Proximate and ultimate control of reproductive effort in northern shovelers (Anas clypeata) nesting at Minto Flats, Alaska

Abstract

The purpose of this study was to examine factors that influence reproductive effort of female Northern Shovelers (Anas clypeata) nesting at Minto Flats, AK during summer 1991-1993. I investigated the importance of endogenous nutrient reserves to females during egg production and examined changes in organ weights and intestine lengths through the reproductive cycle. Changes in organ weights and intestine length were similar to those of shovelers nesting in Manitoba. Females used neither somatic lipid reserves, protein reserves, nor mineral reserves to produce eggs. Individual variation in somatic lipid reserves was explained by body size and nest initiation date, while variation in somatic protein reserves was explained by standardized nest initiation date. Somatic mineral variation was explained by differences among years. Neither somatic protein nor mineral reserves were reduced during incubation, but somatic lipid reserves decreased significantly. I conclude that endogenous nutrient availability does not proximately limit clutch size during laying for this population, possibly due to high productivity of interior Alaska wetlands and long days. Little is known about nest attendance behavior of ducks in the subarctic; therefore, I examined shoveler nest attendance patterns at Minto Flats to determine if observed patterns differed from those documented for shovelers nesting in Manitoba, Canada. Shovelers nesting at Minto were less attentive and took more frequent, longer recesses than shovelers in Manitoba. I examined patterns of nest attendance during incubation in relation to clutch volume and female weight loss to determine if females make tradeoffs between energy invested in the clutch and energy invested in incubation. I found no evidence of energetic tradeoffs by Shovelers nesting at Minto Flats. To determine if the trait of synchronous hatching could limit clutch size for a species of the genus Anas I measured development time and metabolic rates of Mallard (Anas platyrhynchos) eggs incubated in a constant environment. Females varied in length of time their eggs required to reach the star-pipped stage of hatch. Metabolic rate of eggs varied positively with position in the laying sequence and varied among females. These results indicate that metabolic rate may act as a synchronization mechanism for hatch.