Do Clethrionomys rutilus Females Suppress Maturation of Juvenile Females?

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Abstract
(1) If adult Clethrionomys females suppress the sexual maturation of juvenile females, removing adult females should allow juveniles to breed. We remove all adult Cleithrionomys rutilus females on two areas of white spruce forest in the southern Yukon [Canada] from June to August 1984 to test this hypothesis. (2) More juvenile females become sexually mature on the female removal areas. No juvenile females had litters on the control area whereas thirteen juveniles became pregnant and had litters on the female removal areas. (3) The estimated number of litters on the experimental grids was only 53% that of the controls, so juvenile maturation did not completely compensate for adult female removals. But the number of juveniles caught in live traps on the experimental areas was 88% that of the controls. (4) Survival of males and juveniles was no different on control and experimental areas. We infer that adult female Clethrionomys cause a 30-48% loss of nestlings and post-weanling juveniles before they are caught in live traps. (5) Although there is social control of juvenile maturation by C. rutilus females, this mechanism operates only at high density and cannot explain population fluctuations of C. ritulus in the southern Yukon. We have recorded two outbreaks of C. rutilus 11 years apart, associated with the decline phase of the snowshoe hare cycle and possibly caused by changes in winter food supplies or winter predation pressure.

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