Small Frogs

Wood Frog

During the warmer months Ontario’s wetlands come alive with the music of nature. Birds are not the only creatures that sing or call in order to attract a mate; frogs do, too! In the spring and early summer large numbers of frogs migrate to bodies of water to find a mate. Some frogs, such as the Wood Frog and Spring Peeper, prefer temporary woodland pools, while others, such as the Green Frog, use any permanent water body from lakes to ponds to streams. Western Chorus Frogs breed in fishless pools of water that are at least 10 centimetres deep, such as rain-flooded meadows and ditches, while Bullfrogs prefer large, permanent bodies of water.

There are three general types of frogs and toads in Ontario: true toads, treefrogs and true frogs. Most people are familiar with true frogs such as Bullfrogs, Green Frogs and Leopard Frogs. These are the ones that can be seen sunning themselves on logs and lily pads or lurking among the emergent vegetation along the shore with just their eyes visible above the water’s surface. These frogs are large and conspicuous and impossible not to notice if you spend any time near the water during the summer.

Green Frog (2009)

Treefrogs, which usually have special toepads for climbing, are smaller and much more difficult to see outside of the breeding season when adults disperse to forests and upland habitats well away from the water. There are three treefrog species in Eastern Ontario: the Gray Treefrog, Spring Peeper, and Western Chorus Frog. Although I frequently hear all three during breeding season, the only species I’ve had any luck seeing is the Western Chorus Frog when I saw several at Nortel a few years back and one there this year. Prior to 2014 I’d never seen a Gray Treefrog before, and a Spring Peeper only once, in Cambridge.

This year I got lucky with my two nemesis frogs. While visiting the Old Quarry Trail back on May 11th I came across a family peering into the water along one of the boardwalks. Something was moving in the water, and they weren’t sure whether it was a tiny turtle or a frog. When at last it settled on the bottom I noticed the large “X” on the back and realized it was a Spring Peeper…and that it had eight legs! There were actually two small Spring Peepers, and they were mating.

Spring Peepers

Spring peepers are difficult to find as they are mostly active after sunset, and spend most of their time in the leaf litter of forested and shrubby upland habitats once breeding season ends. One of the earliest frogs to start calling in the spring, the Spring Peeper gives a single, loud, high-pitched “peep” repeated over and over. A pond or wetland full of Spring Peepers calling can be deafening up close, and the noise can be heard over a kilometre away. The only frog in Ontario which has a dark “X” on its back, it is unlike the other treefrog species in that it rarely climbs more than a metre above the ground.

Spring Peepers

Wood Frogs are true frogs, not treefrogs, although they, too, are quite small and are more likely to be found in the woods than in ponds once the breeding season ends. Although not a defining characteristic, true frogs have a ridge of skin extending from behind the eyes down the back known as a dorsolateral fold; they also usually have smooth, moist skin. I have more luck finding Wood Frogs than any of the other small frogs, and was surprised to come across one at the Rideau Trail one day in May. It was sitting on a log in the large puddle that usually forms underneath the first boardwalk each spring. I saw the dark shape on the light, reddish wood and stopped to take a look. This was significant to me, for although I’d heard Western Chorus Frogs along this trail every spring, I’d never heard or seen a Wood Frog.

Wood Frog on a Log

The Wood Frog is the only frog in Ontario which sports a black mask. It is also the most widely distributed amphibian in Canada, inhabiting every province and territory. In fact, the Wood Frog has the northernmost distribution of any frog species. It hibernates under logs or leaf litter on the forest floor, where it is able to survive temperatures as low as -12°C and the freezing of 60-70% of the water in its body. Glucose produced in the liver acts as antifreeze and prevents the cells from bursting. Although the Wood Frog’s heart stops beating and the interstitial fluid freezes (the fluid that surrounds the individual cells of the body), it thaws out in the early spring where it leaves the woods to find a pond in which to breed.

Wood Frog

I finally set eyes on my first Gray Treefrog later in the month. Our monthly Birds Committee meeting at the Fletcher Wildlife Garden ended just before dusk, so Anouk and I took a walk around the garden and down to the pond where we could hear a number of Gray Treefrogs calling from the vegetation surrounding the water. We spotted a Swainson’s Thrush and what looked like an Eastern Wood-pewee on our walk, and spent some time searching for the frogs we could hear calling from right in front of us. We had no luck, circled the garden, and then after full dark had descended found two that were sitting in the middle of the path when they hopped out of the way. Anouk shone a light on one of the frogs while I took its picture.

Gray Treefrog

It was bigger and plumper than I had expected. I thought we would be looking for a frog as small as the tiny Spring Peepers I had seen earlier; this was at least twice the size of a Wood Frog. Unlike the smooth-skinned true frogs, the Gray Treefrog has rough green, brown or grey skin with large darker blotches on the back. The skin of these frogs provides excellent camouflage against bark and lichens, particularly as they can change colour from gray to green or brown, depending on their environment or activity. Like the other treefrogs, it has large suction-cup-like toe pads used for climbing trees, or the sides of buildings where it sits beneath the lights at night catching insects attracted to the light.

It was fantastic to finally see my first Gray Treefrog and to observe a mating pair of Spring Peepers. It will probably be a long time before I see both species again in the same spring!