I work in water resources and we hire ecologists (classified as environmental scientists) to survey populations of aquatic organisms (everything from algae to river otters) as well cull overpopulated species like geese. We also have environmental scientists employed at our freshwater mussel hatchery and who operate a fish ladder (allows migratory fish to safely traverse dams). You can find similar positions in many local and state conservation districts, natural resource management and environmental agencies. A good number of positions can be found with non-profits and in academia as well. If you're interested in working with larger animals your best bet is probably a game commission, department or agriculture, park service, zoo, or wildlife refuge.
Keep in mind that even with a field position you will likely be expected to spend sometime in an office preforming tasks like filing reports, analyzing data, inventorying equipment, and applying for grants. Good luck with your studies!