An approach to assess stress in response to drive hunts using cortisol levels of wild boar (Sus scrofa)

Justine Güldenpfennig,Oliver Keuling,Ursula Siebert,Martina Hoedemaker,Marion Schmicke

doi:10.1038/s41598-021-95927-2

Abstract

Hunting can easily be linked to stress in wildlife. Drive hunts performed two to three times in one area during the respective hunting period, are thought to decrease the pressure hunting places on wildlife. Nevertheless, the expression of cortisol—one of the main mammalian stress hormones—is considered to have negative impacts on animals’ well-being if expressed excessively, which may occur during some (especially repeated) hunting events. We explored the effect of drive hunts on cortisol levels in wild boar in Lower Saxony, Germany, compared these cortisol levels to reference values given by a similar study, and investigated the effect of age, sex, and pregnancy. Blood collected from wild boar shot on drive hunts was analysed using a radioimmunoassay. As expected, we observed elevated cortisol levels in all samples, however, we still found significant differences between age groups and sexes, as well as an influence of pregnancy on cortisol levels. The effect of drive hunts on cortisol levels appears to be weaker than predicted, while the effects of other variables, such as sex, are distinct. Only half of the evaluated samples showed explicitly increased cortisol levels and no significant differences were found between sampling months and locations. Group living animals and pregnant females showed significantly higher cortisol levels. The impact of hunting is measurable but is masked by natural effects such as pregnancy. Thus, we need more information on stress levels in game species.

Highlights

Hunting can be linked to stress in wildlife
We investigated the following questions: (1) What are the stress levels of wild boar during drive hunts, (2) can we ascertain elevated cortisol levels caused by stressors such as repeated drive hunts using values given in a similar s tudy[21], and (3) are there differences between age groups and sexes, as well as pregnant and non-pregnant wild boar? Pregnancy, as another factor possible to influence cortisol levels[37,38], should be taken into account to exclude its effect on possible differences between the stress response of male and female wild boar
Given the fact that we sampled after drive hunts, our results show a high percentage of trauma cortisol levels (54%)

Summary

Introduction

Hunting can be linked to stress in wildlife. Drive hunts performed two to three times in one area during the respective hunting period, are thought to decrease the pressure hunting places on wildlife. The negative effects on the well-being, stress and high cortisol levels are most likely to influence the relationship between wildlife and disease as well as host-parasite equilibrium, which can influence animal populations and lead to loss of biodiversity[7]. A few studies about cortisol in wild boar are available, which show differences in sampling method (e.g. sampling from living animals with t rapping[20] or from dead animals after hunting and other t rauma21) and other limitations[20]. Gentsch et al defined “normal” (shot on single hunts, no previous disturbance) and “trauma” (shot on driven hunts with previous disturbance, death due to accidents) cortisol levels of wild boar and other ungulate species in response to different hunting methods[21]. Knowledge of wild boar stress and stressors may help to improve domestic pigs’ welfare in pig farming, by supplementing the available stress research specific to domestic pigs

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Results

Conclusion