Why do Birds sing more than one song - Google Docs PDF

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Margret Forgie was the professor for this class. But we had many different people who ran the lectures....

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Why do Birds sing more than one song? ● Songbirds learn their songs, which they use to attract mates and repel rivals. The set of song types that an individual can sing is called its “repertoire”. ● Some species,like ovenbirds and white-crowned sparrows have just one song type in their repertoire. At the other extreme a brown thrasher sings over 1500 songs ● About 72% of songbird species sing more than one type of song. ● Birds produce other vocal signals known as “calls” Oscine passerine-bird having specialized vocal apparatus. Sparrow, true sparrow - any of several small dull-colored singing birds feeding on seeds or insects. lyrebird - Australian bird that resembles a pheasant; the courting male displays long tail feathers in a lyre shape Repertoires within repertoires. ● Often notes come in a group that a bird will reproduce faithfully, called a syllable. Songs-discrete strings of syllables separated from other strings by silent gaps. ● Each male sings about 27 syllable types, which he combines in different arrangements to make over 200 song types. 3 philosophical questions. ● In the past the repertoires function is the reason that natural selection caused repertoires to evolve. ● If we assume that repertoire size was a heritable trait,father with larger repertoires would have tended to have sons with larger repertoires. ● The repertoires function is the current advantage provided by singing repertoire. ● We would say repertoires currently function to attract females. ● Smaller repertoires may also have advantages ● Smaller repertoires might facilitate species recognition, require less investment in costly brain tissue or permit improved song performance. ● Song learning,territoriality, sexual behavior,male to male interactions, and parental care vary among these populations. ● The populations repertoires are made up of different numbers, structures and combinations of syllables, songs and song sequences which are delivered at different rates at different times of the day and year.

Why do songbirds sing more than one song? ● Nothing,interchangeable variety, the ability t o song match neighbours or functionally distinct signals. Repertoires have no function ● Repertoires are epiphenomena. Epiphenomena- is something that has no consequences. ● Epiphenomena hypothesis does not explain the evolution of repertoires in general. ● Bigger repertoires tend to require larger brains. ● The epiphenomena hypothesis is inadequate to explain song type repertoires is that scientist have collected a lot of evidence that repertoires do have fitness consequences. Variety for the sake of variety. ● The specific acoustic differences among song types don’t matter but the amount of variety does. Beau Geste hypothesis-proposes that song repertoires are advantageous in territory defense because non territorial males, who are prospecting for territories, use the number of song types they hear to assess the density of territorial males, and then avoid densely-settled areas. ● Birds switch song types to give the impression that there are many individuals defending the space. ● Repertoires are more effective than single songs for defending territories. ● Birds will use different locations to sing each song type to improve the illusion that there are many different birds singing. ● Studies have failed to support this hypothesis. Monotony threshold principles-is based on the idea that listeners that hear the same song repeated over and over will respond less over time a process called habituation.Monotony is supported!! Anti exhaustion hypothesis-is the mirror image of the monotony threshold principle. Whereas the monotony threshold principle states repertoires evolved to prevent the effects of monotony on listener the anti exhaustion hypothesis says that repertoires prevent the effects of monotony on singers. Rejected!!

Female preference hypothesis-predicts that males form leks because females like to visit large clusters of males consisting of a variety of potential mates from which she can quickly and safely compare the quality of her mating choices. ● You can compare males repertoire size to their reproductive success or you can look at the evolutionary history of a group to see if certain kinds of selection pressures consistently coincide with changes in repertoire size. Songbird phylogenies-as songbirds, passerines are distinguished from other orders of birds by the arrangement of their toes (three pointing forward and one back), which facilitates perching, amongst other features specific to their evolutionary history in Australaves. ● It seems likely that female choice has driven the evolution of male repertoires which are reliable indicators of male quality. ● It is often difficult to disentangle whether females prefer larger repertoires or whether they prefer certain song types that are more likely to be present in larger repertoires. ● It is unlikely that female selection for larger repertoires occurs in all species. ● It is possible for females to prefer larger repertoires even if large repertoires do not indicate male quality. ● Some female birds from non-repertoire species prefer repertoires but these preferences are latent until males evolve to sing more than one song type. Ability to match/not match. ● 2 hypotheses propose that song type repertoires do not merely function to increase variety but to give the option to match their rival songs. ● Song type matching can be facilitated by learning songs from your own neighbors or by settling in a neighbourhood where birds use song types that are in your repertoire. ● Singing a non matched song that was in the rivals repertoire was also an aggressive behaviour. This hypothesis was said to be unclear!!

Manage signal alignability-relies on a fundamental property of comparative choice: comparisons between structurally dissimilar things are less accurate than comparison between structurally similar things. This hypothesis was said to be unclear!! Different songs for different functions. ● All non-human communication systems including bird song lack several properties that characterize natural human languages. ● Low frequency sounds are useful in aggressive signals because only large individuals can produce them. ● Human language relies on a property called recursivity which allows an infinite range of expressions from a finite signal set. ● There is strong evidence that different song types can serve different functions. This hypothesis is supported!! Conclusion ● Sexual selection has driven song diversification. ● Sexual selection is a special kind of natural selection discovered by Charles Darwin. ● It is the process by which some kinds of individuals reproduce more than others. ● It is clear that song repertoires help males compete for mates with other males. ● We can also say with confidence that repertoires function differently in different species . ● Song repertoires are not like vocabulaires because animal communication is not like language. ● Birds cannot use song to place things because song is not an indefinitely flexible symbolic system. ● Great diversity of birdsong has evolved to mediate things like mates and territories. ● Natural selection does not drive animals communication systems toward human language. ● It shapes communication to meet each species needs for survival....