Porcupine Caribou Herd Indicators:

Herd population
 
Birth rate
 
Early plant growth in calving areas
 
Snow depths at Old Crow

See also:

Porcupine Caribou Herd Information

Arctic Borderlands Ecological Knowledge Co-op

    Larger version map showing 1983-2006

What is happening?

• On these maps the green represents calving areas for each year, with the darker green representing the areas of highest use. The maps are based on the annual calving sites of radio-collared cows (average of 40 per year)
• The general calving distribution of the herd follows the coastal plain from the Hulahula River, Alaska in the west to the Babbage River, Yukon in the east. The area of concentrated use occurs primarily on the Arctic Coastal Plain in Alaska. When environmental conditions make it difficult to reach the Alaskan Coastal Plain as happened in 1986-89 and 2000 a greater proportion of the calves are born in Canada.
• In 2006 most calves were born on the Yukon coastal plain. Why didn't cows reach their traditional calving area in Alaska? It does not appear to be due to snow conditions because most areas of the Alaskan and Yukon coastal plain were free of snow by late May. Based on information from caribou with satellite collars it appears the spring migration started about two weeks later than normal.

Why is it happening?

• The area used for calving contains abundant forage soon after calving and has fewer predators than other regions. No comparable alternative habitats are available.

Why is it important?

• Abundant forage and low predator numbers are critical to the survival and development of calves as 50% of first year mortality occurs in the first month after birth. The highly nutritious forage found in the calving area is very important for adult cows because the energy demands of milk production are very high.

Technical Notes

• A computer program was used to calculate each year's calving range and concentrated calving areas based on the calving locations of radio-collared cows. The data and analysis are the work of ADFG, USGS, Biological Resources Division, and US Fish and Wildlife Service.
• Analysis method: Contours were generated by analyzing each annual set of calving sites using a method called "Fixed-kernel with Least Squares Cross Validation" (Seaman, D.E. and R.A. Powell. 1996. An evaluation of the accuracy of kernel density estimators for home range analysis. Ecology 77(7):2075-2085; Seaman, D.E., B. Griffith, and R.A. Powell. 1998. KERNELHR: a program for estimating animal home ranges. Wildl. Soc. Bull. 26:95-100).
• More information on the colour coding:
  • Dark green - concentrated calving area
  • Medium green - the annual calving ground; the area in which you would expect to find 99% of all calving sites for that year.
  • Grey boundary - the extent of calving 1983-2006; this is the outer perimeter of all annual calving grounds, 1983-2006

    Map of concentrated calving areas, combined for 1983-2006