Hunting: What is the ideal doe-to-buck ratio for Maine’s deer herd?
By BOB HUMPHREY December 19, 2021
This year’s deer harvest is likely to set records, at least for recent years. The biggest contributing factor was the number of any-deer permits handed out by Maine, which was welcomed by many hunters. Some merely wanted a better chance for success while others have long complained about too many does or a buck-to-doe ratio that is way out of whack. Is it possible to have too many does? Can the ratio get so skewed it’s detrimental to the herd or to hunting? Let’s take a look.
Determining how many deer is too many may not be as simple as it seems. Biologists use the term carrying capacity – how many individuals of a particular species can be supported in a specific area without harm to the habitat or the animals. In the absence of humans, most areas can support far more deer than you might think. With a higher population, die-offs will be larger in more severe winters, but a certain proportion of the herd would die off anyway so you’re left with roughly the same number of deer whether the pre-winter herd was large or small.
It is humans that prompt wildlife managers to try to maintain deer herds at some level below biological carrying capacity. First, there’s hunting. Biologists have determined that holding the herd at somewhere around 70% of biological carrying capacity produces optimum sustained yield, the right balance between herd recruitment and hunter satisfaction. Then there’s negative interactions like car-deer collisions, property and crop depredation, and an increase in Lyme disease. Where those are prevalent, wildlife managers set their population objectives at an even lower level, sometimes referred to as social or cultural carrying capacity. That’s often somewhere in the neighborhood of 50% or less of biological carrying capacity – half as many deer as the habitat can support. That’s the objective in many parts of southern and central Maine yet some hunters still complain there are too many does.
To an extent, the more females the better, as they represent the reproductive potential of the herd. You also want more does than bucks because deer are polygamous and one buck can breed multiple does. It then becomes a matter of balancing the sex ratio. If there are too many does, the bucks may run themselves ragged trying to chase them down during the rut, and some does may no get bred; or so say the detractors.
The skewed sex ratios hunters observe may not be as bad as they think. There are more of them, but antlerless deer also tend to be more viewable than adult bucks. Furthermore, hunters typically consider all the antlerless deer they see to be adult does when in fact, at least half are probably fawns, and half of those are buck fawns. They complain about 10-1 or even 15-1 ratios of does to bucks, but that simply can’t happen in a managed herd.
According to Kip Adams, chief conservation officer for the National Deer Association, the biological maximum is roughly a 5-1 ratio, even in the absence of a doe harvest because a certain number will perish anyway. Adams gives the hypothetical example of a population of 120 adult deer, with an unnaturally skewed ratio of 100 does and 20 bucks (5-1). Hunters kill 90 percent (18) of the bucks and none of the does, leaving 100 does and two bucks, after the season.
Next comes natural mortality. With fewer bucks in the population, fewer will die; we’ll say 50 percent, leaving one buck. At least 10% of the does will die, leaving 90 does and one buck. That seems pretty skewed, but we haven’t yet considered fawns and recruitment.
Average fawn recruitment is about 0.83 fawns per adult doe, with roughly a 50-50 sex ratio. In our example, that gives us 75 more deer: 38 bucks and 37 does. Assuming the same ratio for the previous year, our pre-hunt population now has 127 does and 39 bucks for a 3-1 ratio.
Add any hunting mortality on does and that ratio gets shifted even more in favor of hunters that are seeking bucks.
Time will tell whether this year’s generous prescription of any-deer permits will address perceived problems. The heavy hit does took will certainly impact reproduction and recruitment. Meanwhile, hunters exacted a heavy toll on bucks as well. Deer are resilient creatures and the herd will recover in time, but hunters should expect to see fewer deer around next fall and for those who championed thinning the doe numbers it may be a case of, “Be careful what you wish for.”
