Avian Conservation and Ecology (Dec 2022)
Hydrology management influences nest survival but not clutch size in Lesser Scaup
Abstract
Components of reproductive success such as clutch size and nest survival may greatly affect avian population growth rates. Understanding how environmental conditions influence temporal variation in these demographic parameters could thus provide valuable insight into best management practices for species of concern. One such species that could benefit from a better understanding of such processes is Lesser Scaup (Aythya affinis), whose overall abundance in North America has declined since the early 1980s. We used a long-term study (2005–2019) of Lesser Scaup demography at Red Rock Lakes National Wildlife Refuge in southwestern Montana, USA, to examine how the management of wetland conditions influenced within- and across-year temporal variation in clutch size and nest survival. Predicted clutch size varied more across nest initiation dates (6.18–10.05 eggs) within years than it did across years (7.51–8.38 eggs), and none of the covariates we examined were significantly related to clutch size across years. Nest daily survival rates varied substantially across days within breeding seasons (e.g., 2018: 0.38–0.985), and annual mean nest survival varied greatly across years (0.27–0.58). Furthermore, seasonal chronology of managed wetland water levels influenced nest survival such that years when water levels gradually rose to a maximum late in the breeding season, relative to mean nest initiation date, resulted in the highest nest survival. These findings collectively suggest that when flows can be manipulated with water control structures, efforts to manage the chronology of water levels at watershed and local wetland scales could improve nest survival, whereas such management efforts will not likely affect clutch sizes.
