Stress
Just cross your fingers that none of the dolphins gives birth any time soon.
Sure, it's a happy event and all. Who doesn't want to see as many cute baby dolphins as possible in the world? That said...every time a baby dolphin is born, guess who needs to play nurse? That's right, it's the dolphin trainers, who need to monitor mother and baby twenty-four hours a day, for up to six months (source). What does that mean? A well-rested, healthy mother and baby dolphin...and a number of very, very tired and sleep-deprived dolphin trainers.
Aside from your at-times hectic schedule, you work reasonable hours that leave enough time for a family and social life, and you get your recommended physical activity each day and a few dolphin hugs to boot.