Novel pathogens, climate, and continental populations


Storm on the Pacific Ocean near San Diego, California.

Storm on the Pacific Ocean near San Diego, California.

Continental impacts of disease and climate on North American birds

West Nile virus affects species across a wide variety of taxa.  I examined its influence on survival rates of 49 bird species (George, Harrigan, LaManna et al. 2015 Proceedings of the National Academy of Sciences).  As co-first-author of the study, I conducted all analytical work, which involved mark-recapture data for nearly 300,000 individual birds over 16 years from over 500 bird-banding stations across North America.  Spatially- and temporally-explicit survival models showed that West Nile virus reduced annual survival for 23 of 49 species (47%), but the virus had long-lasting impacts on some species and only temporary effects on others.  Thus, immune responses to West Nile differed widely among bird species, suggesting that defensive responses vary among hosts when faced with a generalist pathogen.

Global climate cycles, like the El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO), are sensitive to a warming climate and may synchronize demographic rates of a wide variety of species at continental scales.  We tested for effects of global climate cycles on annual survival of 49 bird species across North America.  Annual survival for 29 out of 49 species (60%) varied significantly with either ENSO or NAO.  These results suggest that global climate cycles synchronize population demographics at broad geographical scales.  These effects are also critical to understand given that climate change is projected to intensify both the ENSO and NAO climate cycles.

Sunset on Humboldt Bay Wildlife Refuge, Arcata, California.

Sunset on Humboldt Bay Wildlife Refuge, Arcata, California.