On rainy spring evenings, have you ever encountered large numbers of salamanders and frogs crossing the road? Do you ever wonder where they came from and where they are going? New Jersey’s forests are home to a group of amphibians that breed in small, temporary wetlands called vernal pools. Within northern New Jersey, this group includes wood frogs, spotted salamanders, and Jefferson salamanders.
These salamanders are elusive, often concealed under foliage, moss, or in burrows created by small creatures. They belong to the Ambystomatidae family, earning the nickname “mole salamander” due to their subterranean tendencies. Feeding primarily at night on various invertebrates like earthworms and insects, they, along with wood frogs, play crucial roles in forest ecosystems as vital links in the food chain and are indicators of ecosystem health. Emerging from winter hibernation during rainy nights in late winter and early spring, they embark on journeys to vernal pools for mating and egg-laying, marking the onset of the amphibian migration.
If you follow us or any other wildlife organizations on social media, you may have noticed that our posts these last few days have been inundated with amphibians. It may seem like odd timing, given that our early breeders (wood frogs, spotted, and Jefferson salamanders) completed their crossroad migration last month. But the reason is simple – it’s Amphibian Week!
Close up of an American toad that hitched a ride during this year’s crossing. Photo Credit: Nikki Griffiths
Globally, amphibians are disappearing faster than any other vertebrate group. The International Union for the Conservation of Nature (IUCN) estimates that 41% of amphibian species categorized for their Red List are currently facing extinction. That estimate is likely conservative, given that these creatures are often small and difficult to survey, rendering many species data deficient. This is concerning from multiple perspectives. From an ethical standpoint, we don’t want any wildlife to go extinct except maybe, in my extremely biased opinion, certain types of ticks… (I began my career as a moose technician and saw firsthand the terrible consequences that winter ticks have on these behemoths). Beyond that though, amphibians are tasked with a lot of responsibilities and carry out their work efficiently and without complaint. The list is inexhaustive but here are a few things that amphibians are doing for us and our planet as we speak: filtering water, sequestering carbon, eating pests (like mosquitos!), serving as prey for countless predators, helping researchers study regeneration (with hopeful applications to the future of organ transplants), aerating the soil in your garden, indicating where water sources have been contaminated by pollutants, and giving everyone who meets them a reason to smile.
We’ve made it to the final “super species” in our “superhero” series though, like in the last post, we’re spotlighting an adaptation that aligns with one of the more notorious residents of Gotham City. Our local frog has all the chill, while this DC villain needs to chill… quite literally, as his sub-zero body temperature must be maintained to ensure his survival. Cryogenics expert, Dr. Victor Fries- better known as Mr. Freeze, had admirable intentions when he began his experimentation with ice. Unfortunately for him, accidental exposure to chemicals altered his physiology, necessitating the use of an air-conditioned suit and spurring a life of crime motivated by tragic desperation. The compound responsible for his transformation is thought by some to be glycerol, which also happens to be the key to the winter survival strategy of our favorite early breeding anuran- the wood frog (Lithobates sylvaticus).
Animals living in temperate climates must find ways to cope with the cold temperatures and reduction of food resources, characteristic of the winter season. Some species deal with winter by not dealing with winter… instead they migrate to milder conditions farther south. This is a path commonly taken by birds. Other animals have adapted to have a large body mass. This reduces their surface area and enables them to hold onto heat more efficiently. As a former moose biologist, I’m happy to give them a quick nod here. Many strategies exist across the natural world to increase the odds of persistence, but we’re here to talk about amphibians and, it’ll probably come as no surprise to you that they aren’t employing either of the aforementioned tactics.
Wood frogs are a vernal pool obligate species; they must have access to these temporary wetlands in order to breed and complete their lifecycle, but they don’t live in them all the time. Therefore, we do refer to them as migratory, but they only cover about ¼ to ½ mile during this annual pilgrimage, so temperature differences are negligible. Most frogs and salamanders in New Jersey endure the colder months by entering brumation- the “cold blooded” equivalent of hibernation. In this state, animals can drop their body temperature and metabolism to conserve energy. Some species burrow and use the ground as insulation. Others brumate in streams and ponds since water cools at a slower rate than air. Wood frogs cover themselves in leaf litter (for camouflage) and spend the winter comfortably as frog-cicles. That’s right- they essentially freeze solid and thaw once air temperatures become favorable again.
Under normal conditions, when a cell freezes, ice crystals form internally. These solids can then expand, which damages organelles and ultimately ruptures cell membranes. This leads to cell death. Compounded by damage incurred in blood vessels and dehydration, this would be a fatal situation for most animals. Wood frogs have found a hack to get around these devastating consequences.
A recently thawed wood frog huddled beneath a leaf. Photo credit: Nikki Griffiths.
As temperatures drop, wood frogs continue to produce urine but cease voiding it. Instead, the urine is concentrated into urea, which floods the frog’s bloodstream. The liver also goes into overdrive, manufacturing vast quantities of glucose, which causes their blood sugar to skyrocket as high as 100x normal levels (a better understanding of how this frog can avoid negative health effects under such conditions could certainly contribute to diabetes research in humans). The urea and glucose create a mixture that acts almost like antifreeze. Once ice crystals begin to form around the blood cells and internal organs, this homemade antifreeze infiltrates, allowing for the retention of water and protecting the frog’s cells from desiccation and explosion. They can maintain this state for up to 8 months.
This brumation strategy earns wood frogs the “northernmost amphibian in the western hemisphere” superlative as they can be found up past Gates of the Arctic National Park in Alaska.
The 2023 Amphibian season has begun! Drive carefully one upcoming rainy nights. Photo credit: Nikki Griffiths.
That’s a wrap on Mr. Freeze and our Super Species! The Amphibian Crossing is now in full swing. If you are going to be driving after sunset along roads that border ponds in the upcoming rains, watch out for migrating frogs and salamanders. Collisions with motor vehicles can decimate local populations rapidly so please slowdown!
I felt confident, after the mild conditions that we experienced in January and much of February, that March would skip the “lion” phase of the well-known adage and come in and out like a lamb. I was clearly incorrect…
In anticipation of the amphibian migration, I thought it would be fun to write about some of the most unique adaptations displayed by three early-breeding vernal pool obligates that we target during our Crossing program. These species require access to temporary wetlands in order to complete their life cycles and are thus at greater risk of motor vehicle collisions than other amphibians that don’t rely on these resources. As I started drafting this, I kept thinking about parallels between the behaviors that I chose for each species and superheroes/villains whose background and abilities relate. And so, I’m kicking off this series with our very own Wonder Woman, the Jefferson Salamander.
Citizen science projects are an amazing way for volunteers to contribute to ongoing research projects. By using volunteers scientists are able to extend the data collected for projects, and help more wildlife. The Amphibian Crossing Project is one of the ways CWF works with volunteers to protect imperiled wildlife.
