Breeding Season Ecology and Demography of Lesser Scaup (Aythya affinis) at Red Rock Lakes National Wildlife Refuge

摘要

It is hypothesized that individuals make reproductive decisions based on current assessments of their physiological condition and environmental conditions. For female lesser scaup (Aythya affinis), breeding occurs after an energetically costly spring migration. Increasing fat reserves (i.e., 'body condition') prior to breeding allows a female to produce a larger clutch of eggs, but time spent gaining body condition is costly in terms of time allowed to raise ducklings before freezing conditions in the fall. In Chapter 2 I explored rate of pre-breeding body condition gain in female lesser scaup, and how that rate influenced clutch size. Spring phenology, measured by proxy as water temperature, and water depth strongly influenced the rate at which females increased body condition. Early springs with low water levels led to greater rates of body condition gain in female scaup. The higher the rate of body condition gain, the larger the clutch of eggs females produced. Body condition is also an important determinant of breeding in female ducks; females in poor body condition are more likely to forego breeding. I explored how body condition, wetland conditions, and prior experience influence a female's decision to breed in Chapter 3. Body condition was a strong determinant of when a female bred, with females in good body condition breeding earlier than females in poorer body condition. Habitat conditions were also important, with drought reducing the proportion of breeding lesser scaup females. In Chapter 4 I examined survival costs of reproduction in female scaup. Nesting exposes females to increased predation risk (a concurrent survival cost), and reduced post-breeding body condition may reduce female survival the subsequent non-breeding season (a serial, or 'downstream', survival cost). Female survival during breeding and non-breeding seasons was most correlated with breeding season water level on the study site, but in opposite directions. Breeding season survival increased with increasing water levels, while non-breeding season survival declined. High water levels on the study site increased the availability of presumably high-security nesting habitat, and also increased female reproductive effort. The former increased breeding season survival, while the latter reduced non-breeding season survival.