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.