Does Age, Residency, or Feeding Guild Coupled with a Drought Index Predict Avian Health during Fall Migration?

Abstract

Birds are good indicators of environmental change and are often studied for responses to climate. Many studies focus on breeding birds, while fewer look at the migration period, which is a critical time for many birds. Birds are more susceptible to unusual climatic events during their migration due to the metabolic stress of long-distance movements. In the fall of 2020, an unusual cold weather event coupled with drought and wildfire smoke led to a large avian mortality event in New Mexico. Later analysis pointed to the mortality being largely due to starvation. This was the impetus for our research. We used 11 years of fall bird banding data from two locations, along with local drought indices, to determine what predicts avian health during the migration period. We used fat score data from over 15,000 individual birds to assess whether drought indices, age, diet, or residency influenced avian health using multiple logistic regression. We found that the probability of positive fat scores decreased as drought severity increased for younger, insectivorous, migratory birds. Insectivores had a higher probability of receiving a fat score greater than zero relative to local drought conditions, which is important, since many North American insectivores are in steep decline. Migratory birds showed a greater response than year-round residents, and older birds showed a lower but significant response compared to hatch-year birds. Our results suggest that migratory insectivores in the southwestern United States may be less resilient to drought-related climate change.

Flexible migration and habitat use strategies of an endangered waterbird during hydrological drought

“…Drought influences the distribution of species, biodiversity, and net primary productivity of both terrestrial and aquatic ecosystems (Clark et al, 2016;Tilman & Haddi, 1992;Walls et al, 2013). For avian communities, specifically, drought can influence individual body condition and behaviors (Anderson et al, 2021;Stanek et al, 2022), population abundance and demography (Chan, 1999;Mooij et al, 2002), and avian species richness (Albright et al, 2010). Waterbirds, bird species reliant on surface water to meet all or most of their lifecycle events, are especially vulnerable to hydrological drought (i.e., a reduction in surface and groundwater; Van Loon, 2015).…”

The effects of environmental conditions on eggshell thickness of two North American secondary cavity-nesting birds

“…Passerines are good indicators of ecosystem health due to the high rate of monitoring in many parts of the world and their sensitivity to environmental conditions (Gregory et al 2003, Sousa et al 2008, Gregory and van Strien 2010, Smits and Fernie 2013). In September 2020, there was a mass mortality event involving hundreds of thousands of migratory songbirds in the United States after a cold front moved through the Southwest (Stanek et al 2022). These birds likely succumbed to emaciation after the combined effects of drought, wildfires, and lack of food resources along their migration corridors (Yang et al 2021).…”