Winter temperatures limit population growth rate of a migratory songbird.
Understanding the factors that limit and regulate wildlife populations requires insight into demographic and environmental processes acting throughout the annual cycle. Here, we combine multi-year tracking data of individual birds with a 26-year demographic study of a migratory songbird to evaluate the relative effects of density and weather at the breeding and wintering grounds on population growth rate. Our results reveal clear support for opposing forces of winter temperature and breeding density driving population dynamics. Above-average temperatures at the wintering grounds lead to higher population growth, primarily through their strong positive effects on survival. However, population growth is regulated over the long term by strong negative effects of breeding density on both fecundity and adult male survival. Such knowledge of how year-round factors influence population growth, and the demographic mechanisms through which they act, will vastly improve our ability to predict species responses to environmental change and develop effective conservation strategies for migratory animals.
Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
Bradley K
BK
Woodworth
Department of Biology, Bowdoin College, Brunswick, Maine 04011, USA.
Nathaniel T
NT
Wheelwright
Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
Amy E
AE
Newman
Swiss Ornithological Institute, Sempach CH-6204, Switzerland.
Michael
M
Schaub
Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
D Ryan
DR
Norris
D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D001947:Breeding; D017753:Ecosystem; D005260:Female; D005843:Geography; D062312:Islands; D008297:Male; D009509:New Brunswick; D011156:Population Density; D011158:Population Growth; D012621:Seasons; D020308:Songbirds / Q000502:physiology*; D013696:Temperature; D014887:Weather