Wildlife: Late-season mating a good strategy for larger mammals

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It's common knowledge that wildlife breeds in the spring. When it comes to medium and large mammals, however, common knowledge is often wrong.

Mating season peaks in mid-winter for many mammals, and some species actually mate a year in advance of giving birth.

Fishers, a large member of the weasel family, mate in early spring, but the pregnancy lasts almost a full year. After fertilization, the tiny embryos remain in the uterus but do not implant on the uterine wall. After 10 to 11 months, these "blastocysts" finally implant and a functional gestation period of 30 to 60 days follows. Two or three pups are born in March or April.

The "delayed fertilization" characterizes several other members of the weasel family and black bears.

River otters mate in March or April and give birth to two or three pups the following February or March. Embryos do not implant on the uterine wall for up to 10 months, followed by a functional gestation period of about 50 days.

Black bears don't mate until June or early July, and embryos do not implant until females enter hibernation. Two or three cubs are born in January while still in the winter den. Delayed implantation permits females to meet the energetic demands of pregnancy while food is abundant. And young animals leave their dens just as food becomes relatively easy to find.

Beavers and porcupines enter the world fully furred, with teeth erupted and eyes open. They breed in February and 12 weeks later give birth to four or five young. Porcupines have a much slower reproductive rate. After mating some time in October or November, and following a 210-day pregnancy, females give birth to a single porcupette.

Bobcats can breed throughout the year, but most mate in late winter. After a gestation period of 60 days, two to four kittens are born in the spring. And raccoons mate in January or February. After a pregnancy of 63 days, raccoons give birth to three to six pups.

Though hardly a complete review of mammalian reproductive biology, this brief review illustrates the diversity of strategies larger mammals use to get a head start on the mating season.

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Biologist, author and broadcaster Scott Shalaway can be heard 9-11 a.m. Saturdays on 1370 AM WVLY (Wheeling) and noon-2 p.m. Sundays on 1360 AM WMNY (Pittsburgh). He can be reached at http://scottshalaway.googlepages.com, and 2222 Fish Ridge Road, Cameron, WV 26033.


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