Calf Production, Calf Survival, and Recruitment of Muskoxen on Banks Island during a Period of Changing Population Density from 1986-99

Abstract

ABSTRACT. Population estimates for muskoxen (Ovibos moschatus) (age > 1 year) on Banks Island increased from 29 168 (SE 2104) in 1985 to a peak of 64 608 (SE 2009) in 1994 and then declined to 45 833 (SE 1938) in 1998. From 1986to 1999, annual sex and age classification surveys of muskoxen were conducted during summer. We estimated calf production (number of calves per 100 females aged 2 years or more), calf survival, and recruitment (number of yearlings per 100 females aged 2 years or more). Calf production ranged from 31.3 to 56.3 and was similar between periods of increasing and decreasing density (mean = 42.3 vs. 40.8). Calf survival ranged from 23% to 83% and was generally higher while density was increasing than during its decline (mean = 60 vs. 45). Survival at a given density was lower following the 1994 peak in density. Recruitment ranged from 10.0 to 41.7 and was higher (p = 0.06) during the period of increasing density than during the decline (mean = 28.0 vs. 17.2). Calf survival and recruitment were lowest following two consecutive severe winters, but animal density explained more of the variation in survival and recruitment than did late-winter snow depth. There was a positive relationship between the proportion of sedge (Carex spp., Eriophorum scheuchzeri) in the summer diet and calf survival and recruitment. Patterns of calf survival and recruitment plotted against density were consistent with those modelling a density-dependent relationship. Our results suggest that severe weather alone cannot explain the fluctuations in the population dynamics of Banks Island muskoxen and that underlying density-dependent responses acting upon calf survival and recruitment offer an alternative explanation. . La survie des veaux et le recrutement étaient les plus faibles après deux hivers rigoureux, mais la densité des animaux expliquait mieux la variation dans la survie et le recrutement que l'épaisseur de la neige à la fin de l'hiver. Il y avait une relation positive entre la proportion de carex (Carex spp, Eriophorum scheuchzeri) dans l'alimentation estivale et la survie des veaux ainsi que le recrutement. Les tendances dans la survie des veaux et le recrutement tracées en fonction de la densité donnaient des courbes en accord avec celles représentant un modèle variant avec la densité. Nos résultats suggèrent que la rigueur du climat ne peut à elle seule expliquer les fluctuations dans la dynamique de la population du boeuf musqué de l'île Banks et que des réactions fondamentales variant avec la densité qui influent sur la survie des veaux et le recrutement offrent une autre explication.

Monitoring nutrition of a large grazer: muskoxen on the Arctic Refuge

“…Reproductive rates of female muskoxen are modulated by body condition [24], such as fat reserves, as well as the dietary supply of energy and trace nutrients [25]. Serum indices of Cu, as well as hepatic concentrations of Cu, were low for female muskoxen during a decline in numbers on Banks Island, Canada [9,17]. Maternal copper can directly affect the growth of the fetus and indirectly affect the survival of young muskoxen because hepatic copper is accumulated in utero and apparently used through the first 60-100 days from birth, when the dietary supply of Cu in milk is low [19].…”

“…Several factors influence the dynamics of muskox populations, including abiotic factors, such as weather and terrain [5,6], and biotic factors, such as predation on young and adult animals [7]. Effects of weather and predation on production, survival and recruitment of young muskoxen [1] can be exacerbated by constraints on food resources that may ultimately dictate the growth and persistence of the population in an area [8,9]. Relatively sedentary populations like muskoxen, which increase rapidly in abundance, may affect forage communities in local areas [10].…”

Northwest passages: conservation genetics of Arctic Island wolves

“…D S between Banks and Victoria Island is less than half the next smallest inter-island distance (Table 3), and so of populations surveyed here, Victoria Island is the most likely origin of post-poisoning Banks Island wolves. The Banks Island muskoxen population has increased to 45,000 over the last two decades (Gunn et al 1991;Larter and Nagy 2001a). Despite concurrent declines in Peary caribou (R. t. pearyi) density (Larter and Nagy 2000), there is no doubt wolves have access to ample prey.…”

Growth in an Arctic Grazer: Effects of Sex and Dietary Nitrogen on Yearling Muskoxen

“…Average fat content of muskoxen at 312 days of age was only 1.4% of body mass, which is similar to that of growing caribou (R. tarandus; 1.4-2.3%- Gerhart et al 1996;Reimers et al 1982) and yearling muskoxen from the wild (7%- Adamczewski et al 1995). Although gains in limb length may benefit mobility in deep snow, the lack of large fat reserves during the 1st winter could contribute to mortality of young muskoxen (Larter and Nagy 2001a). Maternal supplies of energy and nutrients in milk may offset low fat reserves of young muskoxen during the 1st winter because weaning may be delayed until the end of winter (Parker et al 1990;Thing et al 1987).…”

“…Consequently, the availability of plants with higher N concentrations (10-20% CP) such as willow (Salix- Klein andBay 1990, 1994) may complement and supplement the consumption of graminoids (Boyd et al 1996). Forage abundance and diversity may therefore influence survival and recruitment of young muskoxen, especially in regions with high population density (Gaillard et al 1998;Larter and Nagy 2001a).…”