Predatory efficiency and energetics of belted kingfishers wintering along the Mad River

Belted kingfishers (Ceryle alcyon) were studied for two winters along the lower fad River, Humboldt County, California. Kingfishers spent 79.6 percent of daylight hours hunting, 12.2 percent inactively perched, 4.0 percent on intraspecific interactions, 2.3 percent handling prey, 1.6 percent preening and bathing, 0.18 percent in interspecific interactions, and 0.1 percent flying in response to human disturbances. Kingfishers spent 11 percent more time hunting during the winter of 1975-76 than during the less severe winter of 1976-77. Fish comprised 91 percent of the prey identified; salmonids (Salmonidae), sculpins (Cottidae), and sticklebacks (Gasterosteidae) were the three major types of fish taken. Time spent subduing fish and the number of beats delivered to fish were positively correlated with length of fish. More time and a greater number of beats were needed to subdue sticklebacks and sculpins than salmonids of the same size class, possibly because more effort was required to disable the protective spines of sticklebacks and sculpins. Over 50 percent of strikes from perches resulted in captures of prey, while only 20 percent of strikes from a hovering position were successful. Strike success was negatively correlated with the disturb-ance of the water's surface and was lowest when almost dark, highest at dusk, and decreased as light levels increased. On the basis of 19 complete days of field data, kingfishers were observed to consume a mean of 70.2 kcal per day while an energetics model developed by Koplin et al. (1980) predicted 72.3 kcal would be required daily assuming an assimilation efficiency of 0.821. From this model the population of 25 kingfishers wintering on the lower Mad River was predicted to have required 337,925 kcal or 84,481 fish of 4 g each, during an average winter.