Understanding relations between breeding bird species and extreme weather

Extreme weather events are increasing in frequency due to climate change. Extreme weather events like periods of drought or cold snaps may impose hardship on many animal and plant populations. However, little is known about biotic response to extreme events. For example, some species experience population size changes in association with extreme weather, and some do not. However the mechanisms responsible for observed declines in avian abundance following heat waves and drought are not clear. Our goal was to characterize the population changes of North American bird species in relation to temperature and precipitation extremes using North American Breeding Bird Survey (BBS) data. We derived standardized measures of extreme precipitation and air temperature based on phase 2 NASA Land Data Assimilation System (NLDAS-2), an hourly 1/8 degree resolution land surface forcing dataset, and modeled population responses, during the breeding season, of 363 bird species. Of those species in which a change was observed, many demonstrated decreases in total population size, suggesting either mortality or reproductive failure (or both) are the causative mechanisms of this decline. A greater proportion of population changes were associated with extreme conditions in the same year than in the previous year. Some species exhibited population decreases in areas of extreme weather and increases in areas with environmental conditions more favorable to breeding while overall abundance remained relatively constant, which might indicate movement. The patterns of bird population changes in relation to extreme weather events provide insight for planners as they consider modifications to our national protected area network that will limit threats posed by climate change to bird populations.