Two female grizzly bears in Grand Teton National Park have apparently traded one of their cubs. For tracking purposes the mother bears have been named 399 and 610, and since mid-July 610 has been seen with an extra cub. Prior to this time 610 was observed with two cubs, but since then she has had three. No one knows exactly what caused the mother bears to swap cubs, but it could have been a dramatic event like an attack by a male grizzly bear on the cubs. Sometimes they kill cubs in order to make a female grizzly more likely to mate. Another speculation is that mothers and cubs sometimes get separated when the mother is hunting and it may have been the two mothers were hunting elk in the same area. When they went looking for their cubs again, the exchange happened accidentally and was accepted by both mothers. Mother bear 610 will now have to find enough food and make enough milk for three cubs. Another possibility is that mother bear 399 is suffering from an illness or injury that has made her less able to find food and produce milk so one cub was not getting enough to eat and attached itself to another mother bear. Fortunately mother 610 did not reject the third cub.
In an Australian national park, sometimes mother kangaroos allow a joey from another female into their pouch and then take care of them for weeks or months. Normally kangaroo mothers reject joeys that are not their own. A research project in the park though has documented a five percent adoption rate for the 134 juveniles the have tagged and documented. Close biological relatives of mothers with offspring have been ruled out as the adopters, so it isn’t just sisters helping each other.
Several years ago near Jackson Hole, a hunter shot and killed a female cougar, leaving three orphaned cougar kittens to die. This scenario is not uncommon as hunters can’t identify the gender of a cougar when they are hunting them, and therefore are going to kill females with kittens sometimes. Generally when they kill a female, that means they also killed the kittens if there are any, because once motherless, the kittens can’t feed themselves. Three orphaned kittens, however, were adopted freely by another female cougar in the area that already had three of her own. She allowed them to play, sleep and eat with her own family. An ecologist speculated the hunter had killed the mother of the female cougar that adopted the three, and therefore the adoptive cougar was taking care of kittens genetically related to her and her own kittens. This may be the case, but the Australian researchers were convinced they were seeing adoptions performed by mothers genetically not related to the young.
Image Credit: Mila Zinkova