Effects of Spring Body Condition and Age on Reproduction in Mallards

Abstract: We explored predictive models relating body condition and age to nesting propensity, timing of nest initiation, clutch size of first nests, aggregated nest survival, hatching success, and timing of hatch in Mallards (Anas platyrhynchos). Nesting propensity had a positive linear relationship with body condition, and second-year (SY) females had a lower probability of nesting than after second-year (ASY) females (84% and 94%, respectively, at average body condition). Females in better body condition initiated nesting ~15 days earlier than those in poor condition, and SY females nested ~4 days later than ASY females at average body condition. Clutch size of first nests exhibited a curvilinear decline with body condition, such that large clutches were characteristic of females in the best condition that nested early. Nest survival and hatching probability were unaffected by body condition. Younger females had somewhat lower nest survival (11%) than older females (14%), which, in combination with renesting effort, resulted in an age difference in hatching probability (22% and 33%, respectively). Females in better condition hatched nests ~15 days earlier than those in poor condition, and SY females hatched nests ~4 days later, on average, than ASY females. Our results indicate that factors influencing the body condition of female Mallards arriving on breeding areas could influence subsequent reproductive investment and success. Condition effects are primarily through the mechanisms of nesting propensity, clutch size, and timing of nest initiation and hatch. Additionally, we provide evidence that Mallards in their first breeding season have lower reproductive potential than older females.