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In a new synthesis publication, USGS researchers reviewed the documented and projected effects of climate on the ecology of black and brown bears in North America, revealing an increased risk of negative human-bear interactions.

Climate change poses a significant threat to humans and wildlife by altering the availability of resources such as food and habitat, which in turn can increase the frequency and severity of human-wildlife interactions. Negative human-wildlife interactions can take many forms, including property destruction, livestock depredation, and in extreme cases, threats to human safety. Human-bear interactions are a common problem and management priority for many wildlife and land management agencies in North America. American black bears are the most widely distributed bear species in North America and are frequently involved in human-bear interactions. Brown bears (referred to as grizzly bears in portions of their range), while much more limited in occupied range, are also implicated in human-bear interactions and share similar conflict drivers.   

Climate change has the potential to exacerbate the challenges of managing bears, as it may alter the availability of resources, with resulting impacts on bear ecology, behavior, and interactions with humans. While the existing literature provides a broad view of how changes in climate and weather affect bears, few studies have evaluated how those changes impact human-bear interactions, which is critical for effective bear management and maintaining human-bear coexistence.  

To bridge this information gap, researchers from the USGS National Climate Adaptation Science Center (CASC), Northern Rocky Mountain Science Center, and Alaska Science Center conducted a systematic literature review that was recently published in the scientific journal Biological Conservation. They reviewed 120 scientific papers that investigated how climate variability and change impact black and brown bears in North America, as well as the implications for human-bear interactions. The literature revealed that climate can affect many aspects of bear ecology, including diet, body size, habitat selection and use, denning timing, and population demographics. The primary way in which climate affects bears is through its impacts on when, where, and what types of food are available, which in turn affects bear diets, behavior, and demographics.  

Black and brown bears can adapt to a variety of habitats and foods, making them less vulnerable to climate change than some other wildlife species. But when these adaptive behaviors put them into closer or more frequent contact with humans, the risk of negative human-bear interactions can increase. For example, when droughts result in natural food shortages, bears may seek out alternative sources of food in areas of human development, such as easily accessible garbage, apiaries, or agricultural crops.  

This research provides a foundation for identifying climate drivers of bear ecology, conditions conducive to human-bear interactions, and adaptive management strategies. Given the influence of climate on different aspects of bears ecology, incorporating climate change considerations into bear management plans can help managers strategically allocate resources and promote human-bear coexistence. 

This work was supported by the National CASC project “The Effects of Climate Variability and Change on Human-Bear Interactions in North America.” 

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