Bears on the move: effects of human development and climate change on hibernation in a large carnivore

How is climate change affecting both black bear hibernation and our interactions with the species? Associate Editor, Claudia Bieber comments on the recent article, Human development and climate affect hibernation in a large carnivore with implications for human–carnivore conflicts by Heather Johnson et al.

As we were enduring extremely high summer temperatures in Vienna, it was indeed refreshing to find a manuscript dealing with hibernation in my inbox. Besides the welcome thoughts about snow cover and cool temperatures, the study did, however, highlight that we live in a world facing climate change and we are still at the very beginning of understanding its effects on plants, animals and ecosystems. In this context, limited attention is paid to hibernating species. This is especially disappointing since a large number of mammalian species from small bats up to bears are hibernators and play important roles in many ecosystems – denning in bears is actually considered true hibernation, since metabolic rates of torpid bears are as low as in other mammalian hibernators, such as ground squirrels.

Heather Johnson and colleagues investigated how changing environmental conditions affect hibernation behaviour. Most studies with this focus aim to investigate the impact of, for example, climate change on fitness and population dynamics in small mammalian hibernators. In general, however, studies finish here and do not go on to investigate how changes might impact other species in the same ecosystem and vice versa (e.g. predator-prey interactions). Johnson et al. found an elegant way to address this open question: They studied black bears and included humans in the calculation. First, they investigated the impact of access to food sources from humans on hibernation behaviour; second, they modelled whether changes in the hibernation behaviour of black bears are likely to affect human-bear conflicts. This is an interesting approach to understanding the manifold cascading effects that human development and climate change may have. These need to be considered if we want to manage wildlife successfully in a changing world.

The authors used GPS collar data from 64 adult females to measure activity for an average of three years and combined them with fine-scale, animal-specific habitat information. Besides natural food availability (seeds and berries), they included the availability of anthropogenic food and weather conditions (temperature and precipitation) into their model. Furthermore, they included individual parameters like reproduction, body mass, and age to investigate which predictors affected onset, duration, and termination of hibernation. It turns out that weather and food availability (both human and natural) had a major impact and additively shaped black bear hibernation behaviour. While high food availability postponed the onset and decreased the duration of hibernation, warmer temperatures also reduced the hibernation duration and led to an earlier emergence.

However, this is not the end of the story. The authors modelled the impact of changing hibernation patterns on human-black bear conflicts and on black bear mortalities. They show impressively that a prolonged active season might increase human conflicts with bears as well as mortality rates (e.g. car accidents, hunting). The authors point out that management agencies often assume that increases in human-bear conflicts reflect increases in bear densities, which would require countermeasures. Based on the results of Johnson et al.’s, study, this may turn out as a deadly wrong assumption for the bears.

Read the full article, Human development and climate affect hibernation in a large carnivore with implications for human–carnivore conflicts in Journal of Applied Ecology.

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