Effects of Food Abundance on the Timing of Breeding in Tree Swallows

Peter O. Dunn and Linda A. Whittingham

Department of Biological Sciences, UW-Milwaukee, pdunn@uwm.edu, whitting@uwm.edu

Understanding the mechanisms influencing the timing of reproduction has taken on new urgency as climate change is altering environmental conditions during reproduction, and there is concern that species will not be able to synchronize their reproduction with changing food supplies. In 2015 we completed the 19th year of study of the reproductive ecology of tree swallows at the UWM Field Station. One of our main goals is to determine how environmental factors, particularly temperature and food abundance, influence the timing of breeding and reproductive success. A prominent hypothesis predicts that reproductive success is maximized when animals synchronize their reproduction with seasonal peaks in food supply. This mismatch hypothesis does not seem to be supported in tree swallows, and many other species. Instead, reproductive success appears to be more closely related to the absolute levels of food, rather than to the timing of food. We thank Gretchen Meyer and Lou Nelson for their assistance, particularly in collecting data. This research was supported by funds from the College of Letters and Science, UWM.