In the Woods: A Chorus of Frogs

Walking around town the other evening, I couldn’t help but notice the sound of frogs. Our earliest vocal amphibians are boreal chorus frogs (Pseudacris maculate), with a sound much like running one’s fingers across a plastic comb; you can hear them at fieldguide.mt.gov/detail_AAABC05130.aspx. These one-inch frogs are generally light brown with dark brown spots. Skin color can vary and may be green, gray or red instead. The most noticeable mark is probably a long spot, almost a dark line, which extends from their nose, through the eye, to the groin. Another line runs most of the way down the back.

Froggy Went a Courtin’

Most small frogs breed in the spring with their young in a survival race against hot and dry weather. To avoid predators, namely fish, many frog species have evolved to lay their eggs in early spring water bodies, such as irrigation ditches, snow melt puddles, small ponds and other wet areas. While this reduces the risk of being eaten, it also means the future frogs have to complete their egg and tadpole stages – entirely in water – before their home dries up. And of course, there is still the chance that a passing critter will lap them up. Some adult frogs undoubtedly mistake road ruts as suitable breeding sites as well, with predictably unfortunate results.

The journey from egg to tadpole to froglet takes a couple months for most species. Eggs are laid in clumps or strings, often in the hundreds, attached to submerged vegetation. Tadpoles eat aquatic plants; adults mostly eat insects. They are eaten, in turn, by a great number of predators, including birds, fish, other frogs, some rodents and canines.

Dozens of Cousins

Within the next few weeks, at least two more local frog species will join the choir. In general, frog sounds are made to send specific messages, ranging from “Hey, Babe” to “Go Away”, or “Yipes!” Many can make calls underwater. Locally, you should soon be able to hear northern leopard frogs (Lithobates pipiens) with their throaty, almost rubbery rattle (check out http://www.californiaherps.com/frogs/pages/r.pipiens.sounds.html). These are the large, smooth, green frogs with distinctive spots and very long legs that they fold behind their butts. Because they are rather easy to see and fairly easy to catch, leopard frogs tend to be popular with young kids (but perhaps not parents?).

The much rarer boreal toad (Bufo boreas) is also found on the Forest, with a clucking sound similar to a high-pitched chicken (www.californiaherps.com/frogs/pages/b.b.boreas.sounds.html). Interestingly, the male boreal toad has no vocal sac so HOW it calls remains a bit of mystery. Boreal toads are round and fat with “warty” spots. They live in a variety of wet habitats at altitudes between 8,000 and 11,500 feet.

Unfortunately, boreal toads have suffered dramatic population declines in the last 20 years, mostly due to a fungus called chytrid (“ki-trid”). Chytrid is believed to slowly suffocate frogs and toads by attacking the skin through which they breathe and has been found throughout the world. Since chytrid doesn’t usually attack frogs, some scientists think the amphibians are being weakened by other environmental stresses, such as pollution. Chytrid has been described as the worst infectious disease ever recorded among wildlife in terms of the number of species impacted and the severity of the impact. To date, no cure has been found.

An Evening Walk

Cool evenings, right at sunset and especially after a rain, are the best times to hear frogs. As indicated above, the edges of wet areas provide the best chance of hearing at least one, and hopefully, several species. Given their rather low position on the food chain, they tend to be skittish and shy so it will probably be necessary to stand silently for a few minutes until they think the danger – your presence – has passed. You can also encourage small frogs, such as chorus frogs, on your own property by providing or protecting a bit of the habitat they desire.

Longing, a bit impatiently I will admit, for hotter weather, it’s “cool” to relish these early spring days that are just fine for frogs. Hope to see you in the woods, too.