No flashy prizes - your winning image just becomes one of the 12 in the Conservancy's annual calendar and is shown off on the web. You retain all rights but grant the Conservancy non-exclusive worldwide rights to publish your image.
They say:
"We are especially interested in images that showcase the wide range of habitats across our planet, including all types of forests, grasslands, lakes and rivers, deserts and arid lands, rainforests, marine habitats and coral reefs.
"Please do not include photographs of pets or domestic animals. Images of captive animals photographed in zoos and commercial game farms are also prohibited, however photos from state and national wildlife preserves are allowed."
They say:
"We are especially interested in images that showcase the wide range of habitats across our planet, including all types of forests, grasslands, lakes and rivers, deserts and arid lands, rainforests, marine habitats and coral reefs.
"Please do not include photographs of pets or domestic animals. Images of captive animals photographed in zoos and commercial game farms are also prohibited, however photos from state and national wildlife preserves are allowed."
You can submit images through a Flickr group or manually. The details are here.
Whether you're interested in submitting an entry or not, that site's a glorious browse of nature photography.