Bears as Predators ~

[brotherbear]

Grizzly bears hunting musk ox...
pubs.aina.ucalgary.ca/arctic/Arctic35-4-545.pdf

Muskox Bull Killed by a Barren-Ground Grizzly Bear,
Thelon Game Sanctuary, N . W. T.
ANNE GUNN’ and FRANK L. MILLER

INTRODUCTION
Muskoxen and barren-ground grizzly bears are relatively
common along the banks of the Thelon River in the
Thelon Game Sanctuary. In June 1981 we were flying a
helicopter search of the Thelon River area during a study
of water crossings used by barren-ground caribou (Rangifer
tarandus groenlandicus). In the early afternoon of 23 June
we were flying eastward when we spotted a grizzly bear
standing on its hind legs among willow (Sulix spp.) bushes
in a clearing surrounded by black spruce (Picea mariana)
on the north shore. As there were two gulls (Larus spp.) in
attendance, indicating the possibility of a kill, we circled
closer and could then see a dead muskox on the ground
near the bear. The grizzly bear alternately reared up and
dropped onto all fours as we came close and when the
helicopter was about 100-150 m away, the bear galloped
away.
We landed near the carcass of an adult muskox bull
lying on its left side. The carcass was intact except for
some exposed flesh and head wounds. The nose was tom
away and the nasal turbinal bones were crushed and the
cartilage torn. The right ear was split and torn away at the
base where there was a penetrating wound into the skull.
Traumatized areas were hemorrhagic, indicating that the
wounds were inflicted on a living animal. The hide and
musculature had been removed in the lumbar and thoracic
areas, exposing the vertebrae and the right scapula. The
internal organs were still intact and warm to touch. Subsequent
histological examination of the dental annuli of a
first incisor indicated that the muskox bull was 9-10 years
old.
The greening sedges (Carex spp.) immediately around
the carcass were trampled and we backtracked along a
disturbed path to a heavily trampled area of 5 m in diameter
about 15 m away. The willow bushes peripheral to that
trampled area were flecked with blood clots and clumps of
blood-stained muskox wool.
The ground cover was beaten down and the ground
surface disturbed in many places with footprints pushed
10-15 cm or more into wet soil. We suggest that the grizzly
bear surprised the muskox bull while it was grazing on
sedge (indicated by rumen contents). The bear most likely
grabbed the bull above the muzzle. In response, the bull
must have braced its front legs and tried to dislodge the
bear, suggested by front-foot hoof prints driven deep (15
cm) into the churned-up ground. Either the bull collapsed
or the bear swung him off balance. At that point, the bear
probably transferred its bite to just below the back of the
bull’s horn boss. After making the kill, the bear dragged
the carcass to where we found it, and had begun feeding
when we interrupted. We returned about 48 hours later
and found a light grey wolf (Canis lupus) and a grizzly bear
whose colouring suggested it was not the bear that had
made the kill. The carcass was dismembered and had
settled into the wet ground. Most of the muscle masses
and the internal organs had been consumed and the limb
bones were scattered around the hide. The rumen had
been pulled from the carcass but had not been fed on.
The destruction of the facial area was also the mode of
attack of a barren-ground grizzly bear killing a caribou
cow whose carcass we found on the Beverly caribou herd’s
calving ground, northeast of the Thelon Game Sanctuary,
in June 1981. Griffel and Basile (1981) described puncture
wounds in the frontal or jugal bones of 109 of 332 bearkilled
sheep (Ovis aires) in Idaho. The facial area is richly
innervated, and Mystervd (1975) in Griffel and Basile (1981)
suggested that unconsciousness and hypoxic asphyxiation
would follow severe and sudden injury to that area. Also,
the seizing of the muskox bull’s muzzle would reduce
chances of the muskox using its horns to gore the bear and
increase the bear’s chances of throwing the muskox off its
feet.
Solitary muskox bulls usually seem particularly alert,
and their speed of response, size, strength, thick coat and
horns must combine to make them a formidable quarry
even for a grizzly bear. The location of this kill, at the edge
of a small clearing where ambush by rushing from nearby
cover was possible, suggests that the kill was opportunistic.
The muskox bull was probably so intent on foraging on the
new growth of sedges 10-20 cm high that he was not aware
of his attacker until it was too late. The femoral marrow fat
was pinkish-white and firm, suggesting good nutritional
status, and we did not observe any obvious infirmities that
would have made the bull particularly vulnerable.
Tener (1965) summarized predation on muskoxen and
noted that Pederson’s report of a possible kill by a polar
bear (Ursus rnaririrnus) may be the only reported instance of
bear predation. He further commented that predation by
barren-ground grizzly bears is rare, since up to 1965 only
Hornby (1934, in Tener, 1965) had observed bears feeding
on muskoxen on the banks of the Thelon River. In the late
1970s A.M. Hall (pers. comm.) observed grizzly bears
feeding on muskox carcasses along the banks of the Thelon
River (see photograph of grizzly bear sleeping near partiallyeaten
bull muskox in Hall, 1980). In 1978, on the banks of
the Thelon, Hall observed three muskox carcasses on which
grizzlies had fed, but he could not determine whether the
bears had killed or were scavenging the muskoxen. Hall
(pers. comm.) believes that grizzly bear predation on
muskoxen is high, especially on solitary bulls along the
Thelon River, probably because the dense willow stands
favour surprise ambushes. In June and July 1981, we saw
only solitary bull muskoxen feeding in the willow stands,
which leads us to the same supposition. Within 40 km of
the carcass described in this paper, during the same flight,
we observed five other grizzlies on the north shore. Pegau
(1973) briefly described an apparent kill of a 2- or 3-yearold
muskox by a bear but the carcass was almost completely
consumed, so scavenging could not be ruled out.
The carcass was found on the Seward Peninsula, Alaska,
where Grauvogel (1979) speculated that the slow rate of
increase of the transplanted muskox herd might be partially
attributed to grizzly bear predation on muskox calves,
though no evidence was cited. Our account of an apparently
healthy, prime adult muskox bull that was killed by a
grizzly bear is the first documentation of such an event. Reply