Gulls Are Attracted to Their Predators

When a weasel, fox, or other predator enters a breeding colony of gulls, numerous birds gather in the air above the intruder, making it very conspicuous. Gulls come from a considerable distance and circle or hover over the predator for quite a while, sometimes even landing in its vicinity before returning to their territories. With the exception of those whose nests are immediately threatened, the gulls show little inclination to attack. Instead they appear nervous and ready to flee.

Experiments using models of predators show that breeding Herring and Lesser Black-backed Gulls are more attracted to models that have a dead gull placed close to them than they are to the models alone. Furthermore, once gulls have seen a predator model with a dead gull, they are more attracted to it if experimenters place it within the colony again on the same day, even without the dead gull. Indeed, there is some evidence that the heightened reaction to the predator lasts at least a day after it is seen with the dead bird. This heightened reaction is specific to the predator model seen with the corpse -- there is no increased reaction to a model of a different predator subsequently presented in the same place. After seeing a predator model with a dead gull, the live gulls alight farther from the model on subsequent encounters. They remain attracted, but are more cautious.

These results indicate that the attraction of the gulls to their enemies is a method of learning about them. Apparently they can generalize -- they draw conclusions about the predator after another gull has had a lethal encounter with it. This is a beneficial reaction, since mammalian predators such as weasels and foxes may engage in "surplus killing -- dispatching more victims than they can consume. Also these hunters can specialize for a period of time on one group of prey. An animal that has killed one gull may be more likely to kill others; individual foxes have been observed habitually killing gulls in breeding colonies. It requires little imagination, then, to see the potential adaptive advantage for gulls of investigating predators.

SEE: Natural Selection; Flock Defense; Coloniality; Distraction Displays.

Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.