|dc.description.abstract||Variation in avian reproductive success (RS) can be influenced by intrinsic traits (e.g., individual quality, physiology and experience) or extrinsic factors (e.g., weather, habitat use, or landscape composition) which can act across multiple scales. Determining how these two factors affect RS – and how they interact – represent significant challenges for ecologists and conservationists. Thus, I evaluated these two main hypotheses using information obtained for northern pintail (Anas acuta) and mallard (Anas platyrhynchos) breeding in the Canadian prairies. I integrated data from laboratory experiments, field-based observational studies and existing long-term datasets to determine the relative importance of intrinsic (past and current metrics of individual quality) and extrinsic (landscape composition) factors in contributing to variation in RS for prairie-breeding ducks at multiple scales. I also validated and used feather biomarkers to investigate evidence of energetic carry-over effects on reproductive performance in both species.
To verify that an individual’s feather corticosterone (CORTf) levels are related to energy expenditure, I manipulated work rates of mallard ducklings in the laboratory. Ducklings experiencing higher workloads had lower body mass, slower growth rates, greater daily energy expenditure and higher CORTf. These patterns were repeatable and CORTf reflected current energetic demands during feather replacement.
Using CORTf and stable isotopes in feathers, I provided new insights regarding the consequences of migratory origins of adult female pintails breeding in southern Saskatchewan, and found no evidence of strong carry-over effects on pre-breeding body condition or reproductive investment. However, late-nesting females were typically from coastal wintering regions and had higher CORTf in body feathers grown during winter-spring, suggesting that energetic challenges during body moult during late winter or early spring migration delayed timing of breeding.
I investigated maternal influences on RS and found that pintail duckling survival was higher among breeding females with lower late-incubation body mass, those that hatched nests somewhat later in the season or behaved more cautiously during brood rearing. Extrinsic landscape conditions drove most variation in duckling survival. Duckling survival was higher in grassland-dominated landscapes and, in agricultural landscapes, broods hatching from winter wheat had similar survival to perennial cover, double the estimates in spring-seeded cropland. Ducklings raised in local environments with higher amounts of perennial cover and seasonal wetlands, but lower amounts of wetland edge, had higher survival. On balance, the benefits of higher nest survival in winter wheat were not completely superseded by lower duckling survival for broods raised in intensive agricultural areas.
Using unique data sets composed of individually-marked adult female mallards, I did not find any consistent indication that CORTf was correlated with either reproductive effort or success, or local weather and wetland conditions, in the same year as feather growth. Counter to initial predictions, I found that current RS was unrelated to CORTf levels in feathers grown the previous summer-fall. Path analyses of mallard breeding decisions revealed that lighter females were less likely to breed but experienced higher hatching and fledging success; female age had no direct effects on the decision to breed nor directly influenced fledging success. As expected, greater nesting effort and investment occurred on sites with a higher pond abundance and above-average regional pond conditions.
For breeding mallards, heavier females were more likely to settle in areas with above-average pond conditions, nested earlier and re-nested more often while females that had lower CORTf in wing feathers tended to re-nest more often but experienced higher nest success. Older birds, and those that settled in areas with more grassland, had larger clutch sizes. As expected, nest success was higher on sites with a higher abundance of ponds and above-average regional pond conditions but lower for early and re-nests, with the number of hatched young smaller for late or re-nests. Overall, fledging success was higher in late-hatched or larger broods and of successful nests, more ducklings fledged if it was a re-nest but there were trade-offs with pond abundance and egg production.
Overall, in pintails and mallards, local environmental factors and landscape composition had consistently strong effects on RS whereas measurements of individual quality were generally weaker or more variable. Through integration of intrinsic and extrinsic factors, I bridged our understanding of variation in energetic conditions and RS across ecological, spatial and temporal scales. Further study is required to evaluate the roles of carry-over effects on prairie-breeding ducks, as this would more clearly reveal putative linkages between conditions on non-breeding areas and subsequent RS.||