Delayed Dispersal: Teasing Apart the Effects of Resources and Parents

Cornell University, Ithaca NY

Investigators

Abstract

In birds, as in humans, young sometimes remain at home with their parents long after the usual age of independence. In human agricultural societies, it is usually males, particularly first-born sons, that remain at home and the extent of family wealth, measured as farmland, is a key factor. Males also tend to be the gender that stays home in birds and this leads to a variety of interesting consequences, including cooperative breeding, where sons provide aid by feeding chicks in their parents' nest, or less obvious social behaviors such as communal roosting, cooperative defense of the territory, and food-sharing by family members. Like humans, western bluebirds ?own? land in the form of defended territories with mistletoe, which provides a continuous supply of berries over the winter. Like farmers, the bluebirds ?plant? the seeds of mistletoe by passing the berries through their guts, leaving the seeds still viable and surrounded by a sticky coating that helps them to adhere to limbs and grow. Western bluebird sons and some daughters tend to stay home with their parents during their first year of life. When mistletoe abundance was reduced by half, fewer sons stayed home, suggesting that in western bluebirds, as in humans, wealth plays a role in delayed dispersal. The current work will determine whether parental favoritism also provides advantages to sons staying at home and whether in staying, sons incur fitness costs in the form of increased competition with relatives, genetic costs of reduced offspring viability due to incest, and reduced mate availability due to incest avoidance. Studying these factors will complete the picture of delayed dispersal for western bluebirds and help tease apart which is more important to sons staying home ? resources or the increased access to those resources that comes from living with nepotistic parents. It will also establish the extent to which mistletoe is a keystone resource that is critical for western bluebird conservation.