Green Serenade

It’s been rainy and cloudy for much of the last two weeks here along the Front Range and, while I could use some sunshine, there are some who are loving this weather. Who are they? Amphibians, of course! Amphibians are animals that spend part of their life as an aquatic animal and part of their life as a land animal. This includes frogs, toads, and salamanders.

Being a semi-arid state, Colorado has a relatively small number of native amphibians, but this is the time of year that they really shine. One in particular is very vocal right now. If you’re passing a marshy area, you might hear its creaky call; it sounds sort of like someone flicking the tines on a plastic comb. This is the western chorus frog (Pseudacris triseriata), a little frog (growing only up to about 1.6 inches or 40 mm long) with a big voice.

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Western chorus frog with human finger for size comparison. Photo by Benny Mazur. http://www.enature.com/fieldguides/enlarged.asp?imageID=19190
Western chorus frog with human finger for size comparison. Photo by Benny Mazur. http://www.enature.com/fieldguides/enlarged.asp?imageID=19190

The western chorus frog can be found throughout most of Colorado up to about 12,000 feet in elevation, but due to its small size and habit of going quiet when potential predators approach, it’s really difficult to see. They also blend in very well with their surroundings. Chorus frogs can be greenish-grey, reddish, olive, or even brown. Three dark lines down its back and one through the eye extending from the snout all the way down to the legs are diagnostic, though the lines can sometimes be absent. The frog also has a white line along the snout.

March through May is prime breeding season for chorus frogs in Colorado. I heard my first frogs calling this season at the end of March at Sawhill Ponds in Boulder. They were still calling in Fort Collins last week. Males are the most vocal and they call to secure a mate. Mating in frogs and other amphibians is called amplexus (“embrace” in Latin). The male grabs hold of the female from behind and fertilizes her eggs as she lays them. For western chorus frogs, they may lay up to 1,500 eggs, which are generally laid in what are termed vernal pools. A vernal pool is a temporary pond and they are extremely important habitat for amphibians of all kinds. The attraction of a vernal pool is that they are too temporary and too shallow to support fish, which are a major predator of tadpoles.

Egg mass of Western Chorus Frog; RG Johnsson; 1966. http://www.nps.gov/features/yell/slidefile/fishherps/frogstoads/Page.htm
Egg mass of Western Chorus Frog;
RG Johnsson;
1966. http://www.nps.gov/features/yell/slidefile/fishherps/frogstoads/Page.htm

Have you ever seen a frog egg? Unlike bird or reptile eggs, frog eggs aren’t surrounded by a shell. Because of that, they’re vulnerable to drying out, so they’re laid in water, often attached to grass or a stick. What’s really fascinating is that you can tell the difference between a frog egg mass versus a salamander egg mass versus a toad egg mass. Unlike frog eggs, salamander eggs are contained in an outer gelatinous casing, whereas toad eggs aren’t laid in a mass at all, but rather in long strands. If you’re a herpetologist, you may be good enough to narrow down which species laid which eggs.

Since the rain may not let up for awhile, why don’t you put on your galoshes and poncho and venture out into it? Who knows what you’ll see or hear?

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2 thoughts on “Green Serenade”

  1. Found your blog through a Google search of vernal ponds in Northern Colorado. Still hoping to find out where some might be located in Greeley or Windsor, in the next few month. But this was a very interesting article. We will be listening for the little froggy since we are nearing it’s breeding time.

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