After the recent meeting of the IUCN’s Bear Specialist Group and the International Association for Bear Research and Management in Provo, Utah, I explored some bear habitat between Provo and San Diego and was reminded that one bear species in North America is an example of great conservation success: the American black bear. The IUCN (International Union for Conservation of Nature) maintains the Red List of Threatened Species, which is a global list of species and their conservation status. The American black bear Ursus americanus is listed as a species of Least Concern, primarily for two reasons. First, overall there are a lot of black bears. There may be twice as many American black bears as all the other bears in the world combined! Second, most populations of American black bears are stable or increasing, making this a great story of how a species can recover through conservation action and human tolerance. Some local black bear populations are not doing very well, but overall the prognosis for the species looks fantastically better than it did 100 years ago.
When European settlers reached North America, black bears were found throughout much of Canada, the US, and northern Mexico. There are once again black bears in most of those areas. However, there was a great decline in the number and range of black bears until the early to mid-20th century. In fact, I think that if the IUCN Red List had existed 100 years ago, the reduction in numbers and range of the American black bear would have led it to be listed as Endangered, which is the same category of conservation concern as the giant panda is now!
What led to such a dramatic decline in American black bears? The main causes were habitat loss, habitat fragmentation, overhunting, and conflict between humans and bears. These are the same issues that still threaten most of the other bear species. It’s taken decades and a lot of effort by many national, state, and provincial governments, conservation organizations, scientists, educators, and citizens, but the recovery of the American black bear illustrates that conservation of bears can succeed.
How did the recovery happen? A wide variety of actions were taken in support of American black bear conservation, including habitat protection, changes in bounties and hunting laws, changes in programs mitigating human-wildlife conflict, and more intensive efforts such as translocations and reintroductions. It’s also helped that this bear is an omnivorous habitat generalist, so although it is restricted to forested habitats, it can and will learn to eat a wide variety of foods, and it can live in fairly dense populations. That means that a population of American black bears can survive in an area that would be too small to support a population of brown bears.
Researchers with San Diego Zoo Global have collaborated with others to investigate various aspects of the physiology and behavior of American black bears, both to understand this species better and as a means to better understand other bear species. Doctors Barbara Durrant and Tom Spady have described the seasonally polyestrus, promiscuous mating system of the American black bear, showing that ovulation and conception occurs in each of a black bear female’s estruses during a breeding season. DNA analysis of preimplantation embryos proved that if a female mates with more than one male during the same mating season, the cubs born in her litter may be maternal half-siblings and not full siblings. Barbara and Tom also investigated the potential use of the hormone leptin as a wildlife management tool to monitor the adiposity (fatness) of American black bears and found that serum leptin measurements markedly improved the resolution and accuracy of common field estimates of body condition in this species.
A sign in the Olympic Peninsula of Washington reminds people hiking and camping in the forest that their behavior can have negative consequences for bears.
Did you know that bears hum? Megan Owen has worked with others to study humming by bears, which occurs in all bear species but the giant panda. Most humming is done by cubs and is generally associated with suckling; however, the exact function of this behavior is still unknown. The relative loudness and very persistent nature of humming are puzzling! Further, we still don’t know whether the hum is an acoustic signal or whether its associated vibration physically stimulates the mother, perhaps enhancing milk production. Megan has also researched the interactions between mothers and their young cubs, in hopes of developing a better understanding of maternal care behavior and the range of variation associated with maternal care and cub behavior. Understanding this process in black bears may help us better understand the process in other bear species as well, including brown and polar bears.
Although the overall picture looks good for American black bears, as populations of both bears and humans have grown, new conservation challenges have developed. Because American black bears are fairly quick to learn to feed on new food sources, whether or not those food sources are “natural,” black bears learn to feed on foods they get from humans, whether the humans want them to or not. This leads to new conflicts as the bears use their intelligence and strength to seek the most profitable food source available. If you are fortunate enough to live or recreate in bear country, you can help bears and bear conservation, and avoid damage and risk from food-habituated bears, by ensuring that bears don’t get access to any human sources of food. That includes foods like pet foods, seed in bird feeders, greasy barbecue grills, garbage, etc. With your help, the support of citizens like you, and effective conservation actions, the American black bear can continue to be a great conservation success story.
Russ Van Horn is a scientist with the San Diego Zoo Institute for Conservation Research. Read his previous post, Whimsical Bear Ambassador Arrives.