An adult male and an adult female black bear (Ursus americanus) were found in the same den in the Carson Range of the Sierra Nevada in Nevada. Co-occupancy of dens is very rare, and such behavior has never been previously reported for adult bears of opposite sex.
Goodrich, John M. and Stiver, San J.
"Co-occupancy of a den by a pair of Great Basin black bears,"
Great Basin Naturalist: Vol. 49
, Article 6.
Available at: http://scholarsarchive.byu.edu/gbn/vol49/iss3/6