Tracking wildlife

I watching a wildlife programme on TV the other day which had a feature about urban foxes. The naturalists  had fitted radio collars to some of the foxes and were able to track them over a wide area.One fox went off on a trek that lasted a couple of weeks and covered a distance of several kilometres.

In another programme radios have been attached to larger birds such as geese and ospreys to track their migration paths.
I wonder what frequency is used? One of the maturalists in the urban fox project seemed to be trying to DF a fox using what looked auspiciouslylike a 3 element 2m Yagi. I've seen similar antennas used o locate larger animals in Africa.

I would love to know what technology they use. My Kenwood TH-D7E APRS radio - despite being too big to use as a tracker for anythimg much smaller than an elephant -  can run for only a few hours with the GPS enbled and the power set to a sufficient level to enable tracking over a reasonable distance.using a less than optimal transmitting ntenna.