Winter range drift in the George River Caribou Herd: a response to summer forage limitation?

Isabelle Schmelzer,Robert Otto

doi:10.7557/2.23.5.1690

Abstract

Space use by the George River caribou herd (GRCH) changes in correspondence with migration patterns. The traditional range of this herd encompasses an area of approximately 900 000 km2. Range use is seasonal and includes travel to traditional calving grounds. Winter range use however, is more variable. The GRCH has grown rapidly from 5000 animals in 1954 to approximately 775 000 in 1993. Beginning in the mid 1980s, the calving and summer range habitats of the GRCH have deteriorated, resulting in a decline in physical condition and subsequent poor calf survival and low pregnancy rates. We assessed the importance of the winter range as a food source compensating for poor summer range quality through an evaluation of winter range drift and use intensity. We hypothesized that if winter ranges provide a compensatory source of forage, then George River caribou should avoid sites heavily used during the previous winter at a population level. Winter ranges for the GRCH were calculated using 4300 caribou locations obtained 1986-2000. We found that in spite of a doubling in net range area, the size of annual winter ranges did not increase, indicating the occurrence of range drift. Further, George River caribou exhibited avoidance of wintering areas at several spatial scales. Avoidance occurred across a use threshold, where the degree of use (or density) during the previous winter determined the level of avoidance during the subsequent winter. As the spatial scale decreased, the degree of avoidance increased. Caribou significantly avoided areas used the previous winter at spatial scales below and including 245 km2 (corresponding to a 75% use distribution). Results suggest winter foraging allows caribou suspend the effects of density-dependent summer forage limitation on herd productivity. As such, analysis of GRCH population trends should be considered in light of both summer and winter range resources.

Highlights

The migratory George River caribou (Rangifer tarandus) herd (GRCH) is a vital wildlife species of the taiga of Labrador and Northern Québec, and has been an integral component of the way of life for aboriginal peoples for many centuries
Study Area The George River caribou herd occupies much of the Ungava peninsula of Northern Québec and Labrador encompassed between the latitudes 54' and 61'N, an area extending from Hudson Bay to the Labrador Sea, approximately 900 000 km2 (Fig. 1)
Range Expansion and Drift The cumulative winter range of the George River caribou herd doubled in size during the period 1986-2000, from 392 796 km2 (1986-1989) to 811, 138 km2 (1998-2000) (Fig. 2)

Summary

Introduction

The migratory George River caribou (Rangifer tarandus) herd (GRCH) is a vital wildlife species of the taiga of Labrador and Northern Québec, and has been an integral component of the way of life for aboriginal peoples for many centuries. In 1985, Huot and Goudreault documented an unusual phenomenon for a northern ungulate: female caribou appeared to increase their fat reserves over the winter. They believed that the surprisingly poor fall condi¬ tion of females was related to a sampling bias. Couturier et al (1988) presented data confirm¬ ing that the fat reserves of female caribou were bet¬ ter in the spring than in the fall in during the 1980s Their explanation for this unique phenomenon among caribou was based on the deterioration of the calving grounds of the G R C H. Expanding on that theory, Couturier et al (1990) proposed that caribou might be using the winter range to compensate for the poor quality of the summer range

Objectives

Methods

Results

Conclusion