Influence of Population Growth on Caribou Herd Identity, Calving Ground Fidelity, and Behavior

Abstract

A large barren‐ground caribou (Rangifer tarandus granti) population (the Bering Seacoast Herd) historically ranged across southwest Alaska. The size of this herd peaked in the early 1860s but declined by the late 1880s. Caribou numbers remained low in southwest Alaska for the next 100 years. Biologists have argued that periodic dispersal has been an important factor in caribou population dynamics. However, others conclude there was no credible evidence that significant interchange between herds has ever occurred in Alaska. Since 1981, we monitored 318 radiocollared caribou and documented dramatic population growth, erratic movements, shifts from traditional ranges, and changes in migratory behavior. We also documented shifts in calving distribution that may contrast with conventional concepts of calving tradition and herd identity. Some biologists have concluded caribou herds can be considered closed populations for management purposes because the number of dispersing caribou is so small that it has no influence on population dynamics. We propose that the current definition of a herd may be appropriate for short‐term management; however, over long time frames and large spatial scales, metapopulations may better describe caribou ecology and be more useful in long‐term caribou conservation.

A conceptual model for migratory tundra caribou to explain and predict why shifts in spatial fidelity of breeding cows to their calving grounds are infrequent

“…In the Alaskan mountains, there are two examples of herds with increasing population sizes that shifted their calving grounds. The new calving ground overlapped the calving area of a smaller and neighbouring herd Valkenburg et al, 2003;Hinkes et al, 2005). Although information on caribou densities on the calving grounds is not available, it is reasonable to assume that they were high for the larger herd.…”

“…4000) traditional calving ground was 25 km away from the larger Mulchatna's (ca. 200 000) calving ground in 1994 (Hinkes et al, 2005). The smaller mountain herds (Yanert and Kilbuck) had different calving strategies (scattered rather than gregarious) than the larger herds.…”

“…As a result, changes in the geographic locations of area used for calving were documented, which led to questioning the concept of fidelity to these areas (e.g., Davis et al, 1986;Hinkes et al, 2005). The amount of overlap between annual calving grounds varies and the annual differences in overlap of consecutive calving distributions can show a consistent direction (Gunn et al, , 2008.…”

“…The two reported instances are from the Alaskan mountains, where the calving grounds of two large caribou herds shifted <25 km and engulfed the dispersed calving sites of two small herds Valkenburg et al, 2003;Hinkes et al, 2005).…”

Understanding the role of behavioral mechanisms and impacts of habitat fragmentation on structuring small declining populations

“…a road or region of human-altered habitat) between them. Although historical lack of demographic connectivity seems unlikely for mountain caribou given long-distance movement capabilities of some caribou populations (particularly barrenground caribou), the fact that the Mulchatna caribou herd expanded its geographical distribution during population eruption events, suggests that this population of mountain caribou may behave similarly and only expand via dispersers during such infrequent population eruptions (see Hinkes et al, 2005). If this is indeed how this population historically expanded and hence was demographically connected, then human-induced fragmentation may not be the direct cause of the population structuring, but more likely plays a secondary and exacerbating role (e.g.…”