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Lack of Reproduction in Muskoxen and
Arctic Hares caused by Early Winter?

Results


During most years, muskoxen and arctic hares and their young were seen regularly each summer (Table 1). During summer 1998, however, I observed only 30 muskoxen, in herds of 3,3,7,7, and 10. Most of these herds were seen in the Eastwind Lake area from the west side of Blacktop Mountain, where in previous years up to 151 muskoxen had been counted. In 1998, the herds contained no calves.

Similarly, fewer arctic hares were seen in 1998 than in any previous summer, and not one leveret (young hare) was observed, even when my colleague and I were following a pair of wolves hunting leverets. In 1996, in contrast, I had watched a single wolf kill six leverets in one night. During every other summer except 1990, leverets were common (Table 1). I also interviewed personnel from a weather station and a military base at Eureka and a scientist who had been on foot in the area for several weeks in 1997 and 1998. Although all had seen leverets in 1997, none had observed any in 1998.

TABLE 1.  Records of muskoxen and arctic hares observed during summers (1986-98) in the Eureka area of the Fosheim Peninsula, Ellesmere Island, Nunavut, Canada.
Year Dates Muskox
Calves
1
Arctic Hare
Leverets
1
Remarks2
1986 4 July - 1 August x x 131 muskoxen seen from W side of Blacktop Mt. in one day
1987 23 June - 10 August x x  
1988 20 June - 4 August x x "16 young hares in one group"
1989 14 June - 10 August x x 151 muskoxen and 200+ hares seen from W side of Blacktop Mt. in one day
1990 21 June - 9 August x 0 "very few muskoxen this year;" "no young hares seen"
1991 13 June - 8 August ? x  
1992 2 July - 6 August x x 9 leverets seen in one group; muskox herds of up to 17 seen
1993 1 July - 6 August x x herd of 29 hares; many leverets everywhere
1994 30 June - 26 July x x "many leverets seen"
1995 29 June - 7 July ? ?  
1996 25 June - 1 August x x "'cloud' of 16 leverets;" "muskoxen seen daily everywhere"
1997 2 - 6 July x x "many adult hares and leverets;" "several small herds of muskoxen, some with calves"
1998 1 - 12 July 0 0 herds of 3, 3, 7, 7, and 10 muskoxen seen
1 x = present; 0 = absent (none seen despite extensive travel over long period); ? = travel too localized or too short to be certain.
2 Quoted material is verbatim from field notes.

The third difference between my 1998 prey observations and those of previous years was that in 1998 we found the remains of nine muskoxen that had died over winter. All had hollow long bones with no indication of fat, and only a few had been fed on by wolves. Two such remains were the most I had found in any previous summer. In addition, in July 1998 we watched two wolves kill an old cow muskox and found that the marrow fat in its femur was mostly depleted (Mech and Adams, 1999). During the summers of 1986, 1987, 1989, 1992 and 1994, I had found fresh wolf-killed muskoxen, but their femur marrow had been fully fat.

Unusually severe weather conditions might cause nutritional stress (Thomas et al., 1981; Gunn et al., 1989). But conditions for most of the previous fall, winter, and spring had fallen within long-term norms: that is, daily mean temperatures, monthly precipitation, monthly snowfall, and month-end snow cover for October 1997 through April 1998 were all within the norms for the study area or, for a few months, more favorable. No abnormally deep snow or snow crusts were recorded (Environment Canada, 1998).

However, winter weather began especially early. August and September 1997 were wetter and colder than long-term norms (Table 2). They were also wetter and colder than in 1996, after which reproduction in both muskoxen and hares was recorded in summer 1997 (Tables 1 and 2). Usually temperatures do not remain below freezing until about 5 September, and there is not more than 6 cm of snow cover until October; however, in 1997, temperatures remained below freezing or only slightly above after 17 August, and there was as much as 9 cm of snow cover by 27 August (Environment Canada, 1998). (Although 9 cm of snow is not deep, the wind distributes the snow in drifts that are much deeper in lowlands, where much of the vegetation grows.)

TABLE 2.  Weather parameters in study area during months preceding winter 1997-981 compared to long-term norms and to the same months preceding winter 1996-97 (Environment Canada, 1998).
Month Daily Mean Temperature (C) Monthly Precipitation (mm) Monthly Snowfall (cm) Month-end Snow Cover (cm)
1997 Normal2 1996 1997 Normal2 1996 1997 Normal3 1996 1997 Normal3 1996
August 0.7 2.9 1.0 25.6 11.8 7.7 12.6 4.0 11.6 4.0 0.0 trace
September -10.4 -8.3 -9.0 15.6 9.7 15.0 23.4 10.9 19.2 13.0 6.0 8.0
1 During October 1997 through April 1998, these parameters were normal or more favorable.
2 1961-90.
3 1947-90.


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