A Chorus Line?

These guys finally warmed up enough to make some noise last weekend:

Western Chorus Frog, (Pseudacris triseriata),
Van Patten Woods FP, Lake Co, IL 3/29/04

This is a Western Chorus Frog, (Pseudacris triseriata). It's a member of the family Hylidae, often called Tree Frogs for their habit of climbing trees.

Striped Chorus Frogs are our first frogs to call in the spring, and if you've ever been close to a pond full of them, you know where they got their name. A single frog sounds like someone running a fingernail along a comb, from the broad side to the narrow one. A whole pond of them sounds like a fairly high-pitched white noise generator, and they can be heard for a surprising distance. Seeing them, though, is really difficult -- I got this shot by spending 15 minutes knee deep in cold water, and if there was emergent vegetation to deal with I probably wouldn't have.

Any critter that's that hard to spot is probably dealing with a lot of predators, and these guys are no exception. Small frogs are eaten by everything from larger fish to really big diving beetles or dragonfly larvae to Red-shouldered Hawks. Their tadpoles are even more vulnerable.

Another way that these guys avoid predators is to breed in temporary ponds, where aquatic predators can't survive the summer. But that requires quick development -- if the pond dries up, the tadpoles die. On Isle Royale, Smith found that this dynamic limited the frogs to certain ponds, ones that stayed wet long enough for tadpoles to develop but not long enough for predators to colonize. (1) In SE Michigan, Skelly found that Chorus Frogs colonized temporary ponds while these guys used permanent ponds:

Spring Peeper (Pseudacris crucifer),
Ridges Sanctuary, Door Co, WI  8/12/2013 

This is a Spring Peeper, (P. crucifer). It's another early tree frog, as it's name suggests. Doing some manipulations enabled Skelly to determine what was driving the difference in pond usage, with Peepers developing more slowly and therefore being more susceptible to the ponds drying, while Chorus Frogs were able to develop quickly and avoid the ponds drying out, but were more susceptible to predators if they were present. He noticed that Chorus Frog tadpoles spent more time moving while feeding, which would help explain both their faster development and their greater risk of predation, and therefore the difference in how they use the environment. (2)

We often summarize natural selection as Survival of the Fittest, and ask which species is the best adapted to the environment. But as these frogs point out, there are many ways to use your environment, and the fittest frog is the one that fits its strategy to it's own little bit of the world around it.


(1) Smith, D. C. (1983). Factors controlling tadpole populations of the chorus frog (Pseudacris triseriata) on Isle Royale, Michigan. Ecology, 64(3), 501-510.

(2) Skelly, D. K. (1995). A behavioral trade-off and its consequences for the distribution of Pseudacris treefrog larvae. Ecology, 150-164.