Avian botulism is a primary, year-round threat to adult survival in the endangered Hawaiian Duck (Anas wyvilliana) on Kaua‘i, Hawai‘i, USA

Adult survival is the most important demographic parameter influencing
population dynamics for many bird taxa. Thus, understanding how survival
probabilities and causes of mortality vary throughout the annual cycle is
critical for developing informed and effective management strategies. In
this study, we used radio-telemetry data to evaluate the effects of biotic
(e.g., sex, peak [September–April] vs. off-peak [May–August] nesting
seasons) and abiotic factors (e.g., rainfall, year, bi-monthly interval)
on adult survival, estimate annual survival probabilities, and identify
primary sources of mortality for Hawaiian Ducks (Anas wyvilliana), an
endangered, non-migratory dabbling duck, on the island of Kaua‘i, Hawai‘i,
USA over 2013 and 2014. Additionally, we used contemporaneous Hawaiian
Duck carcass recovery and surveillance data to examine temporal and
climatic associations with avian botulism outbreaks. Our results suggested
bi-monthly survival decreased with total rainfall during the preceding
two-month interval. Survival did not vary with sex, between peak and
off-peak nesting seasons, or between the two years of this study. Annual
survival probabilities (62–80%) were relatively low compared to the
closely related Laysan Duck (Anas laysanensis) on Laysan Island. Primary
causes of mortality included avian botulism and presumed predation by cats
(Felis catus). The botulism surveillance dataset revealed support for the
effect of rainfall on the number of sick and dead birds recovered (n =
216), with generally a greater number of recoveries during months with
middle-range total rainfall during the concurrent and preceding months.
Our study provides critical baseline demographic data for population
monitoring and highlights the importance of managing botulism risk and
non-native mammalian predators for the recovery of the endangered Hawaiian
Duck.