Factors influencing mortality of lesser scaup (Aythya affinis) ducklings during a West Nile virus outbreak / K.E.B. Gurney, R.G. Clark, and P.S. Curry.

Includes bibliographical references (pages 369-370).

Temporal variation in exposure and (or) susceptibility to disease-causing agents may result in changing disease risks
for offspring of seasonally reproducing organisms. Although increases in disease risk and disease-related mortality have been
observed during the course of the breeding cycle in some systems, the extent to which this is a generalized ecological pattern
remains uncertain. We obtained data during an outbreak of West Nile virus (WNV) associated mortality in 50 semicaptive Lesser
Scaup (Aythya affinis (Eyton, 1838)) ducklings and used known-fate survival models to assess whether daily survival rate (DSR) was
related to age, hatch date, immunogenic challenge, vector abundance, and risk ofWNVinfection. Ducklings produced late in the
breeding cycle had lower survival probabilities, relative to earlier conspecifics, but the best predictor of DSR was relative risk,
suggesting that reduced survival of late-hatched individuals may have been related to increasing exposure to WNV-infected vectors.