The changing natural world at our doorsteps | Illustration and text by Patterson Clark
March 26, 2013
Spring peeper: Call of the cross bearer
By a shallow vernal pool, a loud, brittle PEEP pierces the early evening — and then another, and another. An amphibian love fest is underway.
Males make the noises; females make the choices, each picking her mate by the ring of his bell.
The male's big sound comes from a small sac that balloons out from his throat. Fully expanded, this membranous vocal sac is almost as wide as the inch-long body of the tiny frog.
The spring peeper's scientific name, Pseudacris crucifer, translates as "cross-bearing false locust." The peeper does sound insectlike — actually more like an Easter chick — and its leap resembles that of a locust, but the bold tattoo on its back looks less like a cross and more like someone doing a jumping jack.
But a cross seems appropriate when peak peeper season coincides with Easter. While working at Long Branch Nature Center in Arlington, Matt Neff says, he would "schedule 'peeper prowls' from the last two weeks in March until mid-April." One Maryland frog-call calendar indicates that peepers can be heard from early February through late May.
A freeze in the early weeks of spring can shut down a peeper party in the Washington area — and even immobilize the frogs. But high levels of glucose in the frogs' bodies will prevent ice crystals from rupturing their cells, allowing most of them to thaw out and get back to business.
"I recall hearing them on 50-plus-degree days in December," says Priya Nanjappa, the amphibian
and reptile coordinator for the Association of Fish and Wildlife Agencies. "Spring peepers tend to call opportunistically on warm days in the winter."
Perhaps "winter peeper" is a more apt name.
During summer, peepers lead a quiet, barely noticeable existence, hunting for small insects on or near the ground. A rain shower, however, can inspire a half-hearted song.
But this time of year, peepers are the most abundant frog heard by people volunteering for FrogWatch USA, a citizen science program developed by the Association of Zoos and Aquariums.
Neff, who now works for the National Zoo as an animal keeper at the Reptile Discovery Center, is developing a local FrogWatch chapter in hopes of monitoring at least 15 wetland sites by the end of the year. After his two-hour training session, participants take a written test and are challenged to identify the calls of 15 different local frogs and toads.
The spring peeper's call is an easy one to pick out, but all calls are distinctive once committed to memory: Cricket frogs sound like marbles clacking together; green frog calls resemble the clank of a tin can kicked down the road; green tree frogs honk like toy horns.
As the Christmas Bird Count and the Breeding Bird Survey do for avian species, FrogWatch data can help scientists gain a clearer picture of population dynamics in the increasingly threatened amphibian world.
About a third of the world's amphibian species face a litany of
threats: habitat loss, pesticides and other pollution, invasive species, overharvesting, climate change and disease. Many have already plunged to extinction.
Currently devastating amphibians around the world is the chytrid fungus, which in less than 15 years has spread to at least 287 species in 37 countries, wiping out more than 100 species. The most likely cause: transport of infected amphibians by the food and pet trades.
In the eastern United States, the fungus "is everywhere we've looked," says University of Maryland biologist Karen R. Lips. "All species can be infected, but die-offs have not been observed. There are some species with large-scale declines, but identifying the cause (or causes) is difficult because so many threats are present in the area."
SOURCES: Natural History Society of Maryland, Virginia Herpetological Society, EcoHealth, Amphibiaweb