> This suggested that many aspects of song development in songbirds depends on tutoring by older members of the same species. Later studies observed canary-like elements in the song of a chaffinch raised by [[Domestic canary|canaries]],<ref>{{Cite journal|last=Slater|first=P. J. B.|date=1983-04-01|title=Chaffinch Imitates Canary Song Elements and Aspects of Organization|journal=The Auk|volume=100|issue=2|pages=493–495|doi=10.1093/auk/100.2.493|issn=0004-8038}}</ref> evidencing the strong role of tutors in the learning of song by juvenile birds.

Similar chaffinch song types (categorized based on their distinct elements and their order) were observed to cluster in similar geographic areas,<ref>{{Cite journal|last1=Slater|first1=P. J. B.|last2=Ince|first2=S. A.|date=1979|title=Cultural Evolution in Chaffinch Song|journal=Behaviour|volume=71|issue=1/2|pages=146–166|issn=0005-7959|jstor=4534000|doi=10.1163/156853979X00142}}</ref> and this discovery led to hypotheses about "dialects" in birdsong. It has since been postulated that these song type variations are not [[dialect]]s like those we found in human language. This is because not all members of a given geographic area will conform to the same song type, and also because there is no singular characteristic of a song type that differentiates it from all other types (unlike human dialects where certain words are unique to certain dialects).<ref name=":0" />

Based on this evidence of learning and localized song types, researchers began to investigate the social learning of birdsong as a form of cultural transmission.<ref name="Mason"/><ref name="Hyland Bruno"/> The behavior patterns constituting this culture are the songs themselves, and the song types can be considered as traditions.

==== Dopamine circuits and cultural transmission ====
A recent study has shown that a dopamine circuit in zebra finches may promote social learning of bird song from tutors.<ref>{{Cite journal|last1=Tanaka|first1=Masashi|last2=Sun|first2=Fangmiao|last3=Li|first3=Yulong|last4=Mooney|first4=Richard|date=2018|title=A mesocortical dopamine circuit enables the cultural transmission of vocal behaviour|journal=Nature|language=en|volume=563|issue=7729|pages=117–120|doi=10.1038/s41586-018-0636-7|issn=1476-4687|pmc=6219627|pmid=30333629|bibcode=2018Natur.563..117T}}</ref> Their data shows that certain brain areas in juvenile zebra finches are excited by the singing of conspecific (i.e. same-species) tutors and not by loudspeakers playing zebra finch song. Additionally, they show that dopamine released into the HVC aids in the encoding of song.

=== 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.