Comparative reproductive ecology of female buffleheads (Bucephala albeola) and Barrow's goldeneyes (Bucephala islandica) in central British Columbia

Waterfowl (Anseriformes) generally have high energetic costs for reproduction because they lay large, energy-rich eggs. Consequently, many temperate nesting ducks (Anatinae) occupy seasonally productive environments to meet nutritional requirements for egg production. However, ducks in the genus Bucephala often breed in unproductive boreal and montane regions. This study was conducted to investigate nutritional aspects of reproduction in female Buffleheads (Bucephala albeola) and Barrow's Goldeneyes (Bucephala islandica) breeding in central British Columbia.; Diet composition of breeding female Buffleheads and Barrow's Goldeneyes, which consisted primarily of benthic insects, was similar, providing support for the food defense hypothesis as an explanation for evolution of fixed space territorially in the genus Bucephala.; Mean egg laying interval ({dollar}pm{dollar}SE) for Buffleheads was 48.36 {dollar}pm{dollar} 2.35 hr. which was similar to that of Barrow's Goldeneyes that laid, on average, every 45.32 {dollar}pm{dollar} 1.40 hr. As a consequence of slower rates of egg production, daily energetic costs of reproduction in female Buffleheads and Barrow's Goldeneyes, evaluated relative to their basal metabolic requirements, are among the lowest documented for ducks.; Patterns of lipogenesis differed between female Buffleheads and Barrow's Goldeneyes, but both species catabolized somatic fat for egg production. Buffleheads maintained stable body protein during reproduction, and thus relied exclusively on dietary protein for clutch formation, whereas Goldeneyes catabolized small amounts of somatic protein to produce egg protein in 1993. Use of body protein by a primarily carnivorous duck suggests that protein availability, i.e. invertebrate abundance, in breeding habitats used by Goldeneyes was periodically deficient. Somatic mineral supplied approximately 8% of clutch minerals in Buffleheads and 3% of clutch minerals in Goldeneyes during the 1993 breeding season, but neither species used endogenous minerals for eggshell production in 1994.; Size of lipid and protein reserves did not limit clutch size in either Buffleheads or Barrow's Goldeneyes. Furthermore, clutch size was negatively related to somatic mineral mass in Buffleheads, but positively related to clutch size in Barrow's Goldeneyes. Thus, from a nutritional perspective, only mineral availability limited clutch size in Barrow's Goldeneyes, whereas relatively low rates of somatic tissue catabolism suggested that nutrient availability may not constrain clutch size in Buffleheads.