January 01, 2019We normally assume that all sexually mature whitetail bucks compete aggressively to breed as many does as possible. But is there any evidence that some "big" bucks, otherwise physically and physiologically normal, opt not to compete for breeding privileges?
Until reading Valerius Geist's account (in the 1994 Stackpole book, Deer) that some big mule deer bucks choose not to partake in the frenzy of the rut, I admittedly had never really pondered the question.
Geist suggests that such "nonparticipants" are generally very large bucks with huge antlers. Also, they do not socialize with other large bucks, therefore presumably are not part of the structured male society, and tend to stick to very heavy cover.
At least one of the bucks Geist had studied was a middle-age animal that had behaved normally until the "old master buck" thoroughly trounced him in battle. The vanquished buck then did not rut for several years thereafter. Later, however, after the population declined, and virtually all large bucks had died, this particular buck became the alpha buck, a status he held for three consecutive years.
In Geist's view, "The opting-out strategy works when there is a die-off, as can happen in a severe winter. When the large bucks, exhausted by the rut, may die, he is more likely to survive, having spent the fall feeding and resting. Not only does opting out preserve the buck's fat reserves, which he may then draw on to survive lean times, but it also gives him a head start for growth the following spring and summer.
"This in turn increases his chances for survival and his ultimate body size and thus his ability to fight during the next rut. Moreover, following a population crash and the concomitant decline in sexual competition, a huge master buck may now breed a greater number of females. That buck thereby increases his genes disproportionately in the herd."
Kenny Darwin photo
Looking back at over 20 years of data from my Cusino deer enclosure studies, I know of one whitetail buck that also used the "opting-out strategy" successfully. Although I seldom observed this particular buck (M-5), he did not associate with the other bucks and apparently did not compete for breeding rights. He too grew to be very large, but held a low dominance rank when we live-trapped him annually and placed him in a holding pen with the rest of the herd.
Most interestingly, what we examined M-5's blood, we found that he had unusually high plasma progesterone values (typically regarded as a female hormone, but produced in quantity by the adrenal gland when animals are stressed). However, when the alpha buck was poached, M-5 immediately assumed the top position on the dominance hierarchy, and his progesterone values dropped to a normal level. He held his alpha rank for the next three years before he was removed from the population.
Geist observes, however, that the opting-out strategy doesn't always payoff. The largest buck he studied, for example, also chose not to participate in the rut, but died before a population decline and probably never did breed.
Granted, whitetail bucks probably only opt out of the rut when populations are high, and only when other mature bucks are present. They probably aren't very common either. But maybe this behavior explains why, every now and then, some monster buck just seems to materialize out of nowhere.
I know, for example, that one buck fawn I released from the Cusino square-mile deer enclosure was not harvested by a hunter until it was 10.5 years old, despite residing in the immediate area for all those years.