Among white-tailed deer in Pennsylvania, the rut takes a differential toll on bucks and does. Bucks are on call 24/7 from October through January. Does, on the other hand, are fertile only 24 hours every 28 days. If does are not impregnated during that time, they will come into estrus again in about four weeks.

When not in estrus, does live in small family groups consisting of an adult female and her female yearlings and fawns. As the matriarch's estrus period approaches, she undergoes hormonal changes that bucks can detect in her urine. Bucks use this scent as a cue for when does become approachable.

In September, before the rut actually begins, bucks court does by following them. At this time, females do not permit bucks to approach closely. Usually a buck stays 50 yards or more behind a doe before she enters estrus. He monitors her condition and approachability by sniffing her urine.

If more than one buck trails a particular doe, they will spar until one establishes dominance. That buck will follow the doe until she comes into estrus.

In the days before estrus, a doe's urine scent changes to indicate that she will soon be approachable. When the 24-hour estrus window opens, the buck approaches more boldly and stays at the doe's side until she willingly accepts the buck's advances. At this point a buck and doe can be considered a mated pair.

A buck usually tends a doe for the entire estrus period to prevent other bucks from mating with her. He eats with her, beds down with her for a few hours, and periodically tests her willingness to mate by nosing her rump.

DNA tests show that a buck's vigilance is not always perfect. Occasionally fawns from a doe having twins or triplets have DNA from more than one male.

If a doe does not become pregnant during her first estrus, she gets a reprieve for about 28 days. At that point she once again comes into heat and becomes the subject of intense attention from bucks. Until a doe gets pregnant, estrus cycles continue into February, giving each female multiple opportunities to mate. Consequently, 91 percent of adult does in Pennsylvania ultimately get pregnant.

Next week: In a buck's world.

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