Biologists warm up bear cub, bring it back to mother bear in new den.
It's not uncommon for us to get reports of black bear dens being disturbed in winter. Most of the disturbances are the result of logging activity or rabbit hunting (beagles find denned bears). In most instances, the disturbance is no big issue: it's just a matter of people staying out of the area – which most everyone is willing to do – to let a bear return to its den, or to allow a sow (female bear) to recover cubs and move to a new den.
But recently (February 2012), fellow biologist Will Staats and I received word of a three-week-old bear cub, one of 3 cubs in a litter, that had been separated from its mother. The cub, when we got to it, was lying near its original den, which had been (inadvertently) disturbed by a logging crew; its mother had moved 2 of her 3 cubs to a new den very close to the original, and left this one behind. The 1.5-pound bear was lifeless: we could detect no heartbeat or breathing, and its body temperature was very low.
I immediately placed the cub inside my warm jacket for the walk out of the woods. Back at the truck, we placed the cub on the heater. It took close to an hour, but eventually the cub started to move and vocalize. I took the cub's temperature about 2 hours after we picked it up, and it was at 90° F. (The internal temperature of a bear when not denning is around 100° F. Most of the adult bears that I have handled during winter (while denned) had body temperatures of around 90°-92° F, because their body temperature drops during this period of inactivity.)
I have had limited experience with hypothermic cubs, but I'm aware of instances where cubs have recovered once their body temperature was brought back to normal. So, I took the cub home that night to monitor its progress and keep it warm. At about 2:00 a.m., the cub was doing very well and was very vocal (crying). The cub, of course, was hungry, as it had not nursed in many hours. At 6:30 that morning, I returned the cub to the sow in her den. I'm confident that the mother bear accepted her cub back, and that it is well.
So what happened at the den site? Sows with newborn cubs have strong fidelity to their young, and if they need to move, they typically return and/or move the cubs to the new location. We believe that in this case, the sow did not pick up the cub because it was unresponsive. Had the cub been crying like its two littermates, I'm sure the sow would have moved it to the new den with the others. But nature is a tough place, and animal mothers have to focus on strong offspring; some level of cub mortality is the norm.
The logging crew that disturbed the den and reported the abandoned cub was very concerned for the bears' safety. The sow was denned in a hitch of wood cut last winter, which was being pulled out. Instead, the loggers left 2 hitches of wood in the woods, and stopped working in the immediate area of the den so as not to further disturb the sow and cubs.
Needless to say, this was a highly unusual event. We were able to help because we are trained wildlife biologists; we deal with live black bears regularly in the course of our work. The general public is advised to NOT pick up wildlife – in most instances, doing so is illegal. We are grateful to the logging crew for alerting us to the cub's plight, because we were able to literally bring this one back to life and return it to its mother. We try to closely monitor a bear den disturbance when it involves a sow with cubs, to ensure that she does return to the cubs. In most instances, giving the family group some space is all that is necessary. The sow does the rest. As wildlife stories go, this one has a happy ending.