Interactions among climate, stress, and avian influenza virus infection, and their impacts on survival in migratory waterfowl

Abstract

Wildlife are increasingly faced with the need to adapt or respond to climate change, altered habitats, and emerging infectious diseases. In birds, responses to stressors are mediated by corticosterone (CORT). Though beneficial in life-threatening situations, chronic stress can be energetically costly, negatively impacting disease susceptibility, condition, reproduction, and survival. Waterfowl are natural, asymptomatic reservoirs of low pathogenic avian influenza viruses (LPAIVs), and few studies have demonstrated a cost to infection, showing impacts on body condition and timing of migration. I examined relationships among climate, stress, body condition, and AIV infection, and how they interact to influence survival in migratory waterfowl. Data subsets were selected from >7000 Blue-winged Teal (Spatula discors) sampled in the Canadian prairies prior to fall migration, from 2007-2018. Feather CORT (CORTf) an integrated measure of energy expenditure during the moulting period increased in response to increasing mean daily standard deviation of temperature during feather growth (early July), which carried over to impact subsequent body condition index (BCI) and mass in August. Carry-over effects on BCI were more prominent in females compared to males, and females had a higher mortality rate, based on mark-recapture analysis using band recovery data. Mortality was not, however, associated with CORTf, BCI, or mass. Males with higher CORTf were less likely to be hunted within the first year, suggesting CORTf provided an advantage to males by helping them avoid being hunted, or a lower proportion of males with high CORTf were present in the population, resulting from increased mortality or failure/delay in migration prior to subsequent hunting seasons. AIV did not appear to pose a cost to Blue-winged Teal, as it was not associated with CORTf, BCI, mass, or survival. The study demonstrated a complex, non-linear relationship between AIV infection and climate; the probability of infection was negatively associated with mean daily minimum temperatures 3-10 days prior to sampling up to ~10⁰C, and was positively associated with mean daily minimum temperatures above 12°C. This relationship is likely a reflection of temperature on environmental AIV survival, as well as on waterfowl behaviour, distribution, and movement, affecting local population densities and opportunities for transmission. My results provide insight into complex relationships among climate, stress, condition, AIV infection, and survival in migratory waterfowl.