Naturally Occurring Constraints on Development in a Model Learning System

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Scientific Merit: The use of complex acoustic signals for communication is widespread in animals. In songbirds, such vocal signals are called 'song' and have an additional, intriguing aspect in that they are learned. How birds learn and develop their songs is an important model used for studying the evolution, ecology and neuro-physiological bases of learning in general. However, our understanding of this model is limited because most studies of song learning in birds have been based on laboratory experiments in which essentially all ecological and social variables have been controlled or removed. Recently, it has become increasingly evident that the complex social and ecological factors songbirds experience in nature can affect the course of development and produce a pattern different from that observed in the lab. Past studies of brown-headed cowbirds demonstrate this point very clearly. In the lab, cowbirds follow a developmental pathway that results in young males singing adult songs by the time they are one year old, as is the case in many other songbirds. Field studies, however, show that most cowbirds take two years to develop an adult repertoire in the wild. It has been hypothesized that the extended song development observed in cowbirds is due to the combined effects of two constraints. The first occurs during a bird's hatching year and is a restricted, or even complete lack of, exposure to local songs because adults are no longer singing by the time many juveniles are old enough to be memorizing local songs. The second is the apparent inability of young males to alter their song repertoires during their first breeding season because of naturally elevated levels of testosterone. The present project continues investigations into these natural constraints on song development in male cowbirds and also, on the development of female song preferences. The proposed research will make significant contributions to understanding of the birdsong model, arguably the pre-eminent model system for experimental studies of learning, by: 1) Maximizing the utility of the birdsong model by determining the normal course of development in nature and by identifying factors that have and continue to shape evolution of song learning, 2) Elucidating the nature of sensitive periods, which are an important characteristic of language acquisition, imprinting and development of normal sensory function, 3) Determining whether high testosterone levels are the proximate cause of the loss of behavioral plasticity during the breeding season, 4) Exploring the developmental bases of female preferences for variants of male song. The last objective is particularly important because although it is generally accepted that one of the prime functions of song in birds is attraction and sexual stimulation of females, little is known about the ontogeny of female preferences even though bird song is a major model system for studies of sexual selection. Broader Impacts: The project will result in salaried training for graduate and undergraduate students. In addition, the research will used to educate the public about avian breeding biology, including cultural and genetic evolution. Results will also be incorporated into a University of California outreach program for elementary school students. Because the study species, the brown-headed cowbird is involved in the decline of several other bird species and is managed heavily in some regions of the US, the research may contribute to management efforts for endangered species.