We spend a lot of time looking for junco nests in my field work, which means we spend a lot of time looking at the ground, which means we see a lot of these little guys:
Pacific tree frogs come in two main flavors: brown and green.
Some frogs stay the same color for their entire lives, but some can change from brown to green, or vice versa, depending on whether the background is dark (brown) or light (green). You can see how this might be handy if you want to blend in with the background.
It isn’t instant, perfect camouflage, though: it takes them days to weeks to change. So if you hop from the green grass to a brown stem, that slow kind of color change won’t help.
Instead, it’s thought that the slow color change helps the frogs match the general environment over the course of a season (Wente & Phillips 2003). An area might start out bright green in spring, then slowly dry out during summer, becoming more and more brown. A frog that gradually changed from green to brown would have a better chance of blending in with that changing background.
I’m not really sure where the frogs that aren’t green or brown fit into this, though. I haven’t seen mention of them in the papers I’ve looked at, but they’re definitely around. (Any herpetologists want to help out?) Possibly the “green” and “brown” categories include some shades that aren’t strictly those colors.
All of these shades can work well as camouflage.
But the frog does need to find the right background…
It’s fun to see how many color variations there are.
Wente WH, Phillips JB. 2003. Fixed green and brown color morphs and a novel color-changing morph of the Pacific tree frog Hyla regilla. The American Naturalist 162(4):461-473.