Most wild animals do a good job of taking care of themselves. However, you could work/volunteer at a wildlife rehab, some sort of wildlife conservation (like the Yellowstone Gray Wolf Recovery Project), park services, or wildlife law enforcment.
http://www.tc.umn.edu/~devo0028/contact.htm
http://wildliferehabber.com/modules/xoopsmembers/
http://www.nwrawildlife.org/documents/Stateprovgroups.pdf
http://www.wildlifecenter.org/about/vol_opportunities.php
http://www.nps.gov/personnel/rangers.htm
http://www.fws.gov/le/AboutLE/about_le.htm
http://training.fws.gov/learn/courses.htm
http://www.fws.gov/volunteers/
http://www.fws.gov/northeast/lawenf.html
http://www.fws.gov/jobs/wwd_law.html
http://www.fws.gov/jobs/wwd_sciences.html
http://www.gohuntgeorgia.com/documentdetail.aspx?docid=125&pageid=2&category=enforcement
http://www.state.tn.us/twra/pdfs/career.pdf
http://www.state.tn.us/twra/employment.html#wo1