Black bears in the Backyard: Adapting to a New Kind of Wild

Cities are a special environment regulated by humans: planted green spaces, paved streets, large buildings, constant light and traffic. Some animals like meadow birds have disappeared from these landscapes, but other animals have not. Trashcans, littering, bird feeders, food laying around restaurants and cafés all attract animals to the cities. This leads to an increase in conflict between especially large carnivores and humans. In western North America, the black bear (Ursus americanus) is one of these large carnivores. They are famous for visiting everyone’s yards searching for garbage and taking a dip in garden swimming pools. Despite the relatively new urban environment, black bears living in these environments show some behavioural and ecological changes caused by differences in food resource availability compared to that in natural habitats (Beckmann & Berger 2003a).

Activity of the black bear

Interestingly, black bears living in urban areas showed a shift in their activity from diurnal to crepuscular and nocturnal. Beckmann & Berger (2003a) found that bears living in natural areas started their day around 8 o’clock in the morning. Urban bears, by contrast, began their activity at the end of the day, around 7 o’clock in the evening. These urban bears were active for about 8.5 hours, while non-urban bears took about 13 hours a day. These changes in behaviour are probably caused by human disturbances, although food sources play a role too. The high amount of food sources in urban areas causes bears to reach their maximum caloric intake faster than non-urban bears. They even stopped their daily activity while garbage was still available, meaning there is more food available than they require. They have to spend less time foraging, meaning less activity time.

Another aspect of black bear activity is the time they spend in their den to overwinter. Urban bears seem to enter their den later than non-urban bears. This is on average a 1-month difference: early January for urban bears compared to early December for non-urban bears. Some urban bears do not even hibernate at all. The dates the bears leave their den, however, do not differ. Adult male bears are the first ones to exit their den in March and early April. The last ones are the adult females with cubs of the year, leaving their den early April to May. With this difference in entering date but the similarity in exit date, urban bears spend less time in their den to hibernate (Beckmann & Berger 2003a). The urban environment possibly plays a role in this: it provides enough food sources and has higher temperatures than the natural areas. This all could make it less necessary to hibernate to survive the winter.

More black bears in the city

The high availability of food in urban areas shows more effects. For male bears for example, there is a reduction of 90% and for females a reduction of 70% in home-range size. This leads to a higher density of black bears in urban areas than in non-urban areas. But when looking at the sex ratio, it is completely out of balance with many more males than females. Additionally, male urban black bears show an increase in body size of 20% and females an increase of 50% compared to non-urban conspecifics. Urban females also had more cubs which is a possible result of this body size increase (Beckmann & Berger 2003b).

A “problem” bear

Despite several behavioural changes of the black bear in urban areas to avoid human disturbances, bears are often called a “problem” bear, with the consequence of being killed. Surveys done by Booth & Ryan investigated how people think about these bears in British Columbia, Canada. Luckily, residents support the presence of this wildlife in the city more and more and are willing to change some personal measures to avoid bear-human conflicts. These measures are for example the picking of fruits from trees in their gardens or putting the garbage out at the right time on collection days. With less attractants for bears to come close to people, there is a smaller change of creating a “problem” bear (Booth & Ryan). So, if the changes come from both sides, people and bears can both live happily in urban areas.

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References

Beckmann J.P. and Berger J., 2003a – Rapid ecological and behavioural changes in carnivores: the responses of black bears (Ursus americanus) to altered food. J. Zoology 261, 207-212. https://doi.org/10.1017/S0952836903004126

Beckmann J.P. and Berger J., 2003b – Using Black Bears to Test Ideal-Free Distribution Models Experimentally. Journal of Mammalogy 84, Issue 2, 594–606. https://doi.org/10.1644/1545-1542(2003)084%3C0594:UBBTTI%3E2.0.CO;2

Booth A.L. and Ryan D.A.J., 2019 – A tale of two cities, with bears: understanding attitudes towards urban bears in British Colombia, Canada. Urban ecosystems 22, 961-973. https://doi.org/10.1007/s11252-019-00873-7

Featured photo: © Michael Seraphim, Colorado Parks & Wildlife