Scheduled post: Frogs in the garden

Leopard Frog

Over the weekend I spotted a couple of frogs hanging out in my garden, enjoying the flowers. The first was this huge Leopard Frog, who seemed to take a liking to the Love-Lies-Bleeding. Consider that that’s a 6-inch diameter pot. Leopard Frogs are one of the more common frogs of ponds and wetlands through much of southern Ontario, so I’d seen many, but this was easily the largest one I’d encountered. I saw him in that pot on three occasions over as many days; he was there often enough to flatten out a depression in the soil surface where he sat.

Wood Frog

The other was this Wood Frog, who I disturbed when I went to sort through my moth trap one morning. I wrote about Wood Frogs last spring after an encounter with one who came to my moth sheet one night, and also posted about mating Wood Frogs I discovered this spring.


Wood frog love

Wood Frogs

On Sunday, Dan and I took Raven and went up the road a little ways to a plot of crown land. There are a few such pieces, owned by the government and open to public recreation, but we only just recently found out about them, when Dan was doing background research for his new Frontenac Bird Studies program (incidentally now starting to gear up). Dan intends to install some his monitoring programs on these crown land parcels, and on Sunday the outing was dual purpose: to burn some puppy energy, and to scout the land a bit further for suitable spots.

As we neared the back boundary of the crown land we passed a pond from which I could hear frogs croaking. Dan offered to take Raven and carry on to the end, and then come back to get me on his way back. In the meantime, I’d scout the pond and see if I might be lucky enough to spot a couple of the noise-makers. Sounded good to me, I really wanted to check out some of the spring amphibians, but last thing I needed was a water-loving dog splashing around and disturbing everything. If I was by myself I might have her sit-stay, which she’s pretty good with as long as you don’t go far or keep her sitting long, but really this arrangement was better for everyone.

I followed the croaks to the back of the pond where it didn’t take long to spot a disturbance in the water. Drawing closer, it appeared to be a female with suitors. Drawing closer still, there appeared to be four love-struck males surrounding her.

Wood Frogs

The one that was swimming around the bunch buggered off when I got up next to them, but the other three had fought hard for their respective positions and weren’t about to relenquish them that quickly. That poor female could barely move, and I was started to wonder if it was possible for amorous male frogs to choked a female to death. Her strange red colour seemed odd, too. I was pretty sure that these were Wood Frogs, even though they didn’t show the typical dark masks the species usually does; I couldn’t come up with any other species might even be possibilities. But the reddish was a colour I hadn’t ever seen among Wood Frogs, so I wondered if maybe there was a species I didn’t know of around here. Or maybe it was just all the blood rushing to her head.

Wood Frogs

They were close enough to the shore that I could scoop them up with one hand, which I did just to make sure that the female really was still alive – she was. The third male took off when I disturbed them, but the other two still hung tight. Male frogs grip the females in a position called amplexus – Latin for “embrace”, even though is seems more like chokehold. Typically, if there’s just one male involved, Wood Frogs (and other “true” frogs, tree frogs, and Bufo toads) grasp the female from behind around her armpits. Obviously these boys had skipped that sex ed class.

The embrace can be iron-strong, seemingly locked in place, and if a love-blind male accidentally hooks up with the wrong species, the unwitting object of his affection may have a tough time escaping. The “lock” mechanism is a swollen pad, called nuptial pads, along each of the male’s “thumbs”. The pad is actually a gland that enlarges during breeding season and secretes a sticky glue-like mucous. The mucous, in combination with a rough pad surface, keeps the frog’s arms locked in place around the female.

Wood Frogs

This was another trio I found just a bit further down the shore. At least one of these guys knows what he’s doing. The female was that same weird shade of red. Apparently Wood Frogs will swim around in amplexus for an hour or more, but the actual egg-laying only takes about half an hour. The female lays her eggs in a large gelatinous mass, and the male releases his sperm over the eggs as she lays them. I looked around the edges of the pool where the frogs were, but saw no evidence of eggs anywhere. I must have found them in the early stages. The pond, apparently a vernal pond, had very little vegetation in it, so I hope they were able to find a suitable place to lay their eggs.

Wood Frogs

When I slipped the frogs back into the water, one male kicked off, propelling the whole group away from me toward the pond bottom. They weren’t very efficient swimmers in this state, clumsy and uncoordinated, and I mused how they would be easy pickings should something hungry come along. Good thing there weren’t any herons patrolling the shores of this pond. I guess, even though they’re somewhat vulnerable for an hour or so during the process, the odds of a predator happening across them during that period is pretty slim and most of them get the job done with no more threat than the occasional passing naturalist.

The death-defying frog

Wood frog

Last week, while out checking my moth sheet at my parents’, a frog came up and found me. He hopped right up and on to the white sheet, where I couldn’t miss him. Perhaps he was jealous of all the attention the Gray Treefrog got a few weeks earlier, but he certainly seemed to want his own feature story. What could I do but oblige?

He was small, and his colours seemed underdeveloped, which made me wonder if he was still an immature, not too far removed from his water-loving days. Still, despite the indistinct markings, they were clear enough for me to confidently identify him as a Wood Frog, Rana sylvatica. Adult Wood Frogs will have a dark chocolate-coloured mask, which has contributed to their colloquial names of bandit frog or masked frog, though these names are rarely used. They’re the only species in eastern North America with this facial marking. The top of their eyeball is golden while the bottom is dark, blending in with the mask pattern that crosses it. They have two lines that run laterally down the length of their back, a white “moustache” along their upper lip, and a small dark patch at the front of each shoulder, but generally otherwise they’re brown and fairly nondescript. If the mask isn’t well-developed, as in this individual, they’re not very distinctive.

They vary in size according to age and sex. Males are smaller than females, and the small size of this little individual may also have meant it was a male. In breeding season the males will develop a swollen “thumb” that they use in gripping the female during mating, but it wouldn’t be apparent at this time of year. Wood Frogs may live up to 4 or more years; males begin breeding their first summer as an adult, but a female doesn’t breed until her second.

Wood frog

Wood frogs are North America’s most northern-occurring species, and the only one found above the Arctic Circle. They range from coast to coast in Canada, found from the Aleutian Islands in Alaska, through northern and interior British Columbia and the three territories, east to Labrador and the Maritimes. In Ontario, they’re found right up to the Hudson Bay coast. They are also Canada’s most wide-ranging species. They’re less widespread in the states, found mostly in the northeast, with small local populations in Colorado and Wyoming.

Part of the reason for this distribution is their choice of habitat. They’re found in the boreal forest and the deciduous forests of the northeast. Although individuals may move up to a kilometer during their summer foraging activities, they’re rarely found far from water. More specifically, they must be near vernal pools, small ponds and wet depressions that dry up partially or completely in the summer, their primary breeding habitat.

Wood frog

Even before the Spring Peepers start peeping, the Wood Frogs emerge and congregate at vernal pools to breed. They are quite often the first frogs heard calling just as spring starts to arrive. Males will gather at the breeding site, calling loudly and sounding a little like a duck quacking. However, they only call until the females arrive, which may be right away or up to two weeks later, after which they’re infrequently heard.

Females may lay up to 2000 or more eggs, secured to the base of a submerged shrub or other vegetation. Eggs are laid in a large mass, and later females may add their eggs to the initial groups. Laying eggs together like this creates a large, dark ball, which warms up in sunlight more quickly than individual or a string of eggs would, important in early spring when the water can be very cold. Mating takes place in early to mid-April, as soon as the pond’s water is accessible. Because the pond is likely to completely dry up in the heat of summer, it is mandatory that the frogs’ tadpoles get as early a start on life as possible.

Although the tadpoles in vernal pools are under constant threat of their habitat drying up before they’re ready to leave, they’re also protected from fish and many other predators found in larger water bodies that can’t tolerate the drying out. It takes a tadpole anywhere from about 45 to 85 days to go from egg to frog, with the wide range depending largely on water temperature. Warm conditions can speed up the process considerably (which is good, because warm conditions can also speed evaporation). Usually the tadpoles are out well before the water dries up completely.

Wood frog

Newly-metamorphosed froglets and adult frogs that have finished breeding will spend the rest of the summer hopping around the woods surrounding the vernal pools, foraging on typical frog fare: crickets, earthworms, slugs, spiders, beetles, and whatever other similarly-sized invertebrates they happen to come across. During this period they may roam hundreds of meters from their home pond, and about 20% of young froglets will disperse to other nearby ponds, maintaining gene flow.

When fall rolls around, the frogs return to the upland forest area near their pond and start preparing for the winter. Part of this involves converting the glycogen in their bodies into glucose. Glucose acts as a sort of natural “antifreeze”, preventing the fluid inside their cells from developing ice crystals which will puncture the cell walls. The frog then buries down under the leaf litter, but, unlike many other frogs that will burrow down below the frost line, the Wood Frog remains near the surface. Slowly as the weather turns cold it stops breathing, its heart stops beating, and its brain shuts down – for all intents and purposes, becoming clinically dead. The internal (but extracellular) fluids of the frog freeze almost solid. The frog remains protected from the elements by the surrounding insulation of the leaf litter and snow, but still able to withstand ambient temperatures of as low as -6 C (21 F).

Wood frog

With the melting of the snow and the warming weather, the process reverses. The sun’s warm rays hit the dark leaf litter, warming the ground and the frog hidden within it. Slowly the frog’s internal fluids melt to become liquid again. About an hour later its heart then begins beating again, and it starts to breath. Brain function returns to normal, and the frog’s body begins to convert the glucose back to glycogen again. Within a day the frog can resume normal activity.

Several species of frogs have evolved the ability to survive such winter freezing, nearly all being early spring breeders. Spring Peepers, Boreal Chorus Frogs and Gray Treefrogs all freeze during the winter. The advantage to such an adaptation is that it allows the adults to start breeding as soon as temperatures rise above freezing. Virtually all of these species are terrestrial forest species that take advantage of vernal pools and need to lay their eggs as early as possible.

Naturally, scientists are very interested in this amazing ability, since it would have application in tissue and organ preservation, and the practice of cryonics (freezing whole living organisms to be resuscitated later). Given that a frog may live to age four or more, it may go through this freezing process three or more times in its life. Check out this documentary clip (from YouTube) to watch a frozen frog come back to life: