Fauna Series No. 5

Fauna of the National Parks — No. 5 The Wolves of Mount McKinley

CHAPTER SIX:
GRIZZLY BEAR (continued)

Food Habits

THE GRIZZLY AS A VEGETARIAN

The grizzly is for the most part a vegetarian, but by necessity rather than choice. There would be more meat in the diet if he were able to get it, as no opportunities to feed on meat are overlooked. Carrion is always relished but is largely obtained fortuitously. Mice are sometimes eaten as tidbits, but they are too small to be relied upon for bulk unless they are very plentiful. Ground squirrels are sought to a certain extent at all times, but this food involves laborious digging, and even then, after much excavation, the squirrel often escapes. At long intervals a marmot is captured.

During the span of about 6-1/2 months that the grizzlies are active in Mount McKinley National Park, their feeding habits pass through three marked phases. In the spring, up to early June, the chief food consists of roots. Then during June and July they feed mainly on green vegetation, chiefly grass (Calamagrostis langsdorfi) and horsetail (Equisetum arvense). In late July when berries become available, and during August, September, and October, the bulk of the food consists of berries.

Roots also become part of the late fall diet. These principal foods are supplemented by others. A few ground squirrels are caught and eaten at all seasons, and carrion is always highly acceptable.

The data on bear food habits were obtained during 3 years, and as the general pattern was the same each year it seems that the data presented depict the normal diet of the grizzlies. A total of 201 bear scats were analyzed in detail. Many others examined cursorily in the field corroborated the data obtained from those studied minutely and listed in Table 17. The data secured from watching bears feeding were more extensive than those secured from the examination of scats and were highly important in corroborating the scat data and rounding out the entire food-habits picture.

The data from the droppings are segregated according to the periods in which the different food habits prevail, for to combine the data for the different periods would fail to show the shifts in food habits. Most of the droppings were accurately dated.

TABLE 17.— Results of food analyses of 201 grizzly scat s collected in Mount McKinley National Park in 1939, 1940, and 1941 [1]

ANNOTATED LIST OF GRIZZLY FOODS

Roots.—Six of the 25 scats, gathered in May, contained roots of Hedysarum. Many observations of the bears during May, however, indicate that this ratio does not give a true picture of the diet during this period. Of course, the number of scats are too small for a good statistical figure, but aside from that there are other reasons for the small proportion containing roots. The scats containing grass were from the previous year. The number of scats containing sheep is not representative because I spent much of my time searching for sheep remains and covered rather thoroughly the area where bears had fed on sheep. I would estimate that normally, during May at least, 75 percent of the food of the bears consists of roots.

Throughout May and into the first week of June the majority of the bears seen were digging for roots. Generally they seek the roots on the vegetation-covered bars or low slopes but at times they also seek roots far up on the mountains. Some of the favored spots, covering a few acres, had been dug so extensively that they suggested a plowed field. In some of these places bears were seen digging for roots day after day. I was interested in finding much sod turned over by bears just above some cliffs where the sod terminated. It apparently was easy to turn over the sod here where it lay like a carpet with an edge exposed. The bears' activity here had increased the erosion process.

Although roots are eaten mainly in the spring, I also found a number of places where they had been dug during September. Feeding on roots is probably resumed at this time because some of the other foods are either less available or less palatable.

It is difficult to identify the roots found in the scats and often it is not easy to determine the species of plant eaten at the diggings. One of the most sought plants is Hedysarum, including at least, H. americanum and H. mackenzi. It seemed to be the main plant sought in spring and fall. Dixon (1938, p. 145) mentions that Anemone roots were eaten. Former Ranger Harold Herning said he had found roots of dwarf birch eaten. Sheldon (1930) shot five bears during May and the stomachs of all of them were full of "pea vine" roots. There are two or three genera that he might have been referring to, but it is more than likely that it was Hedysarum.

To get at the roots the bear usually places both paws on the ground and thrusts back with the body until a chunk of sod is loosened. This is turned over, the free roots are devoured, and then, with a paw working slowly and lightly, more of the tender roots are uncovered and eaten. I have watched bears feeding in this manner for several hours at a time. The fleshy roots consumed range up to a half inch or more in diameter, and resemble dandelion roots.

Grass.—Grass was found in 92 of the 115 scats picked up in June and July. The average amount of grass in these scats was 75 percent. According to these data 60 percent of the food of the bears during June and July consists of grass and this combined with Equisetum makes up 73 percent of the food of the bears during this period. If it were not for the fact that some roots are eaten in early June and a considerable number of berries in late July when the berries begin to ripen, the percentage of grass in the scats would be even higher. There is a period of about 6 weeks (last 3 weeks in June and first 3 weeks in July) when grass and Equisetum probably make up more than 90 percent of the food consumed.

Many times I examined areas where bears had fed to determine what they had eaten. Only one species of grass, Calamagrostis langsdorfi, was found eaten, except that once a little sedge was also taken. In one scat I identified the seed bead of blue grass and no doubt other grasses are at times consumed. But Calamagrostis langsdorfi, a tall juicy grass, is the species usually preferred. It is plentiful, as is also Calamagrostis canadensis which was not found eaten. In feeding on grass the bears graze steadily, like an ungulate.

Observations made of bears that were feeding substantiates fully the data obtained from the examination of the droppings, namely that during most of June and July grass is the main food of the grizzlies. Palmer (1941) reports grizzlies in the Mount Hayes region feeding on the flowers of Dryas, pods of alpine oxytrope, and willow, as well as on grasses and horsetail.

Horsetail.—Twenty-six of one hundred and fifteen scats gathered in June and July contained Equisetum arvense, and the average amount present in these scats was 57 percent which indicates that large quantities of it are eaten when a patch is found. Equisetum is probably eaten as soon as it becomes available. It is also relished by mountain sheep and caribou. In August the place of Equisetum and grass in the diet is largely taken by berries.

Blueberry—Blueberries (Vaccinium uliginosum) are widely distributed over the park. Some years the crop is better than in others, but it seems that each year there is a generous supply. The new crop of blueberries becomes available in late July, at which time feeding on them begins. One dropping, containing mainly blueberry, was found as early as July 12. During August, September, and early October, blueberries appear to be the most important single item in the diet. During August and September, 41 of 61 scats gathered contained blueberries, and the average amount in each was 60 percent. In this period, according to the data from the scats, they made up 40 percent of the bears' food. Nine droppings, containing an average of 68 percent blueberries, were gathered in July. Some blueberries of the previous year's crop are eaten in May. Three fresh droppings gathered in early May contained mainly blue berries. At this time most, if not all, of the blueberries have fallen to the ground.

Blueberries and other berries are grazed with great vigor. Berries, leaves, and twigs are all gobbled up together. The bears have too much eating to do to be finicky and selective in their berry eating. Even with their roughshod methods they are kept rather busy filling their paunches; furthermore, the food passes through them rapidly, judging from the slight digestion it seems to receive and the frequency with which scats are deposited. On one occasion I saw a bear leave four scats behind her during a single hour.

On August 1, 1940, part of a day was spent watching a mother and her cub feeding on blueberries. She fed continuously and hungrily from 9 a. m., when I first saw her, until 11 a. m. She lay down for half an hour, then fed steadily from 11:30 a. m. until 4 p. m. She lay down for 20 minutes and then commenced to feed. But in a half hour she lay down again and I left her. The cub picked at the berries only part of the time, and frequently rested while the mother fed.

Charles Sheldon, who hunted bears in the McKinley region in 1906, 1907, and 1908, and Joseph Dixon, who spent the summers of 1926 and 1932 in the park, agreed that grizzlies did not eat many berries. Sheldon (1930, p. 117) writes: "It is perfectly clear that many bears of this region do not go for salmon that ascend the rivers, nor do they feed much, if at all, on berries." Dixon (1938, p. 147) quotes Sheldon's statement and observes: "While black bears are notoriously fond of berries the grizzly does not appear to eat them to any great extent. In 1932, 1 found excellent blueberries growing abundantly in the region. However, only a very small proportion of the bear droppings which I examined showed that berries had been eaten."

In view of these statements about the bears in Mount McKinley National Park it may be well to summarize briefly my findings in this respect because they differ so strikingly from the conclusions of Sheldon and Dixon. According to the data from the scats, the five species of berries eaten by the bears made up 68 percent of their food supply during August, September, and October and formed an important part of their food in late July as well. A few berries were eaten in the spring. The berry eating was apparently as extensive in 1940 as in 1939, and although in 1941 I left the park soon after the beginning of the berry season, the bears were observed shifting their diet to berries as in the two previous years. My observations were made from Savage River to Wonder Lake so that the data are fully representative, and the many field observations were in full agreement with the data from the scats. Palmer (1941) found the grizzlies in the Mount Hayes area feeding in spring on berries of the previous season's crop.

Sheldon's conclusions seem to have been made from the stomach contents of 10 bears which he collected. Five of these bears were killed in May and the stomachs, as would be expected, contained mainly "pea vine roots" (probably (Hedysarum). Along with the roots one stomach contained a few mice; one, a ground squirrel; one, 2 mice; one, 1 mouse. Three bears—a mother and two cubs—were shot on August 24 after they had gorged on a sheep, so would be expected to have dined only on meat. A bear killed August 22 had three ground squirrels in its stomach, and the stomach of one killed August 5 contained grass, three ground squirrels, and a shrew. Only the two stomachs from the last two bears would be expected to contain berries. Data from two stomachs is inadequate for drawing general conclusions. Many of the scats examined by Mr. Dixon, which gave him the impression that few berries were eaten by bears, were no doubt deposited during the grass-eating period.

Buffaloberry.—Buffaloberry (Shepherdia canadensis) was found in 28 scats gathered in August, September, and October and made up, on the average, 23 percent of the contents. In July it made up 40 percent of the contents of five scats. On July 18, 1940, a mother bear and cub were observed feeding for about an hour on the berries. Most of them in this particular patch were ripe. In 1939 there was a bumper crop and bears were many times observed eating them. In feeding, the paw is sometimes used to lift the branches so the berries can be more easily eaten. This species is commonly found growing in the rocks and gravel along bars and creeks.

Arctous.—There are two species of Arctous (A. alpina and A. rubra) one having a red berry and generally growing in the woods, and the other a black berry, generally found on open, dry ridges. The latter seems most abundant. I do not know if the bear has any preference.

Arctous was found in 35 scats gathered in August, September, and October and averaged 16 percent of the contents in these scats. Seven July scats contained an average of 21 percent Arctous. It was found in two fresh scats collected in May. The shriveled berries remain attached to the dried stem over the winter.

Crowberry. Crowberry (Empetrum nigrum) was found in 22 scats gathered in August, September, and October, in 2 collected in July and in 1 collected in May. Is is as times eaten in large quantities. Once in an area where crowberries and blueberries were both abundant, a bear fed mainly on crowberries.

Lowbush Cranberry.—Lowbush cranberry (Vaccinium vitis-idaea) is abundant on the slopes and produces heavy yields but it does not seem to be eaten to the extent other berries are consumed. Nine scats found in August, September, and October contained cranberry, averaging a content of 10 percent. One of the scats contained 85 percent cranberry, which shows it may be eaten in large quantities. In June and July, 4 scats contained cranberry. One was a fresh scat gathered in June and the berries in it were from the previous year. On June 12, 1941, a bear fed for a considerable time on cranberries of the preceding year's crop. Because cranberries survive the winter in fairly good condition, it is probable that they are eaten frequently in the spring.

Sorrel.—Sorrel (Oxyria digyna) was noted in only one scat, but since it disintegrates considerably in the digestive tract, traces of it in other scats may sometimes have been missed. On two occasions bears were observed feeding on sorrel. Once a large patch of it had been grazed.

Boykinia.—Small amounts of Boykinia were found in two scats. On July 15, 1939, for a period of 2 hours a grizzly was observed eating large quantities of Boykinia. The stems, leaves, and flowers were all consumed. It also ate much Equisetum later in the day. In feeding, the jaws were opened wide each time a mouthful was taken, and they worked steadily, chopping at the vegetation. There seemed to be an excessive amount of jaw action to accomplish the hurried mastication. This was the only time a bear was observed feeding on Boykinia. However, it is not as widely distributed as most of the food species, so usually it was not available where bears were seen feeding. On one occasion a bear was seen grazing on Calamagrostis langsdorfi and sorrel, and to pass up Boykinia.

Cow Parsnip.—The cow parsnip (Heracleum lanatum) was found eaten on July 15, 1939.

Angelica.—On June 10, 1940, a bear was surprised as he was eating a stem of Angelica genuflexa which had made about half its growth.

Dwarf Arctic Birch.—A trace was found in one scat. On May 28, 1941, a grizzly was observed feeding for a few minutes on the new leaves of dwarf birch, even though a portion of a calf caribou carcass was still available.

Saxifrage.—A trace of the basal leaves of what was apparently Saxifraga tricuspidata was found in two scats. Traces of this plans were also found in some sheep stomachs, so it is apparently a generally palatable species.

Spruce Cones.—Spruce cones, together with dirt and debris, were present in a scat found in May.

Sage.—A trace of sage (Artemisia hookeriana) was found in one scat gathered in September.

Willow.—On May 4, 1940, a yearling was observed feeding on willow catkins. In the Mount Hayes region L. J. Palmer (1941) found willow eaten in June.

Ground Squirrel.—Ground squirrels are eaten as all times. This is the one animal, aside from mice, which the bear can hunt methodically with some success. The spring, summer, and fall diets are all supplemented with ground squirrels, but usually in small amounts.

Although grizzlies are often seen digging out and eating many ground squirrels, other foods make up the bulk of the diet. In May, 4 out of 25 scats contained ground squirrels, in June and July, 10 out of 115 scats contained them, and in August, September, and October they were found in 13 of the 61 scats gathered. According to the data secured from the analysis of the scats, 16 percent of the bears' diet in May consists of ground squirrels, 2 percent in the June and July period, and 3 percent in the August-September-October period. These low percentages are consistent enough to show that ground squirrels actually make up a small but probably important part of the diet.

Much time and energy is generally used in seeking squirrels. Sometimes luck is with the bear, and ground squirrels may be captured in two or three successive excavations, but more frequently a bear may dig out or prospect two or three holes without success.

On August 8, 1939, I came upon a mother bear who had dug a trench 15 feet long and was still digging near the middle of it. Her three cubs were digging in various parts of the trench, perhaps in imitation. In typical fashion the mother would place both front paws on the sod and push downward until the piece gave way. Dirt was pawed out and frequent sniffs taken at the mouth of the hole where she was working. Once she reached into the hole with her arm, lying down on her side so she could reach in farther. At this point the cubs all crowded close in expectation. The mother then moved to another entrance above where she had worked and as she was pressing down the sod with her front paws to loosen it, the ground squirrel scurried forth from the hole. The bear jumped for it but it dodged to one side and managed to escape from four pounces, the last time leaving the bear flat-footed off to one side. But with the next pounce the squirrel was captured. The cubs sat close by watching the mother chew the squirrel but she made no offer to share it with them. One cub did get a morsel which dropped from her jaws. More than half an hour was expended in catching this squirrel.

On July 21, 1940, a grizzly discovered a squirrel under a large snow drift perhaps 25 feet across. There was an entrance on the upper edge of the drift and one on the lower side. The bear kept going back and forth from one entrance to the other. In going from the upper hole to the lower one he often slid down the drift. He would poke his head into the upper entrance to sniff the squirrel, then return to the lower hole to continue digging into the snow. He dug into the drift so far that he was completely hidden. Once while the bear was in the lower hole digging, the squirrel came out through the upper hole, sat up straight to look around, then scurried away from the drift. The bear made a few more trips up and down the drift after this, then lost interest, seeming to realize that the squirrel was no longer there. He stood on the drift hesitatingly, appearing, to me, to be deeply disappointed. A whole half hour of strenuous work, all for naught! He walked off to a patch of grass and grazed, a meal perhaps not as tasty but one more certain.

On October 9, 1940, I saw a female bear wandering over a snowy slope examining a half dozen ground squirrel burrows with her nose. Finally she poked her nose through the snow into the entrance of the burrow and sniffed hard. One could tell by her actions that the scent was hot. She tore away some sod and dug down through the dirt. It took her only a few minutes to reach the squirrel nest, out of which she removed a ground squirrel already in hibernation 20 inches below the surface. Only the upper 2 inches of the ground was frozen at the time. Her cub sniffed about while the mother chewed, and did some digging of its own in the loose dirt pawed up by the mother. The mother examined another squirrel hole, dug into it a little, then wandered off to feed on blueberries.

On August 4, 1941, what appeared to be a lean bear hurried up the slope of a basin, then turned and followed a contour line in search of ground squirrels. It investigated a number of burrows with its nose as it hurried along, intent, it seemed, on finding a squirrel at home. Once it broke into a gallop but stopped abruptly at some holes and began to dig. At first it dug with one paw, at the same time keeping a watch on other holes where the squirrel might emerge. The dens usually have several entrances, and the bear is aware that the squirrels may escape by any of them. Later, both forepaws were used in digging but the bear stopped at intervals to look around for the squirrel. After much digging with no success it moved on, again breaking into a gallop. It stopped at another burrow, where it made a large excavation, still with no success. A magpie sat on a willow nearby watching it dig, waiting for scraps. The bear wandered away from this failure and fed on blueberries which on this particular slope were not abundant that year. This bear had spent about 45 minutes seeking squirrels with no success. It could not afford to gamble further on the ground squirrel hunting so returned to the staple diet. After filling up on berries the bear would probably again try its luck and dig after ground squirrels for it seemed hungry for a taste of meat.

These incidents show somewhat the nature of ground squirrel hunting. If there was not considerable uncertainty in this hunting the bears would no doubt devote more time to it. But there is a limit to the amount of gambling they can indulge in, and even if successful they must return to foods which are available in quantity so fill their rapidly emptying paunches. The ground squirrel has been referred to as the staff of life of the grizzly, but it is only a "side dish."

Hoary Marmot.—Marmot remains were found in only one scat. As a rule, marmots have their burrows among rocks where they cannot be dug out by other animals. Bears travel slowly and are large and easily seen, so perhaps they seldom surprise marmots away from safe retreats. The capture of a marmot is no doubt accidental.

Mouse.—Mouse remains were found in only one dropping. Mice are picked up when available but are too small to be hunted with profit unless very abundant. In years when mice are plentiful they probably are frequently eaten. Sheldon (1930, p. 170—171) found a bear catching mice in the snow on October 9, 1907, at a time when mice were unusually plentiful. He describes its actions as follows: "The bear, evidently scenting a mouse in a tunnel, would plunge its nose into the snow, its snout ploughing through, often as far as 10 feet, until the mouse had gone down into its hole in the ground; then the bear would dig it out and catch it with a paw." In the summer of 1939 mice were scarce, and the following two summers they were present in only moderate numbers. They had been unusually numerous in the fall of 1938 but had died off the following winter. On July 7, 1941, I saw a bear pouncing in a grassy swale, apparently catching mice, the only time a bear was seen engaged in this activity.

Porcupine..—Porcupines are probably not often eaten by bears. However, two porcupine quills were found stuck in a bear's nose, which indicated a too close approach.

Caribou.—Adult caribou are eaten when found as carrion. Six carcasses were seen which had been eaten by bears. Two of these were untouched and putrid when first found by me and were later cleaned up by bears.

A grizzly would be unable to catch a healthy caribou unless he came upon one in an unusually deep sleep, or had some other special advantage.

Caribou calves form a part of the grizzly diet during the calving period. Grizzlies which happen to be ranging where the caribou have their calves no doubt kill some of them, and pick up others which are found as carrion. After the first few days the calves probably are able to escape the bears. In 1941 three different bears were noted on the calving grounds near Sanctuary River feeding on calves. On May 28, 1941, two bears were seen feeding on calf caribou remains, and another lone bear was surprised at a carcass of which only the legs remained. It galloped away and when again seen it was carrying the carcass of another calf. This was carried into a swale where the bear fed on it while keeping a close watch for me. Later in the season, especially in 1940, bears fed on caribou calves which wolves had killed. There did not seem to be any general movement of bears to the calving grounds.

In Table 17 (p. 192) no calf remains are tabulated for May. However, in both 1940 and 1941 some of the bears were eating calves during that month. Probably some of the scats, containing calf, recorded for June and July, were deposited in May. In May 1939, calves were not available to the bears in the eastern part of the park since the caribou calved at the McKinley bar region and westward.

Dall Sheep.—The Dall sheep eaten almost certainly represent carrion. Most of this consists of winter kills and remains of sheep killed by wolves. Sheep make up a smaller part of the food of the bears than the food table indicates because, as already stated, in searching for sheep carcasses, I covered the area well where most bear droppings containing sheep were likely to he found. If the wolves fail to crunch the bones surrounding the brain cavity of a sheep skull, the grizzlies come along later and chew up the skull to eat the brains. On two occasions in the fall when wolves killed sheep, a grizzly was on hand soon after and helped eat the carcass. In one case the bear buried parts of three sheep after feeding on them.

Lamb remains were found in one dropping. This food was probably picked up as carrion. Lambs can avoid bears soon after birth so are probably rarely captured unless diseased. Perhaps more lamb would be eaten as carrion if it were not for the fact that eagles, wolves, and foxes are also on the lookout for it, and there is so little meat in a lamb that whatever animal finds the carrion disposes of it before any others appear.

Ptarmigan.—Remains were found in one scat. Ptarmigan and other birds are picked up as carrion or possibly captured sometimes in a nestling stage.

Wasp.—Parts of three wasps were found in one scat. Bears in Jackson Hole, Wyo., frequently dig out wasp nests that are in the ground, probably chiefly for the larvae.

Garbage.—Grizzlies quickly learn to frequent garbage pits. In 1941 a female with cubs formed the habit of visiting the hotel garbage pit; an other bear visited various outlying camps in the park; and a female with three yearlings visited a road camp garbage pit regularly. Arrangements should be made as soon as possible to dispose of garbage so that it will not be available to bears. Obviously, bears lose much of their attractiveness when spoiled by garbage eating. They also become a destructive nuisance to camps and a source of danger to visitors. In a great wilderness area such as Mount McKinley National Park it seems especially incongruous to see grizzlies feeding on garbage.

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Last Modified: Thurs, Dec 20 2001 10:00:00 pm PDT
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