Feeding Ecology of Ring-Necked Ducks in Northwestern Minnesota

Feeding ecology of ring-necked ducks (Aythya collaris) was studied in northwestern Minnesota, from April to August 1978-80. Adult male and female diets were similar throughout reproduction. Food use by adult birds before recrudescence of female gonadal tissue varied by habitat: diets for birds using temporary wetlands were dominated by plant material, whereas animal foods made up one-half of the diet of males and females collected on semipermanent and permanent wetlands later used for nesting. The proportion of invertebrates consumed by adult birds increased after the arrival period. Female reproductive protein requirements are drawn primarily from the diet during prelaying and laying. Based on estimated consumption rates, females may feed up to 19 hours/day to obtain required protein. Consumption of invertebrates by nonlaying birds suggests that their use can be energetically profitable; however, food selection by prelaying/laying hens on a noncaloric basis (e.g., minerals) may result in expenditure of fat reserves. Juveniles ate mostly invertebrates, but the proportion of animal material in the diet differed between ageclasses. Although significant food preferences were exhibited by adults and juveniles, availability played a prominent role in food selection. Food habits of adult and juvenile ring-necked ducks appear to be more generalized than those of congenerics, but there is considerable overlap in the food taxa consumed by diving ducks (Tribe Aythyini). J. WILDL. MANAGE. 49(3):546-557 Energetic costs of gonadal growth for female ducks and geese are large relative to those of other major groups of birds (King 1973, Ricklefs 1974). Among waterfowl, dependence on breeding ground food resources for reproductive energy and nutrient requirements varies by species and group. Whereas Arctic nesting geese and common eiders (Somateria mollissima) are essentially independent of food resources from arrival on the breeding grounds through incubatio by virtue of reserves accumulated on wintering and staging areas (Korschgen 1977, Ankney and MacInnes 1978, Raveling 1979), most ducks feed intensively on the breeding area. Food needs of breeding waterfowl also vary within species by sex and female body condition (e.g., renesting mallard [Anas platyrhynchos] hens) (Krapu 1981). The diets of 'Present address: Delta Waterfowl Research Station, Rural Route 1, Portage la Prairie, Manitoba R1N 3A1, Canada. This content downloaded from 207.46.13.131 on Sat, 15 Oct 2016 04:19:25 UTC All use subject to http://about.jstor.org/terms J. Wildl. Manage. 49(3):1985 RING-NECKED DUCK FEEDING * Hohman 547 breeding female ducks change seasonally, reflecting changing protein demands. Invertebrates, which are digestible sources of protein with high caloric densities (Reinecke 1977), predominate in female diets during gonadal recrudescence and ovulation (Krapu 1974, Swanson et al. 1974b, Serie and Swanson 1976, Drobney and Fredrickson 1979, Reinecke and Owen 1980, Noyes 1983). Their availability to females may be a major determinant of clutch size (Krapu and Swanson 1975) and laying date (Krapu 1974). Ring-necked ducks are small-bodied (500-900 g), inland diving ducks, which have been studied principally in the Northeast (Mendall 1958). They commonly nest in northern bog-marshes, wetlands of low primary production (Reader 1978, Richardson 1979) that are little used by other ducks. This work was undertaken as part of a study examining energetics of breeding ring-necked ducks. The objectives were to: (1) examine adult ring-necked duck diets in relation to sex and stage of reproduction, and juvenile food habits by age; (2) assess preferences among foods; and (3) estimate rate of food consumption. This paper represents a portion of my Ph.D. thesis work supervised by M. W. Weller and submitted to the Univ. of Minnesota at St. Paul. I was also advised by E. F. Cook, J. A. Cooper, F. McKinney, and J. R. Tester. L. J. Korschgen assisted with seed identifications. R. D. Crawford, R. T. Eberhardt, L. G. Sugden, and M. W. Weller commented on drafts of the manuscript. This is Journal Paper 13838 of the Minn. Agric. Exp. Stn., St. Paul. Financial support was provided by the North Am. Wildl. Found. through the Delta Waterfowl Res. Stn., Minn. Dep. of Nat. Resour., Univ. of Minnesota, Dep. of Fish. and Wildl., Computing Cent., Agric. Exp. Stn., and Graduate School, and the Minn. Waterfowl Assoc.