Niche Overlap and Habitat Use by Sympatric Duck Broods in Eastern Washington

Abstract

We evaluated niche overlap and habitat use among duck broods on Turnbull National Wildlife Refuge (Turnbull NWR). During summer of 1983 and 1984, 485 observations were recorded in 46 days. Data were gathered on 320 feeding broods of 9 species along 12 niche dimensions. Mean niche overlap values ranged from 0.62 to 0.94 for 36 possible species pairs. The greatest niche separation occurred on hatching date and feeding depth dimensions. Gadwall (Anas strepera) and teal (A. discors and A. cyanoptera) broods were ecologically very similar. Both had sharp mid-season hatching peaks and fed over dense beds of submerged macrophytes. Five species of diving duck broods tended to feed in deeper water and over areas with sparse submerged macrophytes. Among diving ducks, bufflehead (Bucephala albeola) broods were ecologically distinct, feeding over sparse vegetation often far from land. Mallard (A. platyrhynchos) broods were ecologically isolated from other dabbling ducks. They fed in shallow water within stands of emergent vegetation. The niche for ring-necked duck (Aythya collaris) broods was most similar to dabbling ducks, but also showed similarities with other divers. J. WILDL. MANAGE. 52(1):95-103 Studies dealing with brood-rearing ecology often emphasize macrohabitat (Stoudt 1971, Mack and Flake 1980, Swanson et al. 1984). Multi-dimensional studies of niche and niche overlap by sympatric duck broods are lacking. However, several studies have reported temporal segregation for both adult ducks and broods. Nilsson (1970) observed species of diving ducks segregating their feeding activities by diurnal and nocturnal partitioning. Morning and evening feeding peaks have been documented for broods of various species (Hochbaum 1944, Chura 1963, Ringelman and Flake 1980). Ringelman and Flake (1980) reported some temporal differences in feeding activity between blue-winged teal and mallards in age classes I and II. Differences in hatching dates among sympatric duck species are well documented (Hochbaum 1944, Hines 1977, Toft et al. 1984). Koskimies and Lahti (1964) reported differences in low temperature tolerances for several species of ducklings. Dietary overlap has been reported for sympatric species of ducklings, especially neonates (Collias and Collias 1963, Bengtson 1971, Sugden 1973). Among older ducklings, overlap is reduced as species become morphologically (Nudds and Bowlby 1984, Nudds and Kaminski 1984) and behaviorally specialized (Collias and Collias 1963, Sugden 1973). Sugden (1973) suggested dietary overlap in ducklings may not represent competition because substantial overlap occurred only among very young broods. Collias and Collias (1963) reported that ducklings of different species tended to specialize on different invertebrates. Our study examined microhabitat use by duck broods. Our objectives were to describe quantitatively species-specific use for several spatial and temporal niche dimensions and measure niche overlap between and among species for these dimensions. We use the term brood to refer to ducklings within a accompanied by an adult hen. Thus, when we refer to habitat use we recognize that in some cases the brood-rearing hen may have selected the site. Our study was funded by the Turnbull Laboratory for Ecological Studies, Eastern Washi gton University. We are grateful to refuge personnel for their cooperation and use of equipment. Appreciation is extended to R. L. Carr and R. A. Soltero for advice and encouragement. We acknowledge J. R. Rees, R. B. Pharness, and J. R. Alldredge for their helpful suggestions. We thank D. C. Douglas, P. J. DuBowy, R. M. Kaminski, J. A. Mueth, L. W. Ratti, K. P. Reese, J. K. Ringelman, J. J. Rotella, M. W. Weller, and L. G. Sugden for careful review of the manuscript.