There are many factors dictating when a buck drops its antlers.
QUESTION: It’s March 20, the first day of spring, so why are so many bucks still seen with antlers?
ANSWER: While seasonal changes in deer physiology and behavior are prompted largely by photoperiodism (changes in the amount of daylight), it is not a precise mechanism, and there are always exceptions.
In general, waning day length causes a reduction in production of certain hormones, like testosterone. That, in turn, causes an abscission line to form at the pedicel base as connective tissue dies. Then the antlers fall off.
When this occurs varies with the age and health of the deer, among other things. Older bucks tend to shed earlier. Injured bucks might also cast off their antlers sooner, although that, too, depends on the type of injury. In rare cases, an injury can result in a buck keeping its antlers longer, sometimes indefinitely. Also, like humans, every deer is an individual, and some just shed earlier or later than others. — Recent Ask the Biologist Question:
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