Group Foraging
Bluegill sunfish obtain food by flushing (forcing into the open)small aquatic insects from dense vegetation. Researcher Gary Mittelbach hypothesized that larger foraging (food searching)groups might flush out more prey and increase the average number of prey obtained per group member. He examined this hypothesis by experimentally manipulating the foraging group size of bluegill sunfish in a controlled laboratory setting. Mittelbach placed 300 small aquatic prey into a large aquarium containing juvenile bluegill sunfish. He examined the success of bluegills that were foraging alone, in pairs,and in groups (ranging from three to six bluegills). Mittelbach measured the number of prey captured per bluegill, and he found a positive relationship between foraging group size and individual foraging success (the larger the group, the greater the success) up to a group size of four fish.The increased feeding rate per individual was due to two factors.First, more prey were flushed when group size rose.Second, prey clumped together, so when one group member found prey, others swam over to this area and then often found food themselves.
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