Relationship between calving time and physical condition in three wild reindeer Rangifer tarandus populations in southern Norway

Abstract

Time of calving in reindeer Rangifer tarandus varies between populations, but takes place around the start of the green season to ensure a stable food supply for doe and calf. Causes of variation in calving time was investigated by studying the three adjacent populations of North Ottadalen, South Ottadalen and Snøhetta, in Norway. The peak calving time was 12–14 May during 1996–1998 in North Ottadalen, 10 May in 1997 and 11 May in 1998 in South Ottadalen, and 22–26 May during 1996–1998 in Snøhetta. Comparing these results with recordings from 1969–1972, 1978 and 1985, peak calving time has been delayed by 6–8 days in North Ottadalen, and has advanced by 2–6 days in Snøhetta. In South Ottadalen, the peak calving time has remained almost constant. Analyses of covariance showed that calving time was negatively related to autumn dressed weight (P < 0.05), but not to mandible length (P = 0.15), and that calving happened later in Snøhetta than in North Ottadalen for the same level of autumn dressed weight (P < 0.05; 11.5 days) and mandible length (P < 0.05; 14 days). These results strengthen the hypothesis that delayed conception and calving is a consequence of relatively poor doe condition in autumn.