Abstracts

Presented by David Johns - Email: david.johns@usask.ca

Drivers of variation in waterfowl reproductive success can broadly be grouped as restraints by an individual (i.e., breeding decision), constraints imposed from within individuals (i.e., intrinsic quality/condition) or from the surrounding environment (i.e., extrinsic or environmental quality). The simultaneous contributions of both intrinsic and extrinsic factors across seasons complicates investigations interested in disentangling relative effects of reproductive or survival trade-offs for migratory waterfowl. We used a combination long-term mark-recapture datasets, hormone biomarkers and large-scale studies of mallard reproductive success across the Prairie-Parklands. We used structural equation modelling to evaluate how current and antecedent factors influenced reproductive success while simultaneously assessing contributing factors to individual reproductive performance (fledging success). Path analysis indicated that neither amount of grassland nor past energetic condition were important to determining reproductive decisions but above-average pond abundances attracted females with higher body mass, greater nesting propensity and reproductive investment. Females in areas with higher wetland abundance were more likely to breed and made larger investments in nesting but produced fewer fledged ducklings. Intrinsic female traits had opposing influences on nest investment and reproductive success with age related trade-offs between breeding likelihood and ultimate success. We found evidence that late-nesting (re-nesting) females were more likely to fledge duckling(s) but had smaller brood sizes relative to early nests and females that laid more eggs in a season indirectly fledged more offspring (i.e., through greater hatching success and brood size at hatch) and yet the negative direct path between egg production and fledging success implies a cost associated with investment. Simultaneous consideration of both intrinsic quality, reproductive investment and environmental constraints enables more detailed understanding of reproductive ecology and potential carry-over effects.