Wildlife: Early breeding makes life easier for some animals

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In nature, timing is everything. Most animals give birth in the spring just as new food sources become abundant. But for many species, the mating season begins much sooner.

The white-tailed deer rut, for example, peaks in late fall. Does are fertile for only 24 hours every 28 days. Bad weather or too much human activity can disrupt deer activity, so unmated does can extend the mating season into early February. Deer pregnancies average 200 days. Fall mating is essential to ensure that fawns drop with sufficient time to mature by the following autumn.

Black bears breed in June and early July, when food is abundant. Though embryos form in early summer, they do not implant on the uterine wall until the sow enters hibernation. This enables sows to acquire vast amounts of fat even while pregnant. Even after fetal development begins, it proceeds slowly with minimal stress on the mother. Black bear cubs weigh just 6 to 12 ounces at birth in January. Most bear cub growth occurs after birth.

Several members of the weasel family take this strategy of "delayed implantation" to extremes. Fishers, river otters and long-tailed and short-tailed weasels mate in March or April, but don't give birth until about 10 months later. When the embryos finally implant in late winter, the actual pregnancy lasts only four to six weeks. This ensures plenty of prey for nursing mothers and for the young when they leave the den.

Even trout respond to fall's seasonal cues. Females transform into egg-making machines. Female brook trout choose clean, gravelly spawning sites when the water temperature is between 40 and 55 degrees. And there must be an upwelling of ground water directly beneath the nest, or at least a current, to carry away silt and sediments.

When the female trout releases her eggs, the male fertilizes them. The spawn is complete. The fertilized eggs settle into the gravel, safe and ready for a winter of dormancy. The eggs hatch in early March.

Brown trout follow a similar fall spawning pattern when water temperatures dip into the upper 40s.

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


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