Reproduction
Reproduction in Blarina brevicauda occurs during the breeding season, which lasts from early February until September . There are two peaks of breeding, the first in spring and the second in late summer to early autumn .
During the reproductive period, female shrews tend to increase in size as well as appetite and will diversify their food sources and venture further to gain nutrients (Getz et al. 2008). Because of their high resting metabolic rate, the shrews reproduce frequently with upwards of 20 or more matings occurring in a single day . The repetitive copulation is needed in order to induce ovulation, as a minimum of six matings is required . Copulation in the short-tailed shrew can last as long as 25 minutes with the average length being 5 minutes . The female directs the copulation, positioning herself accordingly while the male is asleep . The female strengthens the nest when the young are nursing, and is more active to support her increased nutritional needs. The young, which were born hairless and blind, weighing less than a gram, may become sexually mature in as soon as two to three months. Those born in the spring mature more quickly than those born late in the season, and may themselves reproduce in the same year they were born. The juvenile pelage is pale and quite similar to the adults' summer fur, and is molted when the young reaches adult size.B. brevicauda is promiscuous. Male shrews in captivity were observed to make clicking sounds while courting a female..
Once pregnancy has occurred, the gestation period is 21 to 22 days on average, with litters approaching a mean number of 6 or 7 young . The weaning of the young occurs by 25 days old . Most B. brevicauda do not live beyond a year and in the case of the death of the litter, estrous in the mother will reoccur . The number of offspring in a population per year varies on a random basis leading to fluctuations in numbers but as the species is a generalist as are its predators, the impact of these random changes is not significant .
Read more about this topic: Northern Short-tailed Shrew
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