The social factor in song learning in american sparrows  (Page 2/9)

In this chapter, we will focus on four species of American sparrows (family Emberizidae). We will cover recent theories and findings regarding why song learning occurs, who songs are learned from, when (i.e. at what stages of development) songs are learned, and how songs are learned, while focusing on the social factors involved. [link] and [link] describe the species of sparrows covered.

Why do they learn? – the adaptive function of song learning

Songs are an important communicative tool for songbirds, but do they make sense as an evolutionary adaptation? It seems that all of the costs associated with song learning, such as time and energy (which can be diverted towards foraging, for instance), can be avoided if songs are completely innate , like a cricket chirp. From an evolutionary point of view, it follows that song learning can only evolve if its benefits outweigh these costs.

So what are these benefits? Learning is usually a tool used when external circumstances are variable, because it has the potential to help individuals adapt their behaviors to changing environments. For example, humans have the ability to learn languages, which is beneficial when a baby is born into a country that does not speak the language of its parents or when a person moves to a country that speaks a foreign language. Therefore, songs are most likely an important tool used by songbirds to adapt to their changing social environments. Examining differences between sedentary and migratory white-crowned sparrows in song learning from neighbors illustrates this concept. The songs migratory birds learn from tutors are more plastic , while the songs sedentary birds learn are more accurate (Nelson et al. 1995). Such differences may be explained by the fact that migratory birds have more uncertainty in where they will breed. Therefore, their songs remain more plastic, allowing the birds to easily adjust their songs to those of their neighbors where they decide to breed (Nelson et al. 1995). See Sharing Hypothesis of Song Learning below on advantages of adjusting songs to those of neighbors. More on the role of neighbors as song tutors will be discussed in a later section.

The importance of social learning can be explained by two hypotheses: the repertoire hypothesis and the sharing hypothesis (Beecher&Brenowitz 2005).

Repertoire hypothesis of song learning

The repertoire hypothesis states that song learning allows birds to acquire a large song repertoire , which aids them in attracting mates, since females prefer males with large repertoires (Searcy&Anderson 1986). Gil and Gahr (2002) explain that song repertoire is an honest communication and can be used for sexual selection because it directly correlates with the amount of neural space in an individual, which is a measure of intelligence in songbirds. However, this hypothesis has been under much criticism, as most birds have just a few songs; many have just one. To explain this observation, Garamszegi (2004) claims that limited neural space acts as a strict limitation to the size of song repertoire. Therefore, the cost of having a large repertoire (taking up neural space) balances the benefit (attracting females).