Acoustic adaptation in bird songs: A case study in cultural selection

Publication Year:
Usage 968
Downloads 968
Repository URL:
Crozier, Gillian
conference paper description
The greatest challenge for Cultural Selection Theory, which holds that Darwinian natural selection contributes to cultural evolution, lies is the paucity of evidence for structural mechanisms in cultural systems that are sufficient for adaptation by natural selection. In part, clarification is required with respect to the interaction between cultural systems and their purported selective environments. Edmonds, Hull, and others have argued that Cultural Selection Theory requires simple, conclusive, unambiguous case studies in order to meet this challenge. To this end, I am employing the songs of the Rufous-collared Sparrow, which seem to exhibit cultural adaptations that minimize signal degradation relative to local environments (Handford, et al.). Specifically, the more forested the habitat, the more the tail end of the song resembles a whistle rather than a trill; yet, variation in song is uncorrelated with genetic variation. I explore the mechanisms responsible for these putative acoustic adaptations through a series of computer simulations. I modify the framework of Alexander and Skyrms’ ‘Bargaining with Neighbours’: this dynamic evolutionary game theoretic framework is well-suited for my investigation because the local interactions between agents provide a basis for modeling song transmission from adults to fledglings. In the simplest version of the model, each bird adopts one of two song types – trill or whistle – and sings that song type for the duration of its life. These song strategies are communicated to other birds in neighboring territories, which are arranged as a grid composed of two acoustic habitats (forest and field). Birds have a set probability of dying in each year, and deceased birds are succeeded by fledglings. The likelihood that a fledgling adopts a particular song type depends on (i) the popularity of a particular song-type among neighboring birds and (ii) the relative ‘audibility’ of each signal, which is a joint function of the habitat and song type of the signaling bird. The main point of this research is not to test this model, but to demonstrate that models of this type have the resources to meet the outstanding challenges in Cultural Selection Theory. The benefits of this research are threefold. First, it will lend much needed empirical support to Cultural Selection Theory by clarifying the nature of the interaction between culture and environment. Second, it will support Alexander and Skyrms’ work by providing a set of empirically testable consequences for their model. Finally, it will contribute to evolutionary theory by clarifying the scope and limits of adaptation by natural selection.