Professor University of California, Los Angeles Los Angeles, California, United States
Abstract: Climate change is causing severe and wide-ranging impacts on organisms worldwide, including population declines and extinctions. The unique biology of birds makes them vulnerable to climate warming in complex ways: birds are endothermic as juveniles and adults but also have ectothermic life stages (eggs, and in some species, nestlings) whose exposure to temperature variation depends on adult incubation behavior. A mechanistic framework for evaluating these stage-specific effects of temperature variation is key to capturing this complexity and making reliable predictions about bird population responses to climate change. Such predictions are critically important for managing bird populations, especially given recent dramatic declines. In this talk, we present a mathematical model of bird population dynamics that incorporates the effects of temperature on avian vital rates in a mechanistic and stage-structured framework. We analyze this model to examine the effects of seasonal temperature variation and climate warming on bird population dynamics with different suites of life history traits.
We report three key findings. First, sensitivity of the endothermic stages to hot extremes impacts incubation behavior, which in turn affects the maturation and death rates of the ectothermic stages. Second, faster egg maturation due to hot extremes has a strong effect on bird population dynamics, leading, in some cases, to low abundances that predispose populations to extinction. Third, warming can impact not only average population abundance, but can also generate unstable oscillations that create interannual variation in abundance for birds with certain life history traits. In ongoing work, we investigate IPCC predictions on warming to investigate the hypothesis that increases in mean temperature are more detrimental to the more warm-adapted southerly populations, which have narrower thermal tolerance ranges, while hot extremes are more detrimental to the more cold-adapted northerly populations.
