Three caribou from a larger herd that we saw in Denali National Park, Alaska. Look carefully at the one on the left. It has a belt around its neck, with a box at the bottom. Most likely a tracking device. I didn't see it at the time, but only later, at home, while zooming in on the picture.
Curiosity took me to web-searching and on to this page - http://taiga.net/satellite/. It's got some interesting information about tracking - why they do it, how they do it, etc. The basic technology is GPS satellites. An interesting rule of thumb is that the device shouldn't weigh more than 4% of the animal's body weight.