As part of a new study, researchers from North Carolina State University and N.C. Wildlife Resources Commission documented that female black bears (Ursus americanus) living in the limits of the mountain city of Asheville, North Carolina, were bigger than expected shortly after their first birthdays. These young female black bears averaged nearly 100 pounds – almost twice as heavy as bears living in rural forests.
Surprisingly, some of the young female bears in the city also had their first litter of cubs earlier than expected, at age 2.
The differences between urban bears and rural bears is important for understanding the ecology of black bears living around dense populations of people, where bears are exposed to mortality from vehicles and legal or illegal hunting activities, researchers said.
The study was completed as part of the North Carolina Urban/Suburban Bear study, launched by NC State researchers Chris DePerno, professor of fisheries, wildlife and conservation biology at NC State, and Nick Gould, postdoctoral research scholar at NC State. The work, which was done with support from the Wildlife Commission, aims to help us understand bear movements, reproduction, survival and causes of mortality. The objectives are to help wildlife managers develop science-based management decisions, and to help educate the general public about living with black bears.
The Abstract spoke with Gould and DePerno to learn more about their work.
The Abstract: When do black bears have cubs?
Gould: Across their range, which spans the North American continent, there have been anecdotal cases of black bears breeding in the first year they separated from their mom. Typically, black bears are born in winter dens in late December through early February. Generally, they breed for the first time in the summer at 3 and a half, and then give birth for the first time when they’re about 4 years old.
We found that some of these bears in Asheville are breeding earlier than expected at 1 and a half, and they’re giving birth for the first time at 2 years of age.
TA: What’s unique about how black bears reproduce?
Gould: Black bears are a unique species in that they exhibit delayed implantation. They breed in the summer months, but the blastocyst, which is a fertilized egg in a certain stage of development, doesn’t implant in the uterine wall until the fall. This gives bears a chance to feed in the summer when there are summertime berries, known as soft mast, and into the fall when there are acorns and nuts, known as hard mast, which are the primary food sources for most black bear populations. The general thought is that if these bears put on enough weight, they’re healthy enough to carry to term and reproduce, and if they don’t put on enough weight, for example when food is scarce, they can reabsorb the blastocyst. They save those energy reserves for themselves if there is not enough to carry the pregnancy and give birth.
TA: How long do bear cubs stay with their mom?
Gould: Black bears give birth to cubs that are fully dependent on mom. As the cubs grow, mom will begin to leave the den for short periods, but she won’t leave the den completely until the cubs have grown and are ready to follow. So, mom takes short forays to make sure the cubs can climb up and down trees, and when the cubs are ready and capable of keeping up with mom, that’s when the family group will leave the den.
The cubs typically stay with mom for about a year and a half. So, the moms will give birth in the den, and the cubs will stay with the mom for a full year. The cubs will den with mom the following winter (as yearlings), if she dens. If there are food sources available or even warmer temperatures, we’ve had family groups with yearlings stay active throughout the winter, with small periods of dormancy. After about a year and a half, in the summer months of June, July and August, these yearling black bears will disperse and leave the parental care of mom.
TA: How big do black bears get?
Gould: Throughout our study, we have captured and released some large adult bears. We captured an adult male bear that weighed 572 pounds in east Asheville. We captured another adult male bear that was 527 pounds on the Biltmore Estate just behind the mansion. The coastal population of bears in North Carolina includes the world record for largest black bear ever recorded. It was 880 pounds and legally harvested, or hunted, in 1998 in Craven County, North Carolina.
Early in the North Carolina Urban/Suburban Bear Study, we captured family groups consisting of yearlings and a sow, or mother bear. We were taken aback at first because we realized these young bears were pretty big. Some of the yearling male bears we captured and released weighed in excess of 200 pounds, and some of the yearling female bears weighed more than 120 pounds. We didn’t expect these young bears to be that big, at 1 to 1 and a half years of age. A healthy rural bear is typically between 40 to 75 pounds. That led us to examine whether these young females in particular were able to breed at 1 and a half years of age, and then sustain the pregnancy to give birth to cubs that would recruit into the population.
As part of our study, we determined that young female bears in the Asheville area were twice as heavy as the rural bears involved in the study. At the three forested rural sites (one in North Carolina and two in Virginia), the average weights for yearling female bears were about 23 kilograms, or approximately 50 pounds. The urban bears in the study were twice as heavy; they averaged 45 kilograms, or just about 100 pounds.
TA: Why is this important?
Gould: As we pull all these data together, hopefully we can help the N.C. Wildlife Resources Commission further develop management decisions for black bears, but, also, the citizens and residents of Asheville can become more educated on how to live responsibly in close proximity with bears. We’re tying in what we’ve learned in this first phase of the urban bear study with Bearwise, a public educational campaign to educate people to live safely and responsibly with bears.
DePerno: We designed a very comprehensive study to answer a lot of questions that the Wildlife Resources Commission had. We’re getting information on denning, movement, dispersal, survival, causes of mortality, home range, size and age at reproduction, which is what this most recent paper is focused on. To really manage a wildlife population, you need to understand the life history of the species you’re working with. We hope to be able to link research and management which is necessary to help the Wildlife Resources Commission with their management decisions.
