Being an environmentalist does not necessarily make one either a liberal or convervative. Wanting to save our scenic areas, endangered animals, and historical sites and being concered about the dangers of overpopulation are issues that also attract many conservatives.
Field's group is very, very radical leftist. They openly espouse John Robbins's anti-meat philosophy. They also employ a large legal team to go after ranchers and private property owners.
http://www.earthsave.org
Again, the success of conservative radio is helping to fund these activities. Sorry if people don't want to hear it.