Hi Christina,
There is not one simple answer to your question about why our Caribou herd is currently on the decline.
Briefly, some of the factors include; Caribou herds by nature go through increases & decreases of herd size from time-to-time, the Mulchatna herd got REALLY big and ate most of the good feed in thier traditional living area-which pushed them to different area's, hunting pressure-specifically on mature bulls-as been at an all time high for the past 5 years, Wolf populations are at an all time high-meaning predation is taking a big toll, the herd encoutered some type of "hoof rot" desease a few years ago, the bull-to-cow ratio & calf recruitment rate is down, ..........these are some of the major contibuting factors. As I mentioned before there is not one simple answer, but a complex series of events that has lead to thier current decline statis.
On another note, one time I was doing a Caribou survey and took a picture from 1,000 agl, during late Spring-over thier calving grounds, and it was estimated that there were in excess of 120,000 Caribou in that one photo!
Good Flying...>Byron