Earth & Sky

The following individuals were interviewed for today’s show. Our thanks to:

Fran Mauer
Wildlife Biologist
USFWS
Fairbanks, AK

Bruce Woods
External Affairs Officer
USFWS
Anchorage, AK

Cathy Curby
Wildlife Biologist
USFWS
Fairbanks, AK

More Resources:

Conversations about Caribou (ANWR Site)

Wildlife (ANWR Site)

Porcupine Caribou Herd (Taiga Net)

Caribou movements in a Late Spring Year US Fish and Wildlife Service 1987)

Author’s Notes:

The Porcupine caribou are named after the Porcupine river, which they cross on their yearly migrations between their summer calving grounds on the coastal plain of the Arctic National Wildlife Refuge (ANWR) and their winter homes in the southern part of the refuge and Canada. Caribou are large, hoved animals well adapted to the Arctic world of far North America, Siberia and Scandinavia. They’re in the same animal family as deer. They’re also sometimes called reindeer.

Late Migration
According to the ANWR website: “In most years a majority of the [caribou] herd’s calves are born on the foothills and coastal plain of the Arctic Refuge (see PCH Calving Distribution 1983-1999). In 1987, most calves were born in Canada and along the migration route. After the calves were strong enough to travel, the herd moved to the Arctic Refuge to get nutritious forage. In July the animals moved to coastal areas to find relief from mosquitos. In the last 18 years, this movement pattern has been observed only in the late springs of 1987, 1986, and 2000.”

But not everyone agrees that climate change is to blame for declining caribou. According to Jim Sedinger, a professor at the Institute of Arctic Biology in Fairbanks, Alaska, “Climate warming and earlier spring greenup has been an important hypothesis explaining the generally circumarctic increase in caribou, including those in the Prudhoe Bay oilfields. Thus, climate change may not be a good explanation for recent declines. Density dependence may be a better explanation. That said, there is no doubt that Alaska has expereinced delayed spring thaw that last two years. This may be related to shifts in the Aleutian low, which appears to have about a 20 year cycle, and could provide an explanation for poor production during the past two years.”

Benefits of the Coastal Plain of ANWR for Calving
According to the ANWR website: “The Refuge coastal plain is very important to calving success and calf survival in the Porcupine caribou herd. There are two main reasons for this. First, fewer brown bears, wolves, and golden eagles live on the coastal plain than in the adjacent foothills and mountains. As a result, the newborn calves have a better chance to survive their first week, until they become strong enough to outrun their pursuers. The Refuge coastal plain also provides an abundance of plant species preferred by caribou. Nutrition is very important to the pregnant cows, particularly after the long winter. The timing of snow melt and plant “green up” on the coastal plain coincides with their calving period. This gives the new mothers access to the most nutritious food when it is most important for their health and the proper development of nursing calves.”

Results of the 2001 Caribou Census
According to Fran Mauer, a wildlife biologist with the U.S. Fish and Wildlife Service, the 2001 caribou census, which uses hundreds of aerial photos to count each caribou, found about 123,000 caribou are present in the herd, compared to 129,000 in the 1998 census. It’s just the latest in a string of declines. The first caribou decline was seen in 1992, then again in each succeeding census year – 1994, 1998 and 2001. This winter (of 2001/2002), it appears that about half the caribou are wintering in Canada and the other half in Alaska. According to Stephen M. Arthur, of the Alaska Department of Fish and Game, “The [porcupine caribou] herd has declined by 31% since its peak population of 178,000 was recorded in 1989, but still is considerably more numerous than during the 1970s, when it was estimated at 100,000 to 110,000 caribou.”

Arthur continues, “The current decline apparently began during a series of hard winters from 1990-1993, which reduced calf production and survival. However, the herd continued to decline during the mid and late 1990s, when late-winter weather was less severe and calf production and survival were greater. More recently, persistent snow cover during May and June of 2000 and 2001 delayed the herd in reaching its preferred calving grounds on the coastal plain of the Arctic National Wildlife Refuge. This reduced survival of calves so that only 44-51% of cows were accompanied by calves at the end of June, the lowest rates recorded during more than 20 years of research on this herd. Thus, the herd was expected to continue declining. However, the 1.5% annual rate of decline since 1998 is less than the 3% average from 1989 through 1998, which suggests that survival of adults may have increased during recent years. The next census of the Porcupine Herd is planned for summer 2003.”