Stress
While nobody would put "zoologist" on a Top Ten list of stressful jobs, there is definitely some stress to be found. Hanging out in the jungle and observing the social habits of gorillas might seem pretty chill, until the gorillas suddenly decide they're not cool with you anymore. Running from a 500-pound animal that can literally rip off arms—yeah, that's stressful.
Since hardly any zoologists actually work in the field, it's more likely that you’ll deal with much more mundane stressors. There'll be the stress of getting that article published, dealing with your jerk boss at the lab, or trying to keep freshmen interested in the migration patterns of butterflies. Hmm, we think we'd rather deal with that gorilla.