Aggression and habitat segregation among diving ducks wintering in South Carolina
Bergan, James F
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Aggression and habitat segregation among buffleheads (Bucephala albeola), lesser scaup (Aythya affinis), ring-necked ducks (Aythya collaris), and ruddy ducks (Oxyura jamaicensis) were investigated in 1985 and 1986, on Par Pond, South Carolina. A total of 4,567 focal individuals were sampled during 384 hours with nearly equal representation of species and sexes. Intraspecific aggression was infrequent (N=69). Interspecific aggression accounted for 228 observations which included American coots (Fulica americana) and pied-billed grebes (Podilymbus podiceps). The ring-necked duck was most aggressive (^=62 intra- and interspecific encounters). Time spent in aggressive activity was less than 1% for all species. Habitat availability - use analysis determined that both inter- and intraspecific habitat segregation occurred over 4 habitat types. Segregation, in the absence of an appreciable amount of aggression, suggests that the inter- and intraspecific dominance hierarchies, as reported among other wintering waterfowl assemblages, do not exist among species in this study. Time-activity analysis indicated that foraging was the most important activity for all species. Buffleheads foraged more than any of the other species. Courtship behavior was exhibited often by buffleheads, and more infrequently by ring-necks. Among lesser scaup and ring-necked ducks females spent more time foraging and less time resting/sleeping than did males. Time spent foraging by buffleheads, lesser scaup, and ring-necked ducks increased throughout the winter. The aforementioned diurnal activity trends were also detected during nocturnal hours. However, foraging time was lower for all species except ruddy ducks, which actively fed at night. Diel feeding activity peaks varied by species but in general, most feeding occurred during the late night (0230 - sunrise), early morning (sunrise - 1030), and midday (1030 - 1430) periods. Behavior investments also varied by location. At the Cold Dam site, time spent in locomotion was highest while feeding time was generally less for each species relative to the other two locations. Variation between diurnal and nocturnal time budgets illustrates the importance of considering the entire 24-hour cycle of wintering waterfowl behavior rhythms. In addition, spatial differences in behavior indicate that variation can occur between sites. Measured weather variables accounted for little variation in behavioral investments.