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Age-related Fecundity in Four Taxa of Western Shrews (Sorex spp.).
INTRODUCTION
Litter size declines with age and parity in females of many, but not all, species of polytocous domestic and wild mammals (Sadleir, 1969; Nalbandov, 1976). Some researchers reported that most female shrews of the genus Sorex produced one litter, rarely two, during the breeding season (Clothier, 1955; Rudd, 1955; Johnston and Rudd, 1957), whereas others reported postpartum pregnancies in 12-50% of females examined and speculated that some individuals may have produced three litters (Jameson, 1955; Gashwiler, 1976). By examining repeatedly live-trapped vagrant shrews (Sorex vagrans) Hawes (1975) found 5 (33.3%) of 15 females produced two litters and six (40.0%) produced three litters; litter size could not be determined because of the nature of the study. Despite short periods of gestation and lactation, the short life-span of most Sorex (Churchfield, 1990) probably precludes production of more than three litters by the most fecund females.
Among pregnant western shrews (Sorex), …
