| Summary: | During winter, flocks of Canada geese (Branta canadensis) are common near the rivers that flow through Kamloops. At night, birds gather on the rivers, but during the day they fly into the fields and parks close to the river to feed. As the geese forage, they form groups or flocks of different sizes. This presentation examines some of the hypotheses that have been developed to explain the differences in the size of these flocks. One common hypothesis to explain different group sizes in animals is called the “Many Eyes” hypothesis. It suggests that in larger groups, individuals need to spend less time looking for predators and therefore can spend more time feeding. To test this hypothesis in Canada geese, we videotaped flocks at four locations: MacArthur Island, Riverside Park, Charles Anderson Park, and the Mount Paul golf course. Two-minute segments of these tapes were analyzed by counting the number of seconds each individual of the flock spent either alert, briefly scanning for predators, feeding, resting, or being aggressive. Our results show that as flock size increases, the per capita time that birds spend in alert or scanning behaviour decreases as expected. Also, as expected, the per capita time forging increases. However, for some intermediate flock sizes the per capita forging time goes down and the per capita vigilance increases again. The reasons for such reversals in vigilance and foraging in larger flocks are discussed.
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