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.

对于多数鸟类类群而言，成体存活率是影响种群动态的关键种群统计参数。因此，明确存活率与死亡原因在全年周期内的变化规律，对于制定科学合理且高效的物种管理策略至关重要。本研究借助无线电遥测（radio-telemetry）数据，针对美国夏威夷州考艾岛2013至2014年间的夏威夷鸭（Anas wyvilliana）——一种濒危的非迁徙性钻水鸭——评估了生物因子（如性别、繁殖旺季[9月至次年4月]与繁殖淡季[5月至8月]）与非生物因子（如降雨量、年份、双月间隔期）对成体存活率的影响，估算了年存活率，并明确了其主要死亡原因。此外，本研究还利用同期夏威夷鸭尸体回收与监测数据，探究了禽肉毒杆菌中毒（avian botulism）暴发的时间与气候关联因素。研究结果显示，双月存活率随前两个月的总降雨量增加而下降。存活率未随性别、繁殖旺季与淡季的差异，或是本研究的两个年份发生显著变化。与莱桑岛近缘物种莱桑鸭（Anas laysanensis）相比，本研究中夏威夷鸭的年存活率（62%~80%）相对偏低。其主要死亡原因包括禽肉毒杆菌中毒以及推测由家猫（Felis catus）造成的捕食。肉毒杆菌中毒监测数据集（样本量n=216）证实了降雨量对回收的病亡鸟类数量存在影响：在同期及前一个月总降雨量处于中等水平的月份，病亡鸟类的回收数量通常更多。本研究为种群监测提供了关键的种群统计基线数据，并强调了管控肉毒杆菌中毒风险与非本土哺乳类捕食者，对于濒危夏威夷鸭种群恢复的重要性。