Foraging behaviour of American oystercatchers in response to declining prey densities

American oystercatchers (Haematopus palliatus) responded to declines in the density of oysters (Crassostrea virginica) on a commercial oyster bed examined in 1979 and 1995 by increasing the number of species of prey eaten and search times, but not peck rates or handling times. Seasonal changes in foraging behaviour included oystercatchers choosing larger oysters with longer handling times in winter than in autumn, but with subsequently greater profitability and higher intake rates. Time budgets of foraging birds were similar in the two seasons. Oystercatchers ate fewer mussels in winter than in autumn, and fewer mussels than oysters at all times. Search and handling times for mussels were similar in autumn of the 2 years. After a commercial harvest of oysters at a second site, handling times for oysters did not decline; however, search times were significantly more variable, niche breadth was greater, and there was a trend towards longer search times post harvest. The recorded changes in foraging behaviour indicated a close match between search and handling times and prey density and size and behavioural flexibility of foraging birds in response to sometimes drastic changes in their prey base.