BROWN BEARS: HANDLING AND INGESTING FISH PREY

In the video featured above, you will see various fishing methods and some of the handling methods described in the article below. A few things to look for: there is a sequence of video that shows a big brown bear deftly removing the brain from a fish. There is a scarred, big boar diving into a deep river pool from the shoreline and submerging in an attempt to capture its slippery quarry (he finally succeeds in capturing a "spent" fish in the video and stands on its hind feet as it tears the fish apart). Toward the end of the video, you will see a large boar launching some of its great bulk from the river and plunging back into the water with fore legs outstretched. At one point, it has herded a big school of salmon along the river bank and appears to be trying to push some of the fish onto the shoreline. Turn up the sound and enjoy!

Grizzlies use a number of different handling techniques when feeding on salmon. In most cases, the savvy “fisherbear” will grasp its prize in its jaws and carry it from the waterway to the shore, a gravel bar or surrounding grassy meadow/woodland (subordinate grizzlies, in the presence of conspecifics, are often more likely to move farther from the capture site than larger, more dominant bears). They then place their catch on the ground and stand on it with the fore paws. How the prey fish is processed may vary from one individual bear to the next or from one location to another. In many cases the first thing a bear will do is bite down on the posterior region of the fish and remove the tail section. Another body tissue targeted early in the handling process is the skin. To skin its quarry, the bear will grasp the skin with the incisors and pull upward, peeling the integument from the salmon’s body.

If food is in short supply (e.g., it is early in the salmon run or if fish numbers are down) the bear will consume the entire fish. If food is abundant, the bruin may select the choicest parts of the fish and leave much of its behind for scavenging birds, other mammals or even other bears (e.g., subordinate individuals or those that are poor at fishing). As mentioned in other posts, the skin is preferred as are the brains, but rather than ingesting the entire head, the bear often bites through the top of the cranium and laps out the brain or plucks them out with its incisors (see video footage above).

Not all bears take the time to leave the stream to eat their prize. It is not uncommon to see a bear, standing in knee deep water, clamping the fish against the front foreleg with the opposite paw (some bears employ this technique when eating fish on shore). The bear then rips the fish apart, one bite at a time. If the water where a fish is captured is shallow enough, some bears will pin the fish to the stream bed, while in a state of repose, and then stick their head underwater and rip pieces from their piscine prize (the bear will raise its head to masticate and then submerge to take another bite).

I have noticed that in many cases the fish rarely struggle much after being trapped in the bear’s jaws. They seem to go limp. They may flop about if the bear should drop them on the shore before pinning them down to eat, but otherwise they resist very little while in the jaws of the bruin. (I did see occasions where they fish would struggle if a bear bit down on the upper back.)

© Scott W. Michael

2008 KATMAI BEAR TRIP REPORT: PART 4 (GEOGRAPHIC HARBOUR - INDIVIDUAL BEARS)

A sow with her older cubs attempts to teach them to fish, although they prefer to play and loot their mother's catch.

Geographic Habor’s fishing grounds were also home to a vivacious family unit, consisting of a sow and a pair of ~ 2 1/2 year olds. The mother was an efficacious “fisherbear,” while her cubs did little fishing. Instead, they spent much of their time grappling with each other like hairy Sumo wrestlers! When they were not playing, they were shadowing their mom and stealing any fish that she hauled in. Most of the time she would let them take off with her catch, although she did occasionally attempt to wolf down some of her piscine prey before she was looted by her greedy brood. On one occasion she lost her patience and cuffed one of her overzealous offspring before giving in and letting go of her fish (see video below). Occasionally, the two hooligans attempted to include mom in their frolicsome behavior. She complied a couple of times, jawing at her young assailants.

A trio of grizzlies: a sow with her two offspring (these to youngsters are probably 32 months old). Note how she does all of the fishing, while they benefit from the fruits of her labor! Compare these two laggards with the adolescent fishing machine below.

In contrast to these impish, 2.5-year olds, we observed an amazing young bear that was a fishing machine! This bruin was a ~ 1.5 year old (usually referred to as a yearling) with a light colored (nearly blonde) mother. The pair initially made their presence known when the mother, with the cub trailing behind, were observed chasing another bear. They gave up their half-hearted chase and began to slowly meander toward the prime fishing area. Once they arrived at the river bank, it was not long before the yearling was chasing and even catching salmon! (There were few other bears in the area at the time.) The mother bear seemed to lag behind the young bear, keeping close enough to protect its progeny if the need arised, but yet far enough away to allow it to learn some life skills. The young bear was such an enthusiastic piscator that at one point it had a fish in its mouth, while it attempted to capture a second salmonid (see the video below)!

The fishing exploits of an ~ 1.5-year old (yearling) bear - this young bruin was a very effective fisherman, as you will see in the video above.

© Scott W. Michael

MARINE MAMMALS ON THE MENU

A veritable brown bear buffet! Photo taken by Scott W. Michael.

It looked like a big, white amorphous blob at first glance, but after further investigation one could make out the mouth-end of the beast, the flukes and flippers. It was a humpback whale that had washed up on the shore of Fort Abercrombie State Historical Park, Kodiak (Alaska) about a week before we searched it out. We had heard reports that the whale had been deposited by winds and waves on the Kodiak coast, but finding the rotting blubber-laden beast was to prove a bit of a challenge. When we visited the local rangers station, they didn’t seem too eager to tell us where it was. After further probing, they finally shared the approximate location. As we left the office, a ranger mumbled “Watch out for bears.” We concluded this is why they were hesitant to share the cetacean’s resting place - they did not want to have to deal with a problems that can occur when people and food hoarding bears cross-paths.

It turns out that dead whales are a favorite of coastal brown bears in parts of coastal and insular Alaska. The tons of rotting blubber, flesh and whale organs can produce an olfactory beacon that can reach the nasal epithelium of a brown bear many miles away (there are anecdotal accounts of bears smelling putrid whale from 20 miles away). The culinary tastes of a brown bear are not that refined, and besides whale flesh has lots of nutrients that can help a bear lay down fat for the denning period. The only drawback to eating a dead whale is the flesh can be hard to handle. The skin is so tough that even a massive brown bear can have a difficult time tearing a chunk free and masticating it. (The blubber layer of a whale’s flesh can be as thick as 43 to 50 cm!)

A whale carcass can attract many bears, as was the case on the California coast centuries ago. In the book “California Grizzly” (1955) the authors share the following:

Those (ed. grizzly bears) living near the seacoast were attracted to the bonanza supply where ever a whale washed ashore – and the one-time abundance of whales in our coastal waters probably made this a not uncommon event. The first reports of bears eating this food was by the Vizcaíno party at Monterey in 1602; a very large whale had gone ashore, “ and the bears came by night to dine on it” (Wagner, 1929). Revere (1849) wrote that the carcass of a whale, thrown upon the beach, will attract a “regiment of bears” – and Kotzebue (1921) used the term countless “troops.”

On the shores of Kodiak Island and along the Katmai coast, groups of brown bears feed on moribund whales, while on the Kenai Peninsula, bears of various age classes are reported to move to Bristol Bay to scavenge on dead gray whale (Eschrichtius robustus) (Glenn and Miller, 1980). In the Yukon, grizzly bears have been observed to scavenging on Beluga (Delphinapterus leucas) carcasses. Troyer (2005) reports seeing 12 bears feeding on a gray whale carcass at the same time (there were 18 bears in the immediate vicinity). He states that all of the bears worked over the carcass, only occasionally engaging in brief altercations during the feast. Some bears would leave, only to have their place taken over by another bear. Bear continued feeding on it for a week, at which time the remains of the carcass were carried away by the tide. There are reports of observers seeing brown bears entering or appearing from a hole in a large whale carcass. Apparently, the bears entered the bloated whale to feed on the internal organs or chew at the muscle from the inside. After gorging themselves with whale flesh, brown bears may roll on the odoriferous carcass. The function of this behavior (which, unfortunately, is also a habit they share in common in domestic canines) is not known.

Brown bears occasionally capture live pinnipeds, like these harbor seals. Photo by Scott W. Michael

Not only are moribund marine mammals consumed, brown bears have actually been known to captured and kill pinnipeds. Of course, polar bears are well known form their seal-eating habits. They have developed hunting strategies and physical adaptations to effectively exploit this resource. Grizzlies, on the other hand, feed on these animal opportunistically. If a hungry bear encounters a hauled out seal that it can get to before the latter can reach the water, it may attempt to subdue it. For example, grizzlies have been known to eat harbor seals (Phoca vitulina) along the Alaskan Peninsula and in the Northwest Territories of Canada. They are more susceptible to bear attack than some other pinnipeds (e.g., sea lions) because they are much more cumbersome and would have a more difficult time escaping if they are too far from the water’s edge. Seals are also more likely to be found along sandy shorelines, where bears sometimes hunt. That said, in most cases, seals haul out on small islets along the shore – habitats that are not often visited by grizzlies. There are also rare reports of big coastal brown bears taking on walruses (this has been reported on the Kenai Peninsula) (Glenn and Miller, 1980).

(Unfortunately, it turned out we never did encounter any bears on the Fort Abercrombie humpback carcasses the day we visited it, but I would not be surprised if it was eventually located and fed upon by opportunistic brown bears.)

References:

Glenn, L. P. and L. H. Miller. 1980. Seasonal movements of an Alaska Peninsula brown bear population. Int. Conf. Bear Res. And Manage. 4:307-312.

Check out these videos of brown bears feeding on dead whales:

A group of brown bears feeding on a whale carcass on coast of Kodiak Island, includes wallowing on dead cetacean (please pardon the silly commentary). Click here.

© Scott W. Michael

EARTH-EATING – GEOPHAGY IN BROWN BEARS

Grizzly bears intentionally ingest earth, which may serve several different functions.

In a famous quote about the food habits of the grizzly, naturalist John Muir states that these bears “eat everything but granite.” It turns out that Muir’s statement is not quite right, as while they have not been documented to eat rocks, they will eat earth! Some of the soil found in grizzly scat is not doubt ingested unintentionally along with their normal foods, like roots and ground squirrels. But grizzlies also intentionally eat soil and river sediment.

There are a few anecdotal accounts of brown bears diving down in the river ways in which they fish to take mouthfuls of mud from the river bottom. It has been suggested that they do this to clean their alimentary tracts of internal parasites. At Katmai National Park, we found brown bear scat that was comprised of fine sediment. The fecal material also contained numerous worms (I cannot be sure of the identification of the parasites involved, but they looked like a type of nematode).

In Yellowstone National Park, Mattson et al. (1999a) found 12 sites where grizzlies consume soil and found earth in some scat samples. These areas were free of vegetation due to thermal activity. Geophagy was most common between March and May and again from August to October – these correspond to times when ungulate and mushroom eating was also common. The researchers concluded the soil consumption may have several functions. Like ungulates, grizzlies may eat earth to detoxify secondary compounds present in the foliage they consume and to supplement their diet with potassium. In the areas where grizzlies ingested soil, the earth has very high in potassium, magnesium and sulphur. The authors also suggest that that by consuming these soils, the bears may prevent diarrhea by helping to get rid of some parasites and bacteria in the alimentary tract.

References:

Mattson, D.J., G.I. Green and R. Swalley. 1999. Geophagy by Yellowstone grizzly bears.
Ursus 11:109-116.

BROWN BEAR FISHING BEHAVIOR: PREY SELECTION

A big brown bear with a big salmon. There is more to the fishing behavior of Ursus arctos than meets the eye! Photo by Scott W. Michael.

“In small backwaters where the fish collect in shoals and where the fins of the fish are visible while they move against the current. The bears either enter the water attempting to drive the fish into the shallows, or stand in the water, lowering the head to the surface while waiting for the fish and catching it rapidly with the paws.... The catching of fish is easier in spawning places with calm water, where the fish are less cautious and strong. When the fish are numerous the bear eats mainly the head and part of the back, when fish are scarce, they are eaten completely. The stomach of a large bear may contain 20 kg of fish. However, plants and berries are always found together with fish.” Yu. V Averin (1948) describing the feeding behavior of the Russian brown bears in the Kronoki reserve (in Stroganov 1969)

As far back as 1889, bear-watchers reported that bears selectively ate parts but not all the salmon they caught. A. M. Nikol’skii (in Stroganov 1969) stated that when fish are abundant, Russian brown bears eat only the head and roe of the salmon, leaving the body. When the fish are scarce, they consume their entire catch. Yu Averin, in the 1948 quote above, also reported on this phenomenon.

Most salmonids are anadromous. That is, they hatch in freshwater, move into the sea, and return to the freshwater streams where they hatched to spawn themselves. While it varies from one species to the next, in many parts of Alaska, three different species of salmon spawn during the months of July through early October. The salmon enter their spawning grounds and typically live in freshwater for 5 to 25 days (depending on the species and location) until they die of senescence. Many die before this time as a result of bear predation. In one study, of 1,933 salmon tagged by researchers as they entered three different Alaskan streams, 64 % of the tagged fish were killed by bears, 33 % died of senescence, and 2.6 % died from other causes (like stranding on the beach or were killed by other predators).

When a salmon makes its way into freshwater, it stops feeding and expends incredible amounts of energy on reproduction and the act of swimming upstream – as a result, from this point forward the nutrient value of a fish will drop as they burn stored fat and protein. Researchers Hendry and Berg (1999) found that the total energy content of a salmon drops from 40 to 50 % and the lipid content plummets as much as 80 to 95 % from the time the fish enter a stream and the time when they die of senescence. It would make sense then that brown bears would attempt to capture and consume those fish that have spent less time in Alaska’s streams and that the fish that the bears find least attractive would be those that are reproductively spent and in the process of dying.

But how could a bear determine the nutrient value of a fish (e.g., how long it had been in freshwater)? In some salmon species there are very overt signs of senescence. For example, male red or sock-eye salmon (Oncorhynchus nerka) develop hooked jaws during the spawning period. Salmonid energy stores are depleted and the immune system begins to suffer, as a result of stress and malnutrition, the skin becomes discolored and patches of fungus appear. The longer a salmon is in freshwater engaging in the spawning process, it picks-up more wounds on the body from fighting and frayed fins as a result of nest digging. So, it maybe that these outward signs of a salmon’s physical condition (potential energy content) could be used by grizzlies to help select the most valuable prey.

Researchers have examined if brown bears target those fish that have been in freshwater for a shorter period of time (“younger” fish) and thus have greater nutrient content. They found that in streams where bears can easily capture salmon that they do select younger salmon. In one such stream, the bruins fed most heavily on fish that have been in the stream for three days or less, while they totally ignored fish that had been in freshwater for over 12 days. However, in streams that were wider, had deep pools and/or lots of structure (e.g., sunken limbs and overhanging banks) brown bears fed more on “older” fish (individuals that have been in the stream for over 12 days). In these streams, the salmon that have recently entered freshwater are more energetic and better able to elude the bears, while “older” fish that have expended lots of energy and are “on their last fin” are easier to catch. While the “younger” fish may have more nutrients, the bears will expend more time and energy to catch them. Therefore, in these streams, going after the less elusive, but less nutrient-rich fish, is a better strategy.

Other factors that will impact brown bear foraging strategies are the density of fishes in a particular stream and the weather. When the streams are chock-a-block with amorous fish, the bears can be more selective, while if the fish are few and far between, they cannot afford to be as particular. Likewise, if the streams are breaking their banks and the water is turbid as a result of excessive rain, bears are not as selective. It is get what you can, when you can! There are also individual bears that apparently develop a taste for rotting salmon carcasses. Bledsoe (1987) tells of a bear named “Zubin” at McNeil Falls that would leave a good fishing spot to go scavenge for dead fish.

Food handling in brown bears sometimes changes as the fishing season goes on. At first, the bears will consume the entire salmon, but as the season goes on, on if it has been a good salmon run, the bruins become more selective, restricting their feeding efforts to the more nutritious bits. They peel off the skin, they nibble out the brains, and tear open the abdomen to gain access to the roe. It is not uncommon to see a grizzly step on a fish, causing a stream of orange, nutritious eggs to spew forth. The bears use their tongue to lap-up the eggs.

References:

Bledsoe, T. 1987. Brown Bear Summer: Life Among Alaska's Giants. New York, New York, E P Dutton. 249 Pp.

Hendry, A. P. and O.K. Berg. 1999. Secondary sexual characters, energy use, senescence, and the cost of reproduction in sockeye salmon. Can. J. Zool. 77:1663-1675.

Quinn, T.P., S.M. Gende, G.T. Ruggerone, and D.E. Rogers. 2003. Density-dependent predation by brown bears (Ursus arctos) on sockeye salmon (Oncorhynchus nerka). Can. J. Aquat. Sci. 60:553-562.

©2008 Scott W. Michael

CLAM-DIGGING BROWN BEARS

A female brown bear nimbly uses her large claws to separate the valves of a razor clam and get to the juicy morsels within. See slide show below for more on this bear. Photo by Scott W. Michael.

When it comes to food, brown bears are very opportunistic. As discussed in past posts, they are also very intelligent. Consequently, they’re always looking for new food sources that they can exploit. Along the coast of Alaska, brown bears congregate in salt marshes in spring and early summer. They feed on sedges, grasses and forbs as they wait for migrating salmon to arrive in nearby estuaries. Some bears move out of the marshes and sedge flats and feed on animals that inhabit shore habitats. Along the Katmai coast, there are large tides that expose an expansive intertidal flat that is exposed for three to five hours a day. Certain bears utilize this habitat, hunting for mussels, isopods, barnacles, marine worms (polychaetes and peanut worms) and small intertidal fishes (blennies and sand lances). While it may seem that burrowing clams would be impervious to brown bear attack, there are some bruins that have learned how to locate, capture and handle these infaunal mollusks.

The intertidal zone along the Katmai coast is home to a handful of clam species. The four species that are known to be eaten by brown bears are the soft-shelled clam (Mya arenaria), the razor clam (Siliqua patula), Nuttall’s cockle (Clinodcardium nuttallii) and the Alaska surf clam (Spisula polynyma). These mollusks spend most of their lives below the sand surface, taking in fresh seawater and planktonic food through tube like siphons. The siphons extends from the clam up to the sand surface. (Those species with a shorter siphon remain near the sand surface in order to respire and feed, while those with a longer siphon can burrow to greater depths.) Many of the burrowing clams are adapted to living in the intertidal zone. When the tide goes out, they remain buried in their wet, sandy sanctuary and await the rising tide to bring back life giving oxygen and food.

The slide show above documents the clamming behavior of a female brown bear, with three spring cubs (the latter are not seen in the slideshow). Photos by Scott W. Michael

Clam-hunting Techniques

At low tide along the Katmai coast, you may see an individual brown bear, or a bruin family (sow a cubs), slowly meandering across the tidal flat with nose skimming the sand surface. Somehow the bears detect the buried clams (possibly by using their keen olfactory senses). When they do, the ursid will stop and begin digging at a leisurely pace. The mollusk-hunting bear will lean on one front paw and use the other as a shovel. It will methodically lift the substrate from the hole and push it back behind the excavation. If the clam is deeper in the sand, the bear might lean on its elbow, laying its head on the foreleg, in order to thrust the digging paw deeper into the substrate. When it reaches the bivalve, it will extract it by lifting it out with its claws/paw or by shoving its head into the hole and grasping the clam in its jaws. Troyer (2005) reports that like fishing, bears vary in their clam-digging prowess. Some bears are very effective “clamers,” while others are inept. If a bear’s digging activity never or rarely results in positive reinforcement, they give up this activity after a time. Troyer also notes that when it comes to clam-digging, some bears are exclusively “right-pawed,” while others only use their left paw.

In a study conducted on Katmai bears, it was found that the average harvest rate for clamming bears was 0.69 ± 0.46 clams per minute (Smith et al. 2004). The percentage of excavations that yielded clams was 63%. When it comes to the number of clams ingested, Troyer (2005) reported seeing individual brown bears dig up as many as 50 to 100 clams in one cycle of the ebb-tide. In one four hour period, I watched a female with cubs dig between 180 to 200 holes (it was impossible to determine how many clams the bear ate during this period).

Once they extract the mollusk from its subterranean refuge, the bear has to get to the meat that is housed within the clam’s calcareous armor. In the case of the soft-shelled and razor clams, the valves (which are the two parts that make-up the shell) are not that hard. A bear’s clam-handling technique can vary from one individual to the next. After pulling a clam from the substrate, some bears nimbly use the claws to pull the valves apart (see slide show below). Some bears place the bivalve on the beach and then stomp on it or roll it under their massive paw. This results in the valves breaking apart, which enables the bruin to extract the meat with their lips and tongue. In the case of soft-shell clams, the bear may take the entire bivalve into its mouth and masticate it. This resulted in their swallowing a considerable amount of shell material as well as the clam flesh (along the Katmai coast it is not unusual to see scat that contains clam shell fragments).

Clams Eaten

Katmai Brown bears do not feed on the various clams species in equal numbers. Smith et al. (2004) found that 77% of the time bears dug-up soft-shelled clams (Mya arenaria), 18% of the time they pulled out razor clams (Siliqua patula) and 2% of the time they excavated other clam species (namely Nuttall’s cockle [Clinodcardium nuttallii] and the Alaska surf clam [Spisula polynyma]). Clam species selection is thought to be more a function of species availability rather than preferences related to a species nutritional value. For example, the bears apparently feed more on the soft-shelled clams because they are found closer to shore and thus are available to foraging bears for longer period of time. There is not a difference in the bear’s harvest rate or success rate between soft-shelled and razor clams, even though the razor clam have what appeared to be a more effective anti-predation strategy – that is, when disturbed they pull themselves deeper into the substrate.

Who Digs Clams?

When it comes to a proclivity to dig clams, there are differences between the sexes. Smith et al. (2004) reported that of 233 clamming bouts observed, less than 1% of the clam-diggers were adult males, 44% were females with cubs and 55% were single bears of undetermined sex. How does the overall population of bears in this area compare with those observed clamming? The researchers found that of 16,738 bear (or bear family groups) encounters (over two years), 13% were large adult males, 8% were females with cubs-of-the-year (spring cubs), 17% were females with dependent young and 62% were single bears. It is obvious that females with cubs are overrepresented on the intertidal flats (44% of total population vs. 25% of bears observed clamming), while adult males are greatly underrepresented (13% vs. 1%). During focal sampling of bears working the intertidal zone (that is, where they followed individual bears and recorded their behavior), large adult males spent 0.1% of their time clamming, while females with dependent young invested 4.7% of their time digging mollusks (the single unsexed bears spent 1.4% of their time). The conclusion: females with young cubs most often feed on clams on the intertidal flats.

Benefits to Clam-digging

So what are the benefits for the bruins that dig clams? First of all, clams are a good source of digestible protein. Those brown bears that supplement their diets with these nutritional mollusks, are able to spend much less time munching on vegetation in order to meet their springtime energy requirements. Smith et al. (2004) predicted that a 160-kg brown bear that consumed razor clams for two hours a day could cut down total foraging time by 27% (compared to bears that only consumed vegetation). There is another advantage for clam-digging females that have cubs in tow. Because adult males are rarely seen on the intertidal flats, females with dependent young can forage in this habitat without exposing their offspring to potentially dangerous males. Less time spent feeding and less dangerous for young ones – a definite twofold advantage to hunting clams.

References

Smith, T.S. and S.T. Partridge. 2004. Dynamics of intertidal foraging by coastal brown bears in southwestern Alaska. Jour. Wildlife Manag. 68(20):233-240.

Troyer, W. Into Brown Bear Country. Univ. Alaska Press, Fairbanks, 130 Pp.

Copyright (2008) Scott W. Michael

GRIZZLY BEAR PREDATION ON MUSKOX

Ovibos moschatus is a formidable beast that is sometimes preyed upon by grizzly bears.Photo Credit:US Fish and Wildlife Service.

The muskox (Ovibos moschatus) is a large ungulate (the average male weight is from 273 to 364 kg [600 to 800 pounds]) equipped with curved horns and a shaggy pelage which can be up to 10 cm (4 inches) thick. It is a close relative of the sheep or goats (subfamily Caprinae) and is able to withstand incredibly frigid, arctic conditions (down to at least – 70 ºF). Muskox tend to live in herds and are famous for their defensive posturing – they often form a defensive circle with their heads (i.e., armament) facing outward toward the potential threat. Youngsters often hide amongst the adults for protection.

The barren-ground grizzly bears and muskox overlap in their distribution in northern Canada and Alaska. This shaggy beast would appear to be fairly impervious to grizzly attack. But, this is not the case. Grizzlies were originally reported feeding on muskox by early explorers and with recent reintroduction of these ungulates in parts of the Arctic, there have been a number of papers written on the predator-prey relationship of U. arctos and O. moschatus. Below I have reviewed what is known about the barren-ground grizzly predation on muskox.

Multiple Hunting Strategy

In the Thelon Game Sanctuary, grizzlies and muskox coexist, but the relationship is not always copasetic. Near the Thelon River, bears may use thick willow stands along the waterway to ambush muskox feeding on sedge in nearby clearings. Willows also attract muskox, as it is a preferred food of this beast. Gunn and Miller (1982) report finding a bear on a freshly killed, bull O. moschatus. They were able to scare the adult bear off and examine its kill and concluded that the bear had dispatched the big ungulate by first grasping its nose (crushing the nasal turbine bones and tearing off the nose in the process) and then inflicting a crippling bite to its skull. By grasping the nose, the bear may have prevented the muskox from bringing its horns to bear and also may have been more effective at throwing the animal to the ground.

In another study carried out in the northeastern Arctic slopes of Alaska, 92 grizzly-muskox interactions were observed (Reynolds et al. 2002). Fifty percent of these were known kills, 40 % were possible kills or scavenging events, and 10 % were incidents where a grizzly was seen chasing muskox. It was estimated that 16-39 % of muskox mortality was the result of bear predation. During the study period (1982-2001) the number of muskox killed by grizzly bears was zero to two deaths per year before 1993, one to four musk ox per year from 1994-1997 and five to ten deaths per year from 1998-2001. This increase in kill numbers was a function of an increase in the size of musk ox herds. An increase in kills may also be indicative of the bears learning how to better attack and take down these big, formidable animals. While solitary adult bears were most often seen attacking muskox (69 occasions), pairs or trios of adult bears were seen chasing, killing or eating these animals (three episodes). Sows with cubs or yearlings were seen interacting with muskox on three occasions.

Surplus Killing

Grizzly bears sometimes engage in surplus killing of muskox. In the study carried out by Reynolds et al. (2002) there were ten episodes where one to three bears killed from two to four adult muskox. On several occasions even more muskox were dispatched during a single hunting bout. For example, in one case five individuals (two adult females, a yearling and unsexed adult musk ox) were incapacitated by a single bear. In another case, a grizzly killed four calves and in another incident the victims were one adult female, one two-year old male and one yearling. In most cases, solitary bears were involved in these killing sprees, but in one case three grizzlies instigated the melee.

Clarkson et al. (1993) reported a fascinating case of surplus killing of muskox calves by a heterosexual pair of adult grizzlies. Within a distance of about two km, the two bears took down five young musk ox. By doing a little forensic work, the researchers were able to put together a likely picture of what had happened. Rather than form a defensive circle to try and parry the bear attacks, this herd of musk ox tried to out run the grizzlies. The researchers postulated that the calves trailed behind the adults and, therefore, were more vulnerable. The two bears chased the herd, which consisted of 40 to 50 muskox (with a minimum of eight calves). They killed the first calf and ate 90 % of the carcass. They then chased the herd down again and about 1.5-2.0 km from the first kill dispatched a second young musk ox. They ate 60 % of this second calve and began the hunt again. They killed the third calf about 300 m from the second. The third calf was about 30 % consumed by the bears and a wolverine (Gulo gulo) that was feeding on the carcass when the researchers arrived on the scene. The fourth calve was killed 400 m from the third. A golden eagle had just begun to feed on calf four when the researchers arrived. The final calf was killed about 200 m from the fourth – this last young muskox was not eaten either.

References:

Clarkson, P. L. and I. Sarma Liepins. 1993. Grizzly bear, Ursus arctos, predation on muskox, Ovibos moschatus, calves near the Horton River, Northwest Territories. Canadian Field Nat. 107:100-102.

Gunn, A. and F. L. Miller. 1982. Muskox bull killed by a barren-ground grizzly bear, Thelon Game Sanctuary, N.W.T. Arctic 35:545-546.

Reynolds, P. E., H. V. Reynolds and R. T. Shideler. 2002. Predation and multiple kills of muskoxen by grizzly bears. Ursus 13:79-84.

Copyright (2008) Scott W. Michael

BIRD FOOD (AVIAN-EATING BEARS)

Puffins on Ninagiak Island - brown bears will swim to the island from the Katmai coast in order to take exploit ground nesting sea birds. Photo by Scott W. Michael.

Birds are not staple fare in most grizzly bear diets. But being the opportunists that they are, these bruins will sometimes feed on the eggs and chicks of ground nesting birds. The first report of bird-eating I could find in the literature comes from a paper on the brown bears of Kamchatka (Bergman 1936). This naturalist reports that Russian U. arctos enter marshy areas before the salmon run to raid the nests of water fowl (i.e., “wild ducks”).

In a more recent reports, grizzlies in the Canadian Arctic Region (Tuktoyaktuk Peninsula) were observed eating the eggs of snow geese (Chen caerulescens) and adult ptarmigan (Lagopus spp.) (the latter is a rare event), while coastal brown bears, along the Katmai coast, have been observed capturing seagulls that were attempting to share a fish meal. In the “lower 48,” Gunther and Renkin (1989) observed Yellowstone grizzlies attempting to capture ducks (Anatidae), Canadian geese (Branta canadensis) and sandhill cranes (Grus canadensis). This occurred on rare occasions and the bears were never seen to successfully capture avian prey. Even so, there is no doubt that they do occasionally capture and eat these birds.

Campbell (1991) found that brown bears invaded the nests of the dusky Canada goose (Branta canadensis occidentalis) on the Copper River Delta, Alaska. About 50 % of the nests in this area succumb to predator activity and subadult and female brown bears with young were implicated in over half of all nests destroyed (males and solitary females rarely enter the nesting area). The bears would enter the nesting areas as soon as the geese began nesting until mid to late summer, at which time they moved to salmon streams.

Brown bears greatly impact the distribution of certain seabirds on the islands along the Katmai coast. Here, U. arctos has been observed swimming relatively long distances to gain access to ground nesting birds. For example, in Hallo Bay, Katmai National Park, brown bears will swim the 3.2 km (2 mi.) to Ninagiak Island to feed on the eggs of glaucous-winged gulls (Larus glaucescens) and puffins (Fratercula corniculata and F. cirrhata). Bailey and Faust (1984) reported the following at another island in the area:

“A sizeable tufted puffin colony…was destroyed by a brown bear. When we visited this island.. only about 100 puffins were milling about the grassy, burrow-ridden headlands, and a bear was systematically excavating burrows around the island’s perimeter. Entire slopes were dug up to the depths of nest chambers, and eggs shells and feathers were common.”

Puffins often nest in colonies. They dig burrows that are usually around 1 to 1.2 m (3 or 4 ft.) deep (there are reports of tufted puffins digging burrows as deep as 2.75 m [9 ft.]). In some areas, like Ninagiak Island, the burrows are dug on hillsides among scattered rocks and boulders. Brown bears use their long claws and massive shoulder muscles to displace rocks and earth in order to penetrate the nesting chamber. Both Alaskan species of puffin lay a single egg that hatches in 42 to 47 days. The chicks fledge for another 45 to 55 days, remaining in the burrow this entire time. While one parent takes care of the egg or chick, the other goes out to fish for food. Eggs and young puffins are available as bear food from at least June to August or September. On islands frequented by bears, puffins are rare.

Gull populations can also be impacted by the presence of coastal brown bears. Bailey and Faust (1984) report that gull nests were often found destroyed by bears and that bruins limit where these bird’s reproduce. They conclude that:

“The ubiquitous bears probably are largely responsible for the fact that fewer seabirds nest between Kamishak and Amber Bays than along any similar length of coastline on the Alaska Peninsula.”

The glaucous-winged gull, which is targeted by brown bears on Ninagiak Island, usually scrapes its nest in the ground and fills it with bits of grass, weed, moss, roots, twigs, turf, seaweed, etc. To give you some idea how profitable gulls can be as a food source for bears, consider this. Glaucous-winged gulls form nesting colonies which can number from 10 to as many as 10,000 pairs. Sometimes other gulls also form part of these large nesting aggregations. From 1 to 3 eggs are laid. They hatch in mid- to late June and are raised within the nesting territory.

During their study, Bailey and Faust (1984) observed 40 brown bears on or swimming between islands. They reported that many of these were sows and their cubs. It is advantageous for a mother bear to take her offspring to one of these offshore islands, not only because of the ready supply of “bird-food,” but also the island is likely to provide a safer refuge away from marauding male conspecifics. It is likely that cubs that were taken to an island by their mother, will return with their out young in time.

References:

Bailey, E. P. and N. H. Faust. 1984. Distribution and abundance of marine birds breeding between Amber and Kamishak Bays, Alaska, with notes on interactions with bears. Western Birds 15:161-174.

Campbell, B. H. 1991. Activities of Brown Bears on the Copper River Delta, Alaska and Their Impact on Nesting Dusky Canada Geese. Northwestern Naturalist, 72:92-99