Hooray for America's nature. One big reason it's there to treasure: the National Wildlife Refuge System, the world's premier network of public lands devoted to wildlife conservation. The Refuge System turns 113 on March 14.

Wait! Think before you aim that camera at a national wildlife refuge. It may be habit-forming. That’s been true for four standout nature photographers – each hooked on prowling a favorite refuge in hopes of locking eyes with a bird or fox, capturing light and color, and probing the mystery of our animal natures.