Reproductive tactics of pikas: why have two litters?
Abstract
Reproduction in a population of marked pikas (Ochotonaprinceps) was observed over a 3-year period in the Rocky Mountains of Colorado. Pikas were seasonally polyestrous; all adult females initiated two litters each summer. However, most females (24 of 25) weaned only a single litter. The number of successfully weaned litters and offspring was divided evenly between first and second breeding attempts. Previous studies had noted that less than 10% of juveniles emerged from second litters. Apparently females are capable of weaning second litters, but only if first litters are lost. Loss of first litters may result from nest predation or poor maternal condition caused by extreme winters. Reproductive constraints acting on pikas and their evolved reproductive tactics are compared with those of other alpine or boreal long-lived herbivorous small mammals.
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