Predation by Other Species
Very little is known of predation on cubs. Cubs sometimes
weigh less than 2 kg when they leave their natal dens, and
they sometimes are left unattended while their mothers forage
(unpublished data). Several common predators are capable of
killing cubs (Nelson 1957, Rogers 1977, Rogers and Mech 1981),
but adult black bears are practically immune to predation from
all North American animals except grizzly-brown bears (Ursus
arctos) and timber wolves (Canis lupus). Black bears are
scarcely sympatric with polar bears (Ursus maritimus).
Grizzly bears are widely believed to prey on black bears but
the frequency of this is unknown (Rausch 1961). Several authors
have presented evidence that black bears avoid grizzlies (Barnes
and Bray 1967, Jonkel and Miller 1970, Herrero 1972, Martinka
1976) or the preferred habitat of the grizzly (Burroughs 1961,
Jonkel 1967), with some exceptions (Lloyd 1978).
Black bear home ranges commonly overlap those of timber
wolves and coyotes (Canis latrans). There are several reports of
predation by these species on female or young bears but not on
adult males. C. C. Dickson (Personal communication, 1980) found
that wolves killed an immature black bear in northern Ontario on
18 May 1979. Boyer (1949) reported coyotes killing a yearling
black bear, and Young and Goldman (1944) presented a trapper's
description of wolves killing a black bear of unknown age and
sex. Schorger (1949) related an 1858 newspaper account of wolves
killing a trapped bear in Wisconsin.
Data indicate that predation by wolves on black bears is
uncommon. During radio-tracking in northeastern Minnesota, only
one radio-collared bear was killed by wolves. In that case, a
16-year-old, 72-kg female and her newborn cubs were killed at
their den in mid-February 1977 (Rogers and Mech 1981). Analyses
of wolf fecal droppings further indicate low predation on bears.
Of 1,449 wolf droppings collected in northeastern Minnesota, only
19 (1.3%) contained bear remains (Byman 1972, Frenzel 1974) and
at least 16 of the latter were collected near a residential area
where bears had been shot (D. Ross, personal communication,
1979). In central Ontario, Voight et al. (1976) also found bear
hair in a very few (number not given) of 1,943 wolf droppings.
Again, most of the droppings containing bear remains were
collected near residential areas, suggesting scavenging of bears
killed by gunshot (G. Kolenosky, personal communication, 1979).
However, in late August 1982, a well-nourished cub became missing
from a radio-collared female in Minnesota, and later that month a
wolf dropping containing cub claws was found in her territory.
Additional study of cub mortality is needed to determine the
extent to which cubs are preyed upon.
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