LTREB: The Ecological and Organismal Basis for Early-Season Life History Variation in Tree Swallows Tachycineta Bicolor

Cornell Univ - State: Awds Made Prior May 2010, Ithaca NY

Investigators

Abstract

This project is to extend and upgrade a long-term study of the ecology and reproductive biology of tree swallows (Tachycineta bicolor) nesting near Ithaca, New York. This population numbers approximately 300 breeding pairs. The population has been studied for the past fifteen years, and a large number of techniques have been developed to efficiently explore tree swallow biology and ecology. Many of these techniques take advantage of the fact that tree swallows readily nest in artificial nest-boxes. Like many other songbirds, tree swallows have about a 50% annual survival rate, so a five year study can sample many birds during their entire reproductive lifetimes. Tree swallows are obligate aerial insectivores. Thus, they are unusually sensitive to short-term changes in weather, because their prey, flying insects, are unable to fly during cool temperatures or rain. Previous research has developed the methods for sampling and analyzing insect availability on a daily basis. One of the principal foci of the research in Ithaca in the past ten years has been investigating the seasonal decline of clutch size. Earlier laying females lay larger clutches, and they pay no measurable cost for laying earlier. Tree swallows across North America have advanced their date of laying, apparently in response to global climate change, and understanding the determinants and consequences of lay-date variation is thus of both basic and applied interest. The current project would attempt to answer three related questions: 1) How does variation in insect abundance and weather affect the lay-dates of individual swallows? 2) Does variation in flight performance correlate with variations in lay-date and chick-provisioning performance? 3) What are the consequences of short-term variation in weather and food supply both in terms of organismal biology and breeder fitness? Flight performance is clearly a critical trait for an aerial insectivore, and it will be evaluated in a Flight Performance Test Tunnel that is already constructed and in need of only slight modifications. Chick-provisioning performance will be assessed through a series of detailed behavioral observations coupled with samples of the food being delivered to the chicks collected in a specially developed trap. Physiological health and stress will be evaluated with repeated measurements of blood characteristics. This project would bring a new level of detailed measurements to a long-term study that has proved its worth both in basic research output and in education of students at all levels. By studying swallow reactions to the dynamic weather conditions of a temperate ecosystem, we can better understand the relationships between an animal's biology and its environment, both today and in the past, and make better predictions about how environmental changes will affect animal populations.