Stress
Here's a pro-tip: If your job has the word "rescue" in the title, there's probably going to be some stress.
Here's another: The word "wildlife" involves wild animals.
Janice the barista wakes up every morning and makes cups of coffee. On a very stressful day, she'll deal with awful customers, the coffee machine will break down, and weird smells will leak from the bathroom.
A wildlife rescuer, however, wakes up every morning and rescues wild animals. On a very bad day, they'll get into a fight with a bear and have to be taken in for a blood transfusion and emergency rabies shots.
You'll go into extremely dangerous situations in all weather conditions, sometimes even venturing into areas affected by natural disasters and oil spills. Plus, oddly enough, wild animals don't really like it when two-legged creatures jab them with hypodermic needles. You will get scratched, bitten, and urinated on, plus you're at increased risk for zoonotic diseases (source).
And then there's the emotional stress.
You became an animal rescuer because you want to save lives—but you can't save every life. That's a lot to take home with you. Janice the barista goes home, turns on her Spotify, and forgets all about mean Mr. Thompson and his demanding mocha order. You won't have such an easy time. On days like these, it'll help to remember the success stories, and hopefully you can take comfort in knowing you stopped a creature's suffering.