Todd McLeish: Frozen frogs are thawing out for spring but face death on the roads
Wood frog
— Photo by Brian Gratwicke
From ecoRI News (ecori.org)
The onset of the coronavirus pandemic a yer ago coincided with the annual migration of frogs and salamanders to their breeding ponds, a trek that often results in mass mortalities as they cross roads trying to reach their preferred waterbody. The lockdown during the early stages of the pandemic last year gave a significant reprieve to amphibian populations, reducing roadway mortalities by as much as half, according to a New England researcher.
But this year, with traffic back to near normal levels, frogs and salamanders aren’t likely to fare as well. And wood frogs will likely be at the top of the list of roadkill victims.
In southern New England, wood frogs are one of the first signs of spring, according to herpetologist Mike Cavaliere, the Audubon Society of Rhode Island’s stewardship specialist. They are the first species to emerge from their winter hibernation, typically in mid to late March. And as soon as they awaken, he said, they hop to their breeding pools to seek a mate on the first night it rains.
“What’s particularly amazing about wood frogs is that they can produce a natural antifreeze that allows them to almost freeze completely solid in winter,” Cavaliere said. “This antifreeze is produced when the frogs start to feel ice crystals begin to form in late fall.”
Unique among frogs in the Northeast, the wood frog’s antifreeze is a chemical reaction between stored urine and glucose, which protects a frog’s cells and organs from freezing while allowing the rest of its body to freeze.
“Its brain shuts down, its heart stops, its lungs stop, everything stops for months. It’s like they’re in suspended animation,” Cavaliere said. “And once spring comes, they thaw out and the heart starts beating again. After about a day, they start hopping around, eating and mating right away. It’s an amazing feat of evolution that they’ve developed.”
Wood frogs are often joined by spring peepers and spotted salamanders in migrating to their breeding pools during rainy nights in March, but it’s the frogs that are killed in the greatest numbers.
“Road mortality is one of the great seemingly unassessed sources of pressure for amphibians,” said Greg LeClair, a graduate student at the University of Maine who coordinates The Big Night, an amphibian monitoring project to quantify the roadkill of frogs and salamanders during their spring migration. “We know that disease and climate are affecting amphibians, but road mortality has long been suspected to be a serious problem, though there is no data to quantify population declines.”
LeClair said that road mortality can be as high as 100 percent in some areas when traffic is high during the one night of the season that most migration takes place.
“The average is 20 percent of amphibians at any road crossing will get nailed by a car in a given year,” he said. “That’s devastating for some species.”
During The Big Night, volunteers at 300 sites around Maine typically find two living amphibians crossing the road for every one dead one. But last year, with far fewer vehicles on the road because of the pandemic, twice as many frogs and salamanders survived the journey. In fact, a study by the Road Ecology Center found that pandemic lockdowns last year spared millions of animals from roadway deaths.
“We had record survival, but we’ll never be able to replicate that data again,” said LeClair, noting the impossibility of experimentally reducing region-wide traffic levels like happened with the pandemic.
While last year’s reduction in road mortality probably resulted in a short-term increase in amphibian populations, LeClair said that doesn’t mean there will be more breeding activity this year, since it takes several years for amphibians to grow to adulthood and begin breeding.
“It will take a couple years to determine if amphibian populations benefitted from the pandemic. My suspicion is leaning toward no benefit,” he said. “Most amphibian populations are driven by juvenile survival more than adult survival, so impacts to juveniles have stronger impacts than impacts to adults. Dispersing juveniles last summer likely encountered normal-level traffic as they left the pool to find a territory.”
Whether wood frogs and other amphibians benefitted from the pandemic shutdowns, their increased survival rate last spring almost certainly benefitted other wildlife.
“Their eggs and tadpoles are a major food source for other animals in spring,” Cavaliere said. “It’s one of the first sources of protein available, so spotted turtles and other reptiles and amphibians will eat them, as will any other scavenger who’s hungry in spring and looking for protein.”
Those interested in helping scientists gather data about frog populations in Rhode Island should sign up to participate in FrogWatch through the Roger Williams Park Zoo. Online training for the program is available through March 31.
Rhode Island resident and author Todd McLeish, an ecoRI News contributor, runs a wildlife blog.
Todd McLeish: Pandemics threaten amphibians, too
Green frogs
— Photo by Todd McLeish
From ecoRI News (ecori.org)
As frogs and salamanders emerge from winter hibernation and migrate to their breeding ponds, herpetologists throughout the region are paying close attention to the growing number of diseases threatening amphibians in the Northeast.
The most worrisome is an infectious fungal disease called chytridiomycosis, or chytrid, which has caused major die-offs of frog populations in the tropics and elsewhere and is blamed for numerous frog extinctions in Latin America.
According to University of Rhode Island herpetologist Nancy Karraker, chytrid grows on the skin of frogs, and when it’s found on their drink patch — a site on their belly where they absorb water into their bodies — the fungus makes it impossible for the frogs to regulate how much water they absorb, causing them to become desiccated and die.
“Chytrid has been found in multiple species of frogs in the Northeast, but we haven’t seen massive die-offs here,” said Karraker, a University of Rhode Island associate professor of natural resources science who has studied frogs around the world. “But that doesn’t mean that die-offs haven’t occurred, just that they haven’t been at the scale we’ve seen in South America. So we can’t say it’s not a problem here, and it certainly could become a serious problem.”
Some scientists believe that the disease originated in African clawed frogs, which were shipped around the world for use in human-pregnancy tests from the 1940s to the ’60s. Many of the frogs escaped from captivity and could easily have spread the disease to native frogs in many places. Other scientists believe the fungus was ubiquitous around the globe and that, initially, the only frogs that died were those with compromised immune systems.
“I don’t know where the greatest weight of support is for those ideas today,” Karraker said. “But maybe our frogs aren’t as susceptible because they’re not facing the kinds of stressors that may have impacted frogs in other places. Or it could be something to do with their natural history. We just don’t know, and that’s partly why I’m worried.”
In 2010, Antioch University New England graduate student Mandy Gaudreau, working in collaboration with Lou Perrotti, conservation director at Roger Williams Park Zoo, in Providence, swabbed 47 frogs and toads at 11 sites in Rhode Island and detected chytrid in 21 percent of the samples.
“What struck me about her results is that most of the ponds where she found chytrid were manmade ponds — farm ponds, retention ponds,” Perrotti said. “Why was it in those and not in the natural wetlands?”
He also wonders whether climate has an effect.=
“Frogs in Panama got wiped out. Costa Rica got wiped out. It seems like it’s worst at that certain temperature range,” Perrotti said. “Maybe our winters knock it back and keep it from becoming prevalent. Tropical frogs don’t have the seasonality that we have here.”
Chytrid, however, isn’t the only disease threatening amphibians and reptiles in the Northeast.
Scott Buchanan, a herpetologist at the Rhode Island Department of Environmental Management’s Division of Fish and Wildlife, is particularly concerned about ranavirus, an infectious disease that has caused die-offs of reptiles, amphibians, and fish in 20 states, including box turtles in the Northeast.
In frogs and toads, it especially affects the tadpole stage, causing skin hemorrhages, erratic swimming, buoyancy problems, and the inability to right themselves in the water.
“We know it’s here, it’s in our environment, but if and when it becomes active is hard to predict,” he said.
Buchanan is also tracking a fungal disease in snakes, a herpes virus in turtles, and chytrid in salamanders.
“Salamander chytrid has had devastating effects on salamanders in Europe over the last five to ten years, and it’s considered an eventuality that it will be brought into the U.S. one way or another and run through our salamanders,” he said. “The eastern U.S. is a global hot spot of salamander diversity, and a lot of research is going on now to determine how virulent it is, are particular species susceptible, and what are their natural defenses.”
“What’s notable for us,” Karraker said, “is that it’s usually really hard to change the rules for importing animals for the pet trade, but in 2016, legislation was passed that prevented the import of 201 species of salamanders to prevent the introduction of the disease into the U.S. That’s a landmark bit of legislation to protect our native species.”
Buchanan said it’s up to biologists and others working in area wetlands to follow strict protocols to prevent the spread of the diseases, such as regularly disinfecting their boots, equipment, and tools as they move from site to site around the region.
“We have to be vigilant about potentially transferring diseases from one wetland to another,” he said. “Because we move from one wetland to the next throughout the day and throughout the season, there’s real potential that we could move it around with us, and we often go to the most important sites and monitor the most sensitive species.
“It’s something we take really seriously. We know how quickly things can change here, we know disease pandemics can happen quickly, move around quickly, and cause devastating impacts on populations. And if it doesn’t wipe them out completely, it can take decades for them to recover.”
Todd McLeish, an ecoRI News writer, also runs a wildlife blog.
Tadpoles