Fauna Series No. 5

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

CHAPTER THREE:
DALL SHEEP (continued)

Do the Wolves Prey Mainly Upon the Weak Sheep? (continued)

SEGREGATION OF SHEEP REMAINS INTO CLASSES

Old Age Class.—An animal definitely past its prime becomes a member of the weaker part of the herd. Therefore, an old-age group can be segregated and placed in the category of weak animals which in this case are doomed to a relatively early death even in the absence of predation.

The oldest ram found was 14 years of age, and there were three of this age. Only one ram was found in the 13-year class, Many rams belonged to the 10-, 11-, and 12-year-old classes. It appears that few rams live beyond 12 years of age. When a ram is 11 or 12 years old, little remains of his teeth. Tooth wear indicates that an 11- or 12-year-old ram has about completed his life span, and animals a year or two younger are probably beginning to fail.

Four females were 12 years old; these were the oldest recorded. The growth rings on a female horn are close together when the animal is old so that a person could make a mistake of a year or so. Consequently what is recorded as a 12-year-old might possibly be a 13-year-old, but, even so, there were still only four in this class. While there are many rams in the 12-year age class, there are very few ewes reaching that age and there also are few ewes in the 11-year age class. These data on longevity strongly suggest that the ewes are shorter lived than the rams. Since few ewes pass the 10-year mark, it appears justifiable to place those 9 years or older in the old-age class. Possibly the old age group for rams should begin at 10 years, but in the interest of uniformity and simplicity they have been classified the same as the ewes. So far as these calculations are concerned, if old age for rams should be construed as beginning at 10 years, the change would not greatly alter the final figures.

Two- to 8-year Class—Animals in Their Prime.—Animals from 2 to 8 years old are placed in one age group. It is thought that such animals are in their prime and are least vulnerable to predation and other factors of the environment.

Lambs and Yearlings.—The young are arbitrarily called lambs until about October, and after that until they are about 15 months old, they are called yearlings. Most yearling skulls are from animals less than a year old, from animals which have died during the winter.

It is difficult to evaluate the vulnerability of the young sheep. Everything indicates that it is probably correct to call them weaker than healthy animals in the 2- to 8-year class. But lambs a few weeks old are not easily captured by wolves, so one would expect that after a few months they would be able to avoid wolves almost as well as the sheep in their prime. Perhaps the young sheep, up until early winter, are not especially vulnerable, although they would be handicapped by inexperience. But as the winter advances and the quality of the food decreases they perhaps become progressively weaker just as the adult sheep become progressively thinner. Because they are still growing they may be more affected by hardship than older animals. Many of course succumb to winter hardship, and apparently the strength of the healthier ones is somewhat reduced so they become less able to avoid the wolf. It is thought that on the average the term weak may be applicable to the yearlings so they have all been so classified in discussing the skull data.

Diseased and Injured Animals.—Actinomycosis: The ungulates in general seem to be subject to certain diseases which cause lesions in the mouth. These lesions may be caused by at least three diseases—actinomycosis, necrotic stomatitis and actinobacillosis. The mortality in necrotic stomatitis is high, while in the other two diseases the infection is often chronic. There is some confusion as to the causative organisms, but actinomycosis and necrotic stomatitis appear to be caused by two species of a ray fungus, respectively known as Actinomyces bovis and Actinomyces necrophorus. Actinobacillosis is caused by another organism of similar appearance called Actinobacillus lignierisi. Tissues in the mouth cavity are invaded by these organisms through abrasions such as are sometimes caused by coarse vegetation or grass awns. The lesions may occur on the tongue, hard palate, cheeks, and near the teeth, especially around the molariform teeth. Actinomycosis is thought to generally affect the bone, and the other two diseases the soft tissues. But there is a possibility that necrotic stomatitis, when chronic, also affects the bones. Much more bacteriological research is needed, especially among game animals, to solve all aspects of the diseases. An affected bone may be eaten away or enlarged and made spongy. If the bone is necrosed near the teeth, which is frequently the case, the latter may drop out or grow at abnormal angles. When a tooth drops out, the one that opposed it usually becomes elongated and sometimes spikelike because it meets no surface or strikes only the side of another tooth. Mandibles affected are sometimes bent or so necrosed that they are almost severed. The mechanical difficulties in the teeth resulting from the disease are frequently considerable, and since mastication is so important to an ungulate, any injury to the teeth becomes a serious handicap.

In Jackson Hole, Wyo., where much work has been done on the diseases of elk, a large percentage of the elk deaths during the winter and spring months are due to necrotic stomatitis (O. J. Murie, 1930). The calves in their first winter are the principal victims, but older animals also succumb. In the acute form of the disease the animals do not last long and die while still in good flesh. In older animals the disease at times seems to take on a chronic form, causing severe necrosis of the bone. Whether more than one disease is present has not been completely worked out, but further bacteriological studies are in progress.

Evidence of what appears to be necrotic stomatitis has been found among wildlife in many localities, and in deer, antelope, moose, caribou, and Rocky Mountain bighorn, as well as in elk. W. Reid Blair (1907) reported finding actinomycosis in a severe stage in three of six skulls of Ovis stonei from the Stikine River country in northern British Columbia.

Figure 42: The upper specimen shows one side of the palate of an 8-year-old ewe partially destroyed by necrosis. The lower specimen shows necrosis and exostosis near the angle of the mandible of an old ewe.

In the Jackson Hole elk herds the disease seems to take a regular toll. Some years it is a little more serious than others and it especially affects the calves. The young are especially susceptible, possibly because their mouths are tender and easily pierced by vegetation and the wounds in the mouth attending changes in the dentition afford a portal of entry. Although usually the incidence of the disease is not high and (according to paleontological evidence) has afflicted the animals for thousands of years, still it is important in the consideration of game losses and should be recognized in order that losses can be better analyzed.

The extensive necrosis and exostosis found in the skulls indicates that many sheep in Mount McKinley National Park are affected by either necrotic stomatitis or actinomycosis. Because of the bone conditions the disease has been referred to as actinomycosis although bacteriological studies would be necessary to determine the organism. Evidence of the disease was found in animals of all ages. Many had undoubtedly recovered but had been left handicapped with misshapen jaws and loose and missing teeth. Some yearling skulls were found which showed strong evidence of the disease. But since it appears that yearlings often die before the bone is affected, especially from necrotic stomatitis, many yearlings afflicted with it would not show evidence of its presence.

Figure 43: Mandibles of a 9-year-old ram. The one on the left, greatly enlarged and porous, shows an extreme diseased condition.

In the present study, animals whose skulls showed severe conditions of necrosis or exostosis were considered weakened by disease. Those with but slight necrosis were considered healthy. Figures 42 to 45 show malformations resulting from necrosis and exostosis.

Some animals affected by these bone changes would be unable to masticate the food well enough or fast enough. Others would have chronic infections in the mouth when the food kept the sores open and irritated. Still others would be ailing with the disease itself. All but six of the diseased sheep listed in Tables 4 to 7 inclusive (pp. 122 and 123) are those showing severe cases of what has been referred to as actinomycosis.

Some notes on domestic sheep are suggestive of the effect of old age and missing teeth, or what is termed a "broken mouth" by sheepmen. O. J. Murie recently discussed the matter with some experienced, successful sheepmen. One of them said that after ewes are 6 years old they do not survive well on the desert in winter even though they have all their teeth. Teeth generally "spread" and fall out after the sixth year and the losses then become heavier. After the ewes are 6 years old they are disposed of or put on a ranch. It was also stated that the sheep probably never exceed 14 years of age. Another sheepman thought that ewes wintered fairly well at 7 years and stated that sometimes he had wintered them on the desert even as old as 9 years. But all of the sheepmen agreed that as soon as a ewe had missing teeth her chances for wintering successfully on the desert dropped considerably.

Figure 44: Lower jaw bones of Dall sheep. The mandible at top shows necrosis on the side of the molars. The mandible below is bent due to necrosis, and a tooth is missing. The side of the molar behind the cavity has become worn, thus making a sharp-pointed tooth.

C. L. Forsling (1924, pp. 20—21), in his studies, has come to similar conclusions concerning the effect of age and tooth deterioration on domestic sheep. He writes: "Ewes should not be kept in the range bands after they are 5 or 6 years of age. Animals that have reached that age are less able to rustle forage than are younger sheep. Furthermore, if such animals are held over, they may not be in condition to mother lambs or survive a critical period. The condition of the teeth usually determines whether or not ewes will do well on range feed. Gummers, or animals with few or irregular teeth, are of doubtful value on the range and should be disposed of." These conclusions correlate tooth deterioration with loss in stamina, suggesting that a similar correlation may exist in mountain sheep.

Severe necrosis may only be present in one mandible or along one tooth row, and the remainder of the tooth rows may appear quite normal. On a few occasions two or three of the tooth rows were picked up, none showing at the most more than slight necrosis, and the presence of severe necrosis was not known until the last tooth row was found. Since a number of skulls are represented by only one or two tooth rows, some cases of severe necrosis were no doubt missed so that the incidence of the disease was probably higher than recorded in Tables 4 to 7 (pp. 122 and 123). Diseases other than actinomycosis cannot be determined from the remains, so that some sheep designated as non-diseased might possibly have been diseased.

Figure 45: Teeth of Dall sheep. The specimen at lower left shows crooked teeth resulting from necrosis and missing molars. The other three tooth rows show an abnormal condition in a 6-year-old ewe. The upper and lower molars should have met on the flat surface. Instead they slid past each other, wearing the sides so that sharp chisel-edges resulted. The white areas on the sides of the teeth indicate wear.

Malformed Teeth: Four animals were found in which there was severe malocclusion of the molariform teeth which seemed not to have been caused by disease. The teeth did not occlude normally, on a flat surface, but slid past each other wearing off the sides of the teeth and forming sharp-edged chisel-shaped tooth rows. As an example, in one case the lower molars were worn on the outer side, and the upper molars on the inner side, resulting in beveled teeth. On one specimen the lower molars slid past the uppers and gouged into the upper gum. Since these animals were undoubtedly greatly handicapped they are listed as diseased.

Lungworm: The lungs of one yearling were examined and were found to contain many adults, larvae, and eggs of a nematode which probably belonged to Protostrongylus or a related form (Goble and Murie, 1942). Further information is not available as to the incidence of lungworm or its effect on the sheep. No animals are listed as being weakened by heavy lungworm infestation.

Injuries: A yearling was found weakened by internal infections apparently resulting from a fall. A 2-year-old died as the result of a snag puncturing the abdominal cavity. These are listed as diseased.

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