Report 161

161. McLean B.D., and A. Gunn.  2005. Age and Sex Composition Survey of Banks Island Muskoxen, July - August, 1986. 30pp

ABSTRACT

We classified 3891 muskoxen Ovibos moschatus into age and sex classes on Banks Island from 24 July to 1 August 1986. A Bell 206B helicopter was used to land near large groups (>6) while small groups (<6) were classified from the air. Calves accounted for 14 percent of the all island sample. The calf/cow ratio for the island sample was 37/100 (+1.0 SE) for cows 3 years of age and older. Yearlings were 12 percent of the total or 33/100 (+1.1 SE) cows. The adult sex ratio was 78 males/100 females 3yrs of age and older overall, but only 52 +1.6 (SE) males/100 cows in mixed groups. There were 260 bulls in all male groups and 106 single bulls were observed. The mean group size excluding single animals was 8.14 (+ 5.87 SD). Proportions of calves and yearlings varied from location to location. The calf/cow ratio varied from a high of 54 + 3.8 (SE)/100 cows in the Big River area on the south part of the island to a low of 24 + 1.9 (SE)/100 cows in the Parker River area. Overall, the calf/cow ratio was significantly higher in the pooled low density areas (48 +1.9 SE) than in the pooled high density areas (31 + 1.1 SE)(p<0.001). The yearling/100 cows ratios were also significantly higher in the low density areas (40 + 1.7 SE) than in the high density areas (29 + 1.3 SE)(p<.001). Lower calf and yearling numbers in the higher density areas may be a reflection of reduced productivity or reduced survivorship of young. The use of a helicopter to conduct the survey was very efficient and can be done with a minimum of disturbance to the animals provided large groups are classified from the ground. The ratios and their corresponding variances were calculated using the unweighted mean, the ratio estimator (binomial), and the jackknife estimator. The ratio estimator or the jackknife are recommended and gave similar results, with the jackknife giving a larger variance. Unbiased sampling to determine the adult sex ratio is more difficult because of the segregation of males as solitary animals or into male only groups.