Hunting animals, such as deer, is often important to keep their population at a reasonable size. In areas where natural predators are few or non-existent, the only way to control populations of certain species is through human hunting.
However, human hunters behave differently from natural predators. For example, natural predators aren’t interested in trophy hunting, so they don’t target animals that would look good on their walls. Natural predators are also not reluctant to kill the young, while human hunters usually avoid doing so. And human hunters can make different decisions about what to kill based on factors we don’t really understand.
To understand how these factors may affect prey populations, a group of researchers in Norway, Germany and the Netherlands published a paper attempting to predict hunter behavior.
The idiosyncrasies of human hunting create distinctive evolutionary pressures. Populations of animals hunted by humans differ from those hunted by natural predators. Features prized as trophies (such as large antlers) are rapidly disappearing from the population. And the population is allowed to grow, precisely because mothers with young are often left alone.
So while hunting can play a role in maintaining ecosystems, we need to understand how human hunters behave. This makes it possible to predict their choices and how those choices will change the population of hunted animals. This, in turn, makes it possible to steer conservation policies to ensure the sustainability of the hunted population.
The researchers assume a hypothetical situation in which a hunter is confronted by a deer and must choose whether to shoot that deer or wait for another. Many factors play a role in that decision. Naturally, the hunter’s perception of the quality of the animal plays a role. Where deer sightings are rare and the hunter knows they may not see another, they may be more inclined to shoot for sure rather than wait for a better quality animal. Depending on the region, there may be other restrictions such as quotas, time remaining in the hunting season, and competitive pressure from other hunters.
The researchers treat all of these factors as an economic problem and put them into equations that predict how a fighter will react to different situations. The model predicts that the more competition from other hunters, the fewer days left in the season, and the less likely you are to see an animal, all increase the likelihood that a hunter will fire rather than wait.
So far this is consistent with common sense, but it is also completely hypothetical. People often happily march in a different direction than what models predict, so it’s important to compare the predictions with real-world data. Fortunately, hunters in Norway are required by law to report how many hunters went out in a group, how long they hunted, how many deer they saw, and how much they shot. Collecting this data from 256 locations over 10 years provided a solid data set for field testing.
The researchers used this data to calculate the probability of a male deer being shot by a hunter in different scenarios. As predicted by the theoretical model, the chance was higher when competition with other hunters was a problem, when there were few days in the season, and when there was a lower chance of seeing a deer at all.
This recent work does not address all questions of individual choice. This study looks at Norway, but pressures can vary widely in other locations. For example, a region may have no quotas (unlike Norway), or a region may be full of hunters who are pressured to bring food home from a hunt. Hunters who come from different social groups also behave differently: This data showed a difference between weekend and weekday behavior, suggesting that local hunters who hunt during the week behave differently than non-residents who come on weekends. By finding out how different social groups behave, policymakers can make more accurate predictions.
Currently, models are used to estimate how hunting will affect the size of a population. Population size is an important factor for conservation policy makers, but “there is increasing concern that hunting, and in particular highly selective hunting, may have unexpected ecological and evolutionary consequences,” the researchers write.
An analysis like this could help to address the problem of high selectivity among hunters. For example, by changing the length of the hunting season or the number of competing hunters, the selectivity of the hunters can be influenced. Just looking at the number of animals shot is not enough to inform conservation, the researchers write: “To achieve sustainability, future wildlife management must account for the predictable ways in which social constraints and underlying intuitions shape the emerging pattern of selection.”
PNAS2016. DOI: 10.1073/pnas.1607685113 (About DOIs).