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A Ten-Year History of the Demography and
Productivity of an Arctic Wolf Pack

Introduction


Wolves (Canis lupus) are long-lived animals (Mech, 1988a). However, because they are difficult to study (Mech, 1974; 1994), there is little long-term demographic and productivity information about individuals or their packs. An 8-year demographic description of a pack of radio-tagged wolves in the Superior National Forest of Minnesota seems to be the sole record available (Mech and Hertel, 1983) except for general information about certain packs or individuals on Isle Royale, Michigan (Peterson, 1977; Peterson and Page, 1988).

The present study was conducted during summers 1986-1995 on Ellesmere Island, Northwest Territories, Canada (80° N, 86° W). There, wolves prey on arctic hares (Lepus arcticus), muskoxen (Ovibus moschatus), and Peary caribou (Rangifer tarandus pearyi) (Mech 1988b).

During 1986, I habituated a pack of wolves to my presence and reinforced the habituation each summer (Mech, 1988b). The wolf pack frequented the same area each year and generally used the same den (Mech and Packard, 1990) or nearby dens (Mech, 1993) each summer. The habituation allowed me to remain with the wolves each day and observe them regularly from distances as close as one metre. I usually began observing the pack each year between 14 and 28 June when the pups were about 10-25 days old, and ended observations in early August.

Individual wolves were recognized on the basis of gender (from urination posture), behavior toward me, presence or absence of dark-tinged fur on the back, and such individual features as a missing tooth, ear notch, and scars. Although not all of the individuals in the study were recognizable by single definitive features, combinations of characteristics appeared to be definitive.

None of the pups from a given year was individually recognizable as a specific pup or as a specific yearling the following year, but the assumption was made that all apparent yearlings were the pack's pups from the previous year. This assumption was supported by the fact that all such yearlings demonstrated the habituation to me resulting from their habituation as pups the previous year. In three observations involving 10 individual wolves not from the habituated pack, the animals did not demonstrate habituation; instead, they failed to let me approach closely and ran off.

The study pack consisted of 2-8 adults and yearlings each summer, including an alpha pair (Table 1). Besides the alpha pair, five adults ("auxiliaries") were present during 1986 and 1987 and were assumed to be previous offspring of the alpha pair. No auxiliary remained with the pack after 1987 except a male, "Left Shoulder," which became alpha male in 1988. In later years, no auxiliary except each of two females remained with the alpha pair for more than three summers after their birth year (Table 1). "Whitey," one of the female auxiliaries that remained, became the alpha female. "Mom," the other auxiliary, was the breeder from 1986 through 1989, and when post-reproductive, was the only wolf that remained with the pack as a mature non-alpha animal. This implies that the other auxiliaries dispersed, similarly to wolves elsewhere (Fritts and Mech, 1981; Van Ballenberghe, 1983; Peterson et al., 1984; Messier, 1985; Fuller, 1989; Gese and Mech, 1991).

Table 1.  Tenures of individual wolves of the study pack on Ellesmere Island, N.W.T. during summer.
Pack Members Sex 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995
Mom F  X1 X X X X X - - - -
Alpha Male M X X - - - - - - - -
Left Shoulder M X X X X X X X X X X
Mid Back F X X - - - - - - - -
Lone Ranger M X X - - - - - - - -
Shaggy F X X - - - - - - - -
Scruffy ? X X - - - - - - - -
Whitey F - -2 X X X X X X X X
Grey Back M - -2 X X - - - - - -
Scar Nose M - - -2 X - - - - - -
Little Girl F - - -2 X - - - - - -
No Name M - - -2 X - - - - - -
No Name M - - -2 X - - - - - -
Explorer F - - - - - - -2 X X -
White Faces F - - - - - - -2 X - -
Grey Back II M - - - - - - -2 X X X
Total Adults   7 7 4 8 3 3 2 5 4 3
1 Underlining indicates breeder for that year.
2 Present as a pup but not yet individually recognizable.

In 1988, none of the 1986 or 1987 auxiliaries was present, but two other individuals, Whitey and "Gray Back" accompanied the alpha pair. They were assumed to be pups of the previous year because they were habituated, Whitey and Gray Back were also present in 1989, along with the alpha pair and the four 1988 pups.

When I arrived each year, the study pack was tending pups in the same "traditional" den during 5 of the 8 years they had pups; in 1990, it moved its only pup there from a pit den 2.8 km away, and in 1991 it used dens within 2.8 km of the traditional den (Mech, 1993). During 1989, the pack denned 24 km from the traditional den, but this was the first year after a photographer had crawled into the traditional den and filmed the pups.

During the two summers when the pack was not tending pups when I arrived, the appearance of the abdomen of the alpha female indicated that she had not nursed pups. Furthermore, during 1993 there was no fresh digging at the traditional den or at any of the alternate or subsidiary dens nearby. Thus the pack probably had not produced pups that year. In 1995, there was fresh digging but no pups.

Two females produced pups during the study: Mom and her daughter Whitey. Mom produced four to six pups each year from 1986 through 1989 (Table 2). Of Mom's pups, only the 1988 litter of four could be sexed (by urination posture), and the ratio was three males to one female. All of Mom's pups observed each year in early summer survived at least through early August. Her 1988 litter of four survived at least through August 1989.

Table 2.  Wolf pup production and survival for wolf pack studied on Ellesmere Island, N.W.T.
Year Pups Produced1 Survival Time2
Males Females ?
1986 6 ≥ 3 mo
1987 5 1M ≥ 2 mo; 1F ≥ 8 yr
1988 3 1 0 ≥ 2 mo
1989 4 ≥ 10 mo
1990 1 0 0 6 mo
1991 2 0 0 ≥ 2 mo
1992 1 2 0 1F ≥ 17 mo; 1F ≥ 27 mo; 1M ≥ 37 mo
1993 0 0 0
1994 1 0 0 ≥ 5 mo
1995 0 0 0
1 Produced by Mom during 1986-1989 and by Whitey during 1990-1995.
2 Survival beyond August each year determined through observations of government weather station personnel.

Mom remained with the pack in 1990 and 1991 but produced no pups after 1989. Assuming that in 1986 Mom was at least 3 years old (the age at which Whitey began producing pups) and probably more like 5 years old judging from her general appearance and behavior, she must have been seven to nine years old when she stopped reproducing, and she could have been much older. Reproductive ability in wild wolves appears to extend through about 11 years of age (Mech, 1988a).

Whitey was born to Mom in 1987 and was first distinguishable as a yearling because of her pure white coat which no adult female in 1986 or 1987 possessed. After replacing Mom as the breeder in 1990 at age 3, she produced a single male pup during her first year, two males the next year, two females and a male the following year, none the fourth year, and a single male again during her fifth year, and no pup during her sixth year (Table 2). All survived through early August of their first year, but only the 1992 litter of three survived through their entire first year (Table 2); the 1994 pup survived at least through October 1994.

Mom helped care for Whitey's pups during 1990 and 1991 but was not seen after that. Whitey had dominated Mom during summer 1989 as evidenced by her dominant posture, her behavior towards Mom, and her raised-leg urination. Whitey continued to dominate Mom in summer 1990 and 1991 when Whitey produced the pups. In 1990, when I arrived and Whitey's single pup was estimated at 10 days old, Mom and Whitey both attended the den.

However, on the day I arrived in 1991, when Whitey's two pups were estimated at 10-14 days old, I did not see Mom. Nevertheless, when the pups were about 17 days old on 19 June, Whitey and the alpha male chased a third wolf that could have been Mom from around the den for a distance of at least 2 km. The next day, Mom was seen lying 50 m from Whitey and the pups. Although Whitey thoroughly dominated and chased Mom several times during the next few days, by 24 June, Mom had reintegrated into the pack. During the rest of the summer, her behavior was similar to that of a regular pack member: she attended the pups and accompanying the alpha pair on hunting trips and when the pair moved the pups.

The pack had two consecutive alpha males during the ten-year study period, "Alpha Male" in 1986 and 1987, and Left Shoulder from 1988 through 1995. Left Shoulder was believed to be one of the 1986 pack members judged to be 2 years old at that time. This animal in 1986 had a wound behind his left shoulder blade about 10 cm in diameter (Mech, 1988b). In 1987, the scar was still apparent through the fur. In 1988, Alpha Male, who had a lower incisor missing, was absent, and I and another worker who had observed the wolves in 1986 and 1987 independently judged that the alpha male in 1988 was Left Shoulder.

The origin of Left Shoulder is unknown, but if he was the offspring of Mom and Alpha Male, Whitey would have been his younger sister. Thus his mating from 1988 through 1994 with Whitey would have constituted inbreeding. If Left Shoulder was at least 2 years old in 1986, then he was at least 4 years old when assuming the alpha male role in 1988 and at least 11 years old in 1995. Nevertheless, in 1995 his canine teeth still appeared quite sharp.


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