Mice and Ground-nesting Birds

photograph of a Spotted Sandpiper by Rohan Kamath
Classically rats, ground squirrels, foxes, coyotes, and other mammals have been recognized as important predators of the eggs of birds that nest on the ground. And mice long have been suspected to be major destroyers of tern eggs. Now, there is substantial evidence that these small rodents may have a significant impact on the reproductive success of shorebirds. During an intensive study of a Spotted Sandpiper population nesting on an island in a Minnesota lake, two ornithologists, Stephen Maxson and Lewis Oring, noticed that many nests contained fewer eggs than the usual clutch of four. They discovered that this was due, at least in part, to overnight damage to a single egg in the clutch, and (often) the subsequent disposal of that egg by the adult birds. Usually the damaged egg had two punctures, about as far apart as mouse incisors, and mouse droppings were often found near the nests; on several
occasions, incubating sandpipers were seen chasing mice that approached their nest during the daytime. Oddly, the mice did not eat the damaged eggs, although sometimes albumin leaked from them and presumably was consumed. If the albumin was not eaten, the behavior of the mice is more difficult to understand. Also the failure of the birds to defend their eggs better at night remains to be explained. Over a three-year period, between 6 and 34 percent of the sandpiper eggs failed to hatch because of mouse damage.

Outside of the arctic and (in one report) temperate grasslands, this is the first documented evidence of small rodents like mice as enemies of birds. Since the two species of mice incriminated in the destruction of Spotted Sandpiper eggs are widespread and common in North America, mouse predation on eggs, and perhaps young, of ground-nesting birds may be more important than has been thought previously.
SEE: Empty Shells; Polyandry in the Spotted Sandpiper; Sandpipers, Social Systems, and Territoriality; The Decline of Eastern Songbirds; Gulls Are Attracted to Their Predators.
Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.