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PrintThe breeding season of white-tailed deer in Pennsylvania, commonly called the rut, begins in October and extends into February. Though bucks gather in small social groups during most of the year, in September a clear dominance hierarchy develops.
Larger, older bucks, especially those with larger antlers, dominate smaller, younger ones. Smaller bucks avoid larger ones to conserve energy and avoid injuries that might occur during a fight. A 98-pound weakling knows better than to challenge a macho buck.
Most Pennsylvania hunters know that most deer hunting takes place during the mating season, also known as the rut. Fewer, however, understand the timing of white-tailed deer reproduction. According to surveys and analysis by Game Commission biologists:
• The rut peaks on Nov. 14.
• Among 2-year old does, 34 percent carried a single embryo, 64 percent carried twins and 3 percent carried triplets.
• 90 percent of adult does breed between Oct. 27 and Dec. 10.
• 91 percent were pregnant.
• The rut peaks on Dec. 2.
• 26 percent of were pregnant and of those, 83 percent carried a single embryo, 16 percent carried twins and less than 1 percent carried triplets.
• Mature females usually carry twins.
• Bucks prefer to mate with mature females.
When confrontations occur between near equals, the response of dominant and subordinate bucks is predictable. The lowest form of confrontation is a direct stare. Subordinate bucks simply look away and back off. In a more aggressive encounter, the dominant buck will hold its head high or low. A low-head posture indicates the dominant buck is ready to chase, while a high head posture indicates a dominant buck is ready to rear and fight.
Encounters such as these occur soon after bucks lose their antler velvet, so in September bucks spend a lot of time posturing to establish dominance. During this period, bucks often spar in what seem to be simple pushing contests. Bigger bucks almost always win these head-to-head shoving matches. The vast majority of physical encounters are ritualistic and safely resolved.
As does come into heat in October, bucks become more solitary and turn their attention to the opposite sex. A doe's estrus cycle lasts only 24 hours, so a courting buck becomes preoccupied with a single doe. He stays by her side until she accepts his advances. This explains why hunters often observe a big buck following a group of does.
A buck's preoccupation with a doe in heat takes him out of the competition for other does. This is how subordinate bucks are able to gain access to does in heat.
After mating, the rut continues for healthy males. It's an exhausting three or four months. During that time, a buck can lose 25 percent of its body weight.
Complicating white-tail breeding biology is the fact that does in a specific geographical area come into heat at approximately the same time. So, over the course of just a few days, most of the does in an area will be available for just 24 hours. This also helps insure that more than just a few dominant bucks get to breed.
Does that do not become pregnant during their first estrus will recycle in 28 days. This is why the rut lasts as long as four months. In Pennsylvania, 90 percent of adult does become pregnant by mid-December.
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