POPULATION CYCLES IN SMALL MAMMALS
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J A S O N D J F
MONTH
Fro. 37. As the population of Microtua d$n-nkua decreased from the peak of
214 200 voles in the 2380 acres of suitable habitat on Grizzly Island, the percentage of the vole population which wm taken m h month by the whitetailed kite, short-eared owl and the barn owl increased. Data from Stendell
(unpublished).
predation was working (Table XVII). For 11 months (September to
July) no Microtw were trapped but scats deposited on the study area
still contained Microtw remains. This shows that terrestrial predators,
in this case primarily feral cats, were able t o find Microtus even when
their numbers were low and their distribution patchy. What we need
to know is whether predation pressure is strong enough to prevent
the build-up of Microtw populations when they are at low numbers.
For the present it must be concluded that feral cats are more persistent
at searching for Microtw when they are at low numbers than are
students of small mammal populations. These observations are consistent with Pearson's hypothesis.