See also:

Caribou population
 
Caribou birth rate
 
Caribou calving habitat use
 
Off-site: Porcupine Caribou Herd

Arctic Borderlands Ecological Knowledge Co-op

What is happening?

• This graph shows the variation in calf survival during June, a critical period shortly after birth. The number of calves surviving their first few weeks varies from year to year (no data was collected in 2004).
• In 2010 survival was high and researchers estimated 76% of calves survived, slightly above the long term average of 74%. They caution that due to bad weather in June they were only able to check on the status of 40 cow-calf pairs and this is a smaller sample than usual.
• In 2009 early calf survival was only 56% and matched the low point reached in 1993. Pregnancy rates were about average in 2009 so this indicator suggests the quality of calves was poor or conditions such as weather or the number of predators were worse than usual.

Why is it happening?

• In some years, when most calving occurred in Canada (e.g. 2000 and 2009), the birth rate has been low. This might be caused by loss of calves when the herd continues to move west into Alaska and crosses several major rivers. In 2007, calving occured in Canada but the survival rate was very high (83%). Calving occurred a few days earlier in 2007 so calves may have been better able to travel As well, pregnant cows may have been in better shape to begin with becasue the wintering range (in 2006-07) occurred further north than some years so the spring migration was short.

Why is it important?

• The early calf survival rate is an important indicator of how the population may grow in future. In years when the death rate of calves is high there will be limited opportunities for population growth.

Technical Notes

• In early June radio-collared caribou cows are checked for signs of a successful pregnancy (i.e. calf at heel). These females are then re-visited in late June to see how many still have calves alive.
• This measure does not reflect the death of calves that are lost at birth as only successful cows with calves are followed later in June.
• No information is available for 2004 because bad weather prevented flying.