Spring’s Croaking Chorus
Ten species of frogs and toads share our landscape, a rich assemblage of hopping amphibians for such a northerly clime.
Soon the hills will reverberate with the glorious voices of frogs. Voices that peep, quack, snore, tap, trill, and creak. Voices that sound like banjo strings being plucked, voices that chant bass notes on sultry evenings. These voices are the soundtrack of a healthy ecosystem. As they have for thousands of springs, they signal rebirth and an affirmation of life in all its mesmerizing diversity.
Frogs can do wondrous things. Some can essentially freeze solid, then, in an astonishing resurrection, thaw out, stretch their sinuous legs and hop away. Cryogenic scientists struggle to unravel their mysterious secrets.
Some can scale sheer glass surfaces like amphibian spider-men. One species can willfully change its colour to match its surroundings. Some frogs can poison their adversaries and some tadpoles can change their shape and colour to stymie predators.
Ten species of frogs and toads share our landscape, a rich assemblage of hopping amphibians for such a northerly clime. And the good news is, given the threats to many of their kind around the world, most of our frogs are doing very well.
Six varieties are common. Because our lightly populated landscape still contains ample fields, woodlands and wetlands, these species can be found throughout Headwaters. They are the spring peeper, grey tree frog, American toad, northern leopard frog, green frog and wood frog.
Four other species are more spottily distributed. The mink frog, a species more common in the Canadian Shield, reaches its southern limit in the hills, probably extending no further south than the village of Alton. The bullfrog, the bruiser of the frog clan in North America, is found only sporadically here. The chorus frog, a wee sprite that could perch comfortably on a bullfrog’s nose, is also more rare, as is the pickerel frog, a close cousin to the more numerous leopard frog.
Though all our frogs and toads depend on wetlands for breeding, each species has particular preferences. Some, like the American toad and the grey tree frog, are bold opportunists, breeding just about anywhere – ponds, lakes, swamps, roadside ditches, garden pools – even pool liners. Amphibian dousers, they seem to possess an almost magical ability to find these water sources. This allows them to shift their breeding sites from year to year, taking advantage of temporary pools that come and go on the landscape.
However, the breeding site selection of these amphibians is not entirely random. Toads, for example, discriminately test the waters, so to speak, for telltale evidence of the presence of wood frog tadpoles. Those omnivorous creatures consume whatever they can get their rasping mouthparts on, including toad tadpoles. Remarkably, if a mother toad detects the presence of wood frog tadpoles, she turns her warty back on the pond and hops away.
Unlike toads and tree frogs, wood frogs are very choosy about where they breed. They look for ponds that will dry up in the summer heat. Spring peepers and chorus frogs also prefer these temporary “vernal” pools.
This raises the question why so many amphibians – spotted and Jefferson salamanders also lay their eggs in vernal pools – entrust their precious larvae to ponds that could dry early and kill them. The short answer is fish, or rather the absence of fish, in the vernal pools. Avoiding amphibian-hungry fish trumps the spectre of early drying.
The Niagara Escarpment, beaded with innumerable such pools, is one reason we have so many frogs. Another is the presence of extensive woodlands. Some of our frogs are utterly tree-dependent. These include the aptly named wood frog and grey tree frog. Remove trees, and the shelter, food, humidity and shade these frogs need are gone.
Other predators that make a frog’s life perilous include giant water bugs, herons and raccoons. Of course, as masters of evolutionary adaptation, frogs are not entirely at the mercy of these predators. Some, like leopard and pickerel frogs, avoid pursuers with erratic, powerful jumps. Tiny, cryptically coloured frogs, such as spring peepers and chorus frogs, opt for concealment.
Several frogs, including pickerel frogs, emit toxic skin secretions that leave a bad taste in a predator’s mouth. Large glands behind the eyes of toads contain bufotoxin, a witch’s brew of chemicals that can cause seizures and convulsions in mammalian predators. Bullfrog tadpoles are believed to be toxic as well, a quality that allows them to swim unmolested with the fish.
Alas, no defence is absolute. Snakes feed on toxic toads and pickerel frogs with impunity. I once watched a garter snake open its mouth impossibly wide to swallow a large toad. The big gulp took about 20 minutes.
Another remarkable defence that one of our frogs has evolved is the ability to change colour. The grey tree frog’s scientific moniker is Hyla versicolor. The species name is most apt, for this chameleon-like frog can colour shift through a range of greys, greens and browns to match its surroundings.
Grey tree frog tadpoles also have a colour change capability, stimulated by chemical traces of predacious dragonfly larvae in the water. If the larvae are present, the tadpole tails will turn bright red. The theory is that the intensity of this colour diverts attention from the heads of the tadpoles to their expendable tails.
Even more remarkable is how our tree frogs survive the winter. Grey tree frogs, along with spring peepers and wood frogs, hibernate on land – not under a foot or so of insulating soil like the American toad – but simply by tucking themselves under a blanket of leaves on the forest floor. When the mercury falls, they become frogsicles!
Well not exactly – though that might be your impression if you held one in your hand. These frogs have the ability to transfer much of the water in their cells into the spaces surrounding those cells. It is in these extra-cellular cavities that freezing occurs. At the same time, water remaining in the cells is flushed with syrupy glucose or glycerol, natural antifreezes that protect the vital cell structures. This amazing survival toolkit allows wood frogs to live further north than any other amphibian, even beyond the Arctic Circle.
Hibernating in the leaf litter, these frogs are energized sooner by the warmth of the springtime sun than their pond-hibernating kin. This means, for wood frogs and spring peepers at least, an early start to their breeding activity, sometimes before the end of March. In the vernal ponds, where many of these frogs breed, this early start is crucial as their tadpoles race to transform before the ponds evaporate.
Although frogs are eaten by many other animals, they are effective predators themselves. They usually ambush their prey, waiting sphinx-like until insects, spiders and other invertebrates wander within striking distance. Bullfrogs eagerly devour anything they can fit in their cavernous mouths including mice, small snakes and other frogs.
Movement triggers feeding. A juicy bug clinging to a cattail leaf in front of a frog’s snout will be ignored as long as it is sensible enough not to move. A flick of its wings, however, or a waggle of its antennae will immediately arouse the frog’s interest.
In a water-filled ditch along Highpoint Sideroad in Caledon one summer, I had a rare opportunity to watch frogs actively feeding. A bloated beaver carcass bobbed in the water with three green frogs aboard. The carcass had become an amphibian buffet, with plump bluebottles and carrion beetles on the menu.
Be kind and tender to the Frog, And do not call him names,
As ‘Slimy skin,’ or ‘Polly-wog,’ Or likewise ‘Ugly James,’
Or ‘Gape-a-grin,’ or ‘Toad-gone-wrong, ’Or ‘Billy Bandy-knees’:
The Frog is justly sensitive
To epithets like these.
No animal will more repay
A treatment kind and fair; At least so lonely people say
Who keep a frog (and, by the way, They are extremely rare).
The Frog, by Hilaire Belloc
Despite the mind-boggling repertoire of survival adaptations that frogs possess, many species are ill-equipped to deal with the environmental changes we have wrought.
Of the more than 5,500 frog species in existence, hundreds are now on the casualty list of endangered and threatened wildlife. A great extinction event is unfolding because of our management of the planet. When the dust settles after this apocalypse, it is likely many species of frogs will be gone forever.
Although our local frogs appear to be doing well, they are not immune to the varied threats causing frog populations to decline elsewhere.
Bob Johnson, curator of amphibians and reptiles at the Toronto Zoo, says, “Loss of habitat in Ontario and globally explains about 75 per cent of amphibian declines.” This is no great surprise. Eliminating the mosaic of wetlands, fields and forests that frogs depend on pulls the ecosystem rug out from under their webbed feet.
Habitat loss is not the only threat facing frogs. Johnson sites pollution and the recent emergence of diseases. One is chytrid fungus, a pathogen that has ravaged frog populations in widely disparate parts of the world. It is spreading tsunami-like down the spine of Central America, sweeping away frog species such as the exquisite golden toads of Costa Rica. Poignantly, Johnson was probably one of the last people to see a breeding pair of these frogs. “For me,” he says “extinction is personal and extends to the extinction of experience itself – the opportunity for me to share an experience with you, my daughter or your readers.”
The wholesale disappearance of a species is not necessary for Johnson’s “extinction of experience” to occur. It can happen as well when a frog becomes locally extinct and we lose the opportunity to experience the joy and fascination of hearing and observing it in our own communities.
The water-permeable skin of frogs makes them especially susceptible to water-borne pollutants. Frogs lacking limbs or with extra limbs have been found in disturbing numbers at some sites in Canada and the United States. The causes of such deformities are not fully understood, but it is widely accepted that run-off from pesticides and fertilizers is among the factors.
Unlike pesticides, fertilizers do not affect frogs directly. Instead, they are thought to be the “push” that gets the deformity ball rolling. Fertilizers encourage the growth of algae in ponds, spurring a population explosion of algae-grazing snails. It’s not the snails that harm the frogs, but a parasite they harbour. The parasites leave the snails to complete their development in the bodies of tadpoles, where they can impair limb development.
Concern about frog populations inspired the creation of FrogWatch-Canada, a national frog monitoring program co-ordinated in Ontario by the Toronto Zoo. Headed by Bob Johnson, FrogWatch Ontario invites the public to submit information on where and when they have heard frogs calling.
Thousands of records have been contributed to FrogWatch Ontario since its inauguration in 1998. “These data can be used to look at long-term trends in populations, or shifts in calling and activity dates based on weather changes,” says Johnson. But as important is the role FrogWatch plays in engaging people with nature: “People can speak up for the creatures that cannot speak for themselves.”
Here in the hills we have a wonderful opportunity to speak up for frogs and act on their behalf. We can ensure that our hills, unlike so many places in the world, remain frog friendly. Obviously we need to preserve the wetlands and woodlands they depend upon. But we can also go a step further and attempt to grow frog populations by enhancing and creating frog habitat.
Landowners are crucial to such an initiative. “Reducing chemical use on lawns or near water bodies is an easy first step,” says Johnson. “Leaving grassy areas unmowed is also easy. This provides not only shelter from the sun, but areas where frogs can forage for the invertebrates that will also thrive there.”
Allowing natural corridors to develop between ponds and woodlots to permit safe movement between them is another good idea. Such linkages can also be brought about simply by not cutting the grass.
Where there are no ponds, they can be built, though resist the urge to stock them with fish if frog habitat is the goal. Digging temporary pools is an option as well. Locating such pools near woodlands offers additional breeding opportunities for frog and salamander species dependent on vernal pools.
Why should we bother to ensure that frogs continue to thrive in Headwaters? Well, to begin with, consider the role they play in the food web. Most frogs end up in the bellies of other animals. That is why frogs lay hundreds or even thousands of eggs. They convert the abundant energy found in wetlands into, in Bob Johnson’s words, “a form that is readily digestible (i.e., juicy frogs and tadpoles).” A spring bereft of frog voices would indicate not only an absence of frogs, but a dearth of other creatures that depend on them.
The crucial role frogs play in maintaining healthy biodiversity should be enough reason to protect them. But there are other compelling reasons as well. Frogs are a splendidly slimy, animated introduction to the natural world for children. The thrill of the chase, the splashing, the opportunity to get muddy, and finally a wriggling, writhing frog in hand is, in the vernacular of the young, “Really cool!”
My grade six class has the opportunity every spring to catch frogs at Finlayson Field Centre at Caledon Lake. Most of these urban kids have never seen a live frog before and they jump at the chance to find one. The guidance of caring adults is necessary, of course. Children need to understand that after suffering the indignity of capture, the frogs should be handled gently and quickly returned to their watery realm.
If frogs can open the eyes of children to the wonders of nature, they can also touch our souls. Bob Johnson again: “Frogs and other wildlife enrich the lives of many of us, just as art and music do. Just as art can provide meaning and inspiration and insight into the power of creation, so too can frogs.”
Frogs and toads also have a special role to play in keeping the environment healthy. Perhaps because they live “on the edge” between water and land, and have semi-permeable skin, frogs and toads are very sensitive to pollution and other environmental changes.
Worldwide, many species are declining in numbers or have recently become extinct. Monitoring frog and toad populations is one way to check the health of wetland areas. Frogs and toads can be used as indicator species, because they are vulnerable to changes in the atmosphere, the land, or the water.
To learn more about frogs, listen to their voices, or sign up to participate in the frog monitoring program at FrogWatch Ontario check out the following links:
Frogwatch Ontario can be accessed through this link:
Listen to Frogs
Listen to the voices of our frogs at:
(Click on the frog pictures and scroll down to the call file.)
Science teacher and naturalist Don Scallen will make a presentation on the Frogs of Headwaters on Saturday, July 21, as part of the Beauty in the Beast exhibition at Dufferin County Museum & Archives. He will give a second presentation on Caterpillars, Moths and Butterflies, including live specimens, on Saturday, August 18. Both presentations are at 2 p.m.
You can read Don’s regular blog: Notes from the Wild
I do not agree, look at that: http://www.mprnews.org/story/2014/07/02/frog-research
miner50 on Sep 30, 2016 at 7:31 am |