Reproductive ecology of temperate-nesting waterfowl : temporal and spatial patterns of investment and success in lesser scaup (Aythya affinis) (AYTHYA AFFINIS)
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Ecologists and conservation biologists alike aim to understand factors determining the abundance and distribution of free-living organisms and to pinpoint why free-ranging animal populations decline. My broad goals were to test ecological hypotheses related to timing of breeding and offspring survival in lesser scaup (Aythya affinis, hereafter scaup), a boreal-breeding diving duck species and to examine breeding-season explanations for why scaup populations remain below conservation goals. I demonstrated that timing of breeding and clutch size in scaup were remarkably consistent across a broad environmental gradient. Clutch initiation date was unaffected by growing season length (GSL) or latitude and was only marginally influenced by spring thaw date. Clutch size declined during the nesting season, but was unaffected by climatic variables. Although late-hatched ducklings (corrected for age and size) tended to have larger digestive systems, smaller leg muscles and lower abundances of intestinal parasites acquired through diet when compared with early-hatched individuals, timing of breeding did not independently influence duckling survival; survival declined seasonally only for ducklings raised by poor quality females. Assimilated diets of scaup ducklings were invariant with hatch date, and across a range of wetlands on two widely-separated boreal forest sites, duckling food densities did not vary throughout brood-rearing, nor did lipid content of amphipods. Taken together, my findings indicate that timing of breeding in scaup may have evolved to maximize temporal overlap between offspring and their critical food resources. Consequently, this species may be particularly sensitive to environmental changes that affect availability of prey, and I suggest that scaup conservation efforts should focus on determining how climatic factors influence invertebrate populations in key breeding areas. In addition, my study highlights the importance of maternal quality to reproductive success. Specifically, poor-quality female scaup may be unable to monopolize food resources as duckling densities increase throughout the season or may value their own survival more than that of their offspring as time constraints increase. Regardless of the exact mechanism, evaluating how changes in breeding habitat affect female quality could help to identify management actions that would facilitate recovery of scaup populations.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorClark, Robert G.
CommitteeChilton, Neil B.; Machin, Karen L.; Slattery, Stuart M.; Wiebe, Karen L.
Copyright DateMay 2012
timing of breeding