By: Nicole Stevens, Chesapeake Conservation Corps Member
A long-drawn-out and tolling cry,
That drifts above the chorus
Of shriller voices from the marsh
That April nights send o’er us;
A tender monotone of song
With vernal longings blending,
That rises from the ponds and pools,
And seems at times unending
~ John Burroughs, “The Song of the Toad”
Spring has sprung! Over the past few weeks, the weather has warmed, birds have sung, flowers have bloomed, and more and more frogs have left hibernation to serenade listeners with jubilant nighttime song. At ACLT, wood frog and spotted salamander eggs have appeared in our vernal pools and recent evenings and cloudy days have been filled with the croaks and peeps of thousands of singing frogs.
The prevalence of these wonderful animals is great news for the Parkers Creek watershed! Not only do they take care of bothersome insects, but frogs are also considered indicator species, so their presence “indicates” the health of an ecosystem. While they have lungs, frogs can also breathe through their skin (and therefore breathe while underwater), allowing them to have added protection from terrestrial predators and to hibernate undisturbed in aquatic environments. However, breathing through their skin also makes frogs especially susceptible to harmful pollutants since they may also absorb unwanted chemicals or diseases. The Parkers Creek watershed appears quite healthy since our frog populations are not suffering from contaminants and are instead thriving and growing!
More precise information about the type of species and number of individuals present at ACLT is being gathered through my capstone project. University of Maryland scientist Dr. Christopher Rowe, dedicated volunteer Kevin Donahue, and I set up several drift fences along an existing vernal pool on the PF2Bay trail and along one of the two new vernal pools installed last month. These fences, made from aluminum sheeting and tobacco stakes, are about 12 feet long and prevent amphibians from walking (or hopping) directly into the vernal pools. Instead the fences guide the amphibians into buried coffee cans where they are trapped for a short period of time until volunteers come to documents and release them. Volunteers will monitor these cans daily for two weeks each month from April to June and count and identify the species present. When there are multiple days in a row when monitoring cannot take place, the cans are covered and amphibians can freely move around the fences.
Frog call surveys are also being conducted periodically in the evenings. These require someone (myself or one of ACLT’s fantastic volunteers) to stand by the vernal pools at night and record which species of frogs they can hear and the intensity of their song. This data allows us to know what species are active at ACLT and get a rough idea of the number of individuals, even if we cannot see the animals. Data is also reported to FrogWatch USA, a program run by the Association of Zoos and Aquariums, where it joins a national database and can be used for larger science and conservation projects.
Through these monitoring efforts and from periodic visual observation (including the amazing Master Naturalist herp hunt on March 24th), we have seen a lot of species in ACLT’s vernal pools. Spring peepers, wood frogs, green frogs, and southern leopard frogs have been out and about, as have other amphibians like spotted salamanders and eastern newts! While the two manmade vernal pools I constructed last month (with LOTS of help from some amazing volunteers) have yet to have any breeding amphibians, recent rains filled the pools, and some insects and a spring peeper have moved in. Soon, these pools should be teeming with life, just like nearby natural areas!
Last month, I highlighted some of the frog species that may be active the earliest: spring peepers (Pseudacris crucifer), wood frogs (Lithobates sylvaticus), upland chorus frogs (Pseudacris feriarum), pickerel frogs (Lithobates palustris), and American toads (Anaxyrus americanus). These species will likely all still be calling throughout April, except for the wood frogs which complete their breeding season within just a few days. This month, many more species will emerge (or already have emerged) from their hiding places underground to join in the raucous evening symphony. Some of these species include the southern leopard frog (Lithobates sphenocephalus), the gray treefrog (Hyla versicolor), Cope’s gray treefrog (Hyla chrysoscelis), the Fowler’s toad (Anaxyrus fowleri), and the green frog (Lithobates clamitans). More information about these wonderful species and links to hear their calls can be found below!
Additional Southern Maryland Frog Species Active During April
Southern Leopard Frog (Lithobates sphenocephalus)
The southern leopard frog is the most common true frog species in the Coastal Plain, often found around backyard ponds and vernal pools (seasonal wetlands that only fill with water for part of the year). They have dark, roundish spots on their backs (hence the name leopard frogs), range in color from green to brown, generally grow to about 2-3.5 inches, and have two lighter-colored dorsolateral folds (raised lines) running down the edges of their backs. They greatly resemble the related pickerel frog, though their spots are less square and more uneven, and they lack the pickerel frog’s distinctive yellow patch on the inside of their thighs. Southern leopard frogs are great swimmers and may use their powerful back legs to jump into your local waterways! They are not very particular in the types of wetlands they occupy and may even be found in brackish (slightly salty) water. Listen for their chuckle-like call in the evenings or on cloudy days: Southern Leopard Frog Call
Gray Treefrog (Hyla versicolor) & Cope’s Gray Treefrog (Hyla chrysoscelis)
The gray treefrog and the Cope’s gray treefrog look identical to the naked eye and can only be differentiated through genetic analysis or by call by a trained listener. Both species are generally gray or green (and can change color in a few hours depending on their environment) with darker blotches on their backs. They are fairly small and generally only grow to 1-2 inches in length. Like all treefrogs, (Cope’s) gray treefrogs have slimy skin and large toe pads to facilitate climbing, though their skin is rougher than most other treefrog species. Since the two species resemble each other so closely, researchers are unsure how much the ranges of gray and Cope’s gray treefrogs overlap, but the two species together inhabit much of the central and Eastern US. Look for them in trees or even on manmade structures like your fences or deck. Both of their calls sound like fast, high-pitched trills, though the Cope’s gray treefrog’s call is a bit higher and faster. You may hear them singing in the evenings near vernal pools which are their favorite breeding areas: Gray Treefrog Call and Cope’s Gray Treefrog Call
Fowler’s Toad (Anaxyrus fowleri)
Fowler’s toad is one of the two true toad species found in Maryland, the other is the American toad. Like the American toad, Fowler’s toads are usually brown with short back legs for hopping and glands on the side of their heads that excrete toxins. These toxins aren’t particularly dangerous to humans, though you may not want to rub your eye after picking up a toad. The easiest way to differentiate Fowler’s toads from American toads is by the density of bumps (or “warts”) on their bodies. Fowler’s toads usually have 3-4 bumps per dark brown patch, while American toads generally only have 1-2. Fowler’s toads are usually 2-3 inches long and breed in a variety of wetlands, especially those that are shallow and have sandy bottoms. You may see them hopping through forests or meadows or hear their calls that sound a bit like a sheep saying “baaaa” or a series of short, repeated yells: Fowler’s Toad Call
Green Frog (Lithobates clamitans)
The green frog is usually brown in color (confusing, I know), though often has green markings above its snout that resemble a mustache. They are a fairly large species growing to 3.5 inches in length and are often confused with small bullfrogs. Like bullfrogs, green frogs have a circular tympanum, or external ear, which is larger than the eye in male frogs and the same size as or smaller than the eye in female frogs. To differentiate between a green frog and a small bullfrog, look at the arch that comes out from the eye. If it curves around the tympanum, you have a bullfrog and if the arch continues down the side of the animal’s back, you have a green frog! The green frog generally likes to breed in permanent ponds, though I have spotted some in vernal pools and in small roadside ditches as well. Green frogs usually remain within 1 meter of water as adults (except on rainy nights), so wetlands are a great place to look for or hear this species! If you hear a deep groaning call in early spring, chances are it’s a green frog: Green Frog Call