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Caribou are a large animal species found in the North American and Eurasian Arctic. The Porcupine Caribou Herd ranges in northwestern North America. The size of the Porcupine Caribou Herd depends on how many calves are born and survive and how many adult animals die during the year. The herd reached a peak in 1989 at 178,000 and then declined until 2001 when numbers were estimated at 123,000 caribou. The last population estimate in July 2010 was 169,000 caribou.*

The Porcupine herd did not grow as quickly other North American herds during the last decades of the 20th century. The birth rate during that period was high and managers suspected that the Porcupine herd experienced greater natural adult mortality than other barren ground caribou herds. Biologists believed that the population decline in the 1990s was probably related to weather conditions (high snow accumulations on the wintering grounds and short summers in the early 90s). *

Porcupine Caribou herd size. The data points on the graph are based on total counts of the caribou on their calving grounds. The census is done by taking photos from an airplane and counting the caribou. Managers were unable to count the herd between 2001 and 2010 for several reasons. In some years the caribou did not group well enough for pictures to be effective and in other years bad weather or poor visibility due to smoke from forest fires prevented the caribou count. Data source: Porcupine Caribou Management Board. From http://www.taiga.net/coop/indics/pchpop.html

Porcupine Caribou parturition rate (percent of cows that had given birth or were judged to be pregnant). This information is gathered from radio-collared caribou cows. Data Source: Alaska Dept. of Fish and Game. From http://www.taiga.net/coop/indics/pchbirth.html. 2008		Peary caribou. Photograph from L. David Mech, http://www.arctic.noaa.gov/gallery_wolf.html

Find more information (references and websites):

• * From http://www.taiga.net/coop/indics/pchpop.html
• Caribou website from US Fish and Wildlife (Alaska)