Search-Path Characteristics of Foraging Ruddy Ducks

Abstract

I analyzed the search behavior of 6 Ruddy Ducks (Oxyura jamaicensis) foraging on patchily distributed prey in a large aquarium. When searching for randomly placed food patches, Ruddy Ducks sampled previously profitable sites before investigating other areas more frequently than would be expected by chance. Revisiting previously profitable foraging sites may be important when exploiting a patchy food resource with prey densities that are likely to be quickly replenished after having been exploited. I also analyzed search paths of birds before and after they encountered prey and in low- (50 prey) and high- (250 prey) density patches. Search paths in food patches were longer in length and duration, had a lower velocity, and were more sinuous than in areas devoid of food. These search-path characteristics enable predators to locate and exploit patchily distributed food more efficiently than random search. Search-path length was similar in low- and high-density patches, but search-path duration was shorter in low-density patches in 5 of 6 birds. Search-path velocity was faster in low-density patches in 4 of 6 birds. Search-path sinuosity did not differ between low- and high-density patches. The differences in search-path characteristics between patches with different prey densities may be related to handling time of the food items.