| Summary: | Annual rates of productivity in wildlife populations are influenced by climatic and biotic factors, and offspring production and recruitment are key components of population growth in many duck species. For lesser scaup (Aythya affinis; scaup), a species of conservation concern, productivity can be particularly influential to population growth, although our understanding of factors affecting production is incomplete. I sought to identify local drivers of productivity in scaup and several other duck species by testing hypotheses related to: (i) spring phenology; (ii) local breeding-season weather; (iii) density dependence; and (iv) predator-prey dynamics. To test these hypotheses, I used long-term datasets from two distinct breeding areas: a montane site at Red Rock Lakes (RRL) Montana, USA, and a boreal site, the Yellowknife Study Area (YKSA) near Yellowknife, Northwest Territories, Canada. Ducks breeding at these sites have been studied for periods of 9 (RRL, scaup) to 26 (YKSA, multiple boreal duck species) years. I used age-corrected body masses of 5727 scaup ducklings at RRL and 26 years of annual duck pair and brood abundance counts at YKSA to assess annual variation in duckling quality (RRL) and productivity (YKSA). Age-corrected scaup duckling body mass was lower in years of both early and late spring conditions (i.e., ice-out dates) at RRL. There was no effect of the timing of spring conditions on brood abundance at YKSA. Warmer local weather conditions in the pre-nesting period were positively associated with metrics of duckling quality (RRL) and productivity (YKSA). Brood-rearing weather conditions had a small positive relationship with duckling quality at RRL, but no relationship was found with brood abundance at YKSA. I also related scaup duckling quality to the density of conspecifics at RRL. Age-corrected body mass of scaup ducklings was lower in years of higher duckling density, a pattern that is consistent with possible density dependent regulation of scaup productivity at this site. At YKSA, ...
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