The opposite behavior to herding is shown by many female ungulates when they
give birth. At that time they leave the herd and become solitary. This is seen in impala
and other antelopes in Africa, and cervids, mountain sheep, and forest caribou in
North America (Bergerud and Page 1987). This behavior relies on predators spend-
ing most of their search time in areas of high prey density, so that solitary prey at
low density experience a partial refuge and hence lower predation rates.
Another form of refuge is used by deer in winter when they congregate in loose
groups in the small areas between wolf home ranges (Rogers et al. 1980; Nelson
and Mech 1981). These areas appear to be unused by the wolves, a sort of “no-
man’s-land,” and hence they act as a refuge for the prey.Some prey species synchronize their reproduction to lower predation rate on their
young, a behavior called predator swamping. This synchrony is over and above that
imposed by the seasons. For example, moose and caribou have highly synchronized
birth periods (Leader-Williams 1988), as do many ungulates in Africa (Sinclair et al.
2000). Other examples of breeding synchrony are seen in lesser snow geese (Findlay
and Cooke 1982) and colonial seabirds (Gochfeld 1980).
Experimental studies, such as that of foxes feeding in breeding colonies of black-
headed gulls (Larus ridibundus) in England, have shown that those gulls breeding
outside the main nesting period are more likely to lose their nests to predators (Patterson
1965). However, synchrony may or may not be adaptive depending on the abilities
of the predator and the type of synchrony (Ims et al. 1988). Thus, if prey form groups
and all groups are synchronized together, then predator swamping can occur.
However, if reproduction is synchronized within groups but not between them, then
predation rate on juveniles could be increased rather than decreased by this beha-
vior, and this depends on the type of predator (Ims 1990). In general, breeding syn-
chrony should be evaluated not just in terms of predation. Other aspects such as
seasonality of the environment should be considered. These aspects are important
for conservation because species that rely on grouping behavior and synchrony of
breeding will be vulnerable to excessive predation if human disturbances alter either
aspect.PREDATION 177
50403020100
0 100 200 300 400
Wolf density (sightings/1000 hours)Group size (number / group)Fig. 10.11Muskox
group size on arctic
islands in Northwest
Territories, Canada, is
related to wolf density
in both summer ()
and winter (). (After
Heard 1992.)
10.8.3Birth
synchrony