I’ve most often seen the term “compensatory” used when describing the effect of hunting on game bird populations. At first glance, one might assume that the population of game birds at the end of a year which included hunting, might be the total number of birds at the start of the year minus the sum of birds killed by hunters and the birds which died from natural causes. In this case, the number of bird deaths would be additive.
A key to understanding the compensatory concept is the realization that changes in population density impact habitat and bird health. Therefore, when birds are removed from the population early on in a season, the remaining birds benefit from the population decrease. They have fewer birds competing with them for food and therefore are more likely to remain healthy and survive.
Not only that, but with fewer game birds in the population other sources of population depletion may be impacted. For example predator populations may decline. Or, a decrease in population density may prevent the spread of disease that might otherwise occur.
In a perfect world, precisely the right number of game birds are killed by hunters, thereby reducing the population to where a high percentage of the remaining birds survive. When this is the case, the effect of hunting is negligible.
Another case that clearly demonstrates the benefits of using compensatory mortality is when a severe weather event causes a dramatic decrease mule deer habitat and food supplies. By removing deer from a specific herd, the remaining animals in that herd will have a better chance of surviving. If there’s only enough food for a predictable number of deer to live through a tough winter, game managers may call for a special hunt to reduce the population and prevent mass starvation.
Unfortunately other limitations make it difficult to manage precisely.