If you are looking for an internship in ecology, check out the possibilities at TREES (toucan ridge ecology and educational society) on the Hummingbird Highway in Belize!
This research station is open for groups, but also for individuals. There is a research lab, library and the organization is hosted by a very professional staff.
The volunteering starts from 15usd a day. Internships from 25usd. But you will be sure to get to know lots about the neotropical flora and fauna.