I guess there's always some wiggle room on most deployments. However, where I used to work, some of the guys at that department were conducting research on flying foxes as their migration patterns southern to northern parts of Queensland (Australia) were pretty much unknown (IIRC). The requirements there gets pretty tough. Also, the power consumption becomes a major factor as it will limit the amount of useful work the device can do, ie sensing, communication etc.

Anecdote: I learned about another project where they studied opossums. They put a collar with a small wireless device around their necks to track their movements and habits, but couldn't understand why a disproportionate amount of opossums died for some reason.... The reason was that the device had a small red LED that would blink to indicate that it was working, and the opossum, being a nocturnal animal became quite visible in the night, to the joy of all predators :) :S