Hobbies And Interests
Limted Food Supply
Before settling in to hibernate, black bears start a hyperphagia period during late summer and fall when they eat continually to increase their weight and fat content. Lynn Rogers, director of the Minnesota's North American Bear Center, calls it their "eat-eat-eat mode." Climate change is affecting rainfall in northern black bear habitats. Drought is limiting the size and growth of the plants and fruits black bears bulk up on before hibernation. Some bears begin hibernating early without the proper nourishment to sustain them through the winter.
Less Time Sleeping
Canadian environmental officials predict that black bears will react to climate change by migrating north to colder climates. Even with the move, warmer overall temperatures could cause black bears to cut short periods of hibernation. With bears spending more time awake, foraging and competing for food, the animals put more pressure on food supplies and risk shortages. Changes in rainfall related to global warming could also stunt berry crops, a major source of food for black bears in Canada.
Risks of False Spring
As black bears prepare to enter their dens to hibernate, they can pack on up to 30 lb. a week. However, as they sleep, the animals lose up to 30 percent of their body weight. Females who give birth during hibernation and wake up occasionally to care for their cubs, lose up to 40 percent of their body weight. When they wake up and leave their dens in spring, the females are weak and lethargic. When abnormally warm temperatures fool bears into ending their hibernation early, they return in a vulnerable condition to a habitat where plants haven't sprouted and food isn't yet available. Starvation and attacks by predators, mainly humans, are a greater risk.
Delayed Climate Signals
Black bears begin slowing down several weeks before hibernation. They usually stay nearby their dens, sleeping and waiting for a cue from the weather to move inside and fall asleep. Some bears wait till the temperature drops to enter their dens; others move inside after the first snow. Climate change is delaying the onset of these natural signals to bears, causing them to remain outside of their dens -- lethargic and vulnerable to hunters, dogs and grizzly bears.
Reproduction
When drought, wildfires, flooding and other global warming trends limit the food supply, some black bears begin hibernating early. Entering a den before gaining enough weight can be a problem for pregnant females. Bears mate during the spring and summer. Although females carry the embryo, it doesn't implant in their uterus and begin to grow until December, after hibernation has started. Embryos will not grow in females who have not gained enough weight to nourish them. Cubs that are born despite malnourishment may die because mothers are unable to nurse them.