Return to search

Population Regulation And Limitation Of The American Redstart (setophaga Ruticilla) During The Non-breeding Season

Conserving avian populations requires understanding how they are limited by density-independent factors and regulated by density-dependent processes. To better understand the relative importance of limiting factors and regulatory processes in wintering American Redstarts (Setophaga ruticilla), I carried out two related studies. First, to determine how food availability affects space use, body composition, and migration timing, I experimentally decreased food availability in high-quality mangrove habitat. Using an insecticide, I reduced food by ~80%, which mimicked natural losses in nearby scrub habitats. I found that food-reduced redstarts deposited fat and lost muscle compared to control birds. Subsequently, food-reduced redstarts experienced on average a one-week delay in departure on spring migration. Previous work has demonstrated that for each day delayed after the first male arrival on the breeding grounds, redstarts experience an 11% decrease in the chance of successfully reproducing. Thus, my results demonstrate experimentally, for the first time, that fluctuations in winter food-availability can lead to fitness costs for migratory birds, and that the mechanism involves a fat-muscle trade-off. Second, to understand how limiting factors and density-dependence interact to drive population dynamics, I used four years of data on redstarts wintering in Jamaican scrub and mangrove forests. In a dry and food-limiting year in scrub, I found that individuals on territories surrounded by a high density of conspecifics experienced large losses in food availability, suggesting a density-dependent depletion of resources. These losses in food were correlated with poor body condition, and individuals on high -density territories delayed departure on spring migration. In two wetter and less food-limiting years in scrub, and in all years in high-quality mangrove habitat, no effects of neighbor density were evident and density-independent factors alone appeared to determine body condition and departure date. Previous research has shown that poor body condition reduces annual survival and that delayed departure has carry-over effects into the breeding season, resulting in lower fecundity. Thus, both food limitation and neighbor density appear to drive population dynamics, but density-independent factors may override the negative effects of density when weather conditions are favorable. / acase@tulane.edu

  1. tulane:27857
Identiferoai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_27857
ContributorsCooper, Nathan W. (Author), Sherry, Thomas (Thesis advisor)
PublisherTulane University
Source SetsTulane University
LanguageEnglish
Detected LanguageEnglish
Format140
RightsCopyright is in accordance with U.S. Copyright law

Page generated in 0.0018 seconds