They reopened for pitches recently for a limited number of freelance stories, which will run in November and December. They have detailed guidelines, including, “We’re primarily looking for conservation stories set in the United States right now. More specifically, we want the conservation stories that other publishers just don’t know how to handle — the stories you believe in, that get under your skin, that make your reporter’s radar scream, but you haven’t found a place to tell them yet.” Also see the list of things that interest them, and also the kind of articles they do not want (including pitches about their parent organization, the Center for Biological Diversity, or issues in which they have an active involvement). They pay $300-500 for 1,000-1,500 words; they distribute them under a Creative Commons license. See the pitch call here and their pitch guide is here.