It’s mid-October and most of our summer wildlife has disappeared for the winter: birds south, insects dead or tucked away, herpetiles and cold-sensitive mammals holed up. We still get the occasional warm day, though; Thanksgiving weekend, for instance, was beautiful with highs in the mid-20s C (mid-70s F). Some hibernators, snakes in particular, will take advantage of these lovely afternoons to soak up a last few rays.
It was on one such day that I came across this Northern Leopard Frog (Rana pipiens). I nearly stepped on him, in fact. He was in a hollow of moss, back in our little bog-fen. I must admit, I was rather surprised to see him so late; aside from one or two lonely Spring Peepers peeping in the nearby swamps, it’s been weeks since I saw a frog. I’d sort of forgotten about them, assumed they were all snugged away for the winter. It was a nice day, but it still wasn’t exceptionally warm, particularly in the shaded dampness of the bog-fen. The frog, being an exotherm, wasn’t feeling his most chipper self as a result. He flinched a bit as I reached down, but didn’t make any effort to leap away. When I gently picked him up he sat calmly, his throat puffing as he breathed, hunched close to my hand.
According to this site, Northern Leopard Frogs will start to head for hibernation sites at the bottom of ponds or lake edges once air temperatures fall below 2°C (36°F)… though it doesn’t specify daytime or nighttime temps, or whether those temps need to be sustained. Definitely we’ve already had quite a number of nights that have gotten that low, at the end of September. Our daytime highs have for the most part remained in the double-digits Celsius, though.
That website happens to be one for the Canadian Species At Risk registry; I was a little surprised to see that the Northern Leopard Frog had a page there. The species is certainly no less abundant than any of our other frogs, either here or where I grew up, in the Toronto area. It turned out the SAR registry listing was for the western boreal and prairie populations, which have suffered noticeable and serious declines since the 1970s. Although the reasons for the decline are not clear and probably include several different contributing factors, one of the key players is thought to be the acid rain of the 70s, 80s and 90s, the effects of which were especially pronounced in boreal regions where the granite bedrock was unable to neutralize the acidity of the rain (compared to the limestone bedrock south of the Canadian Shield, which is basic and therefore could to some extent). In the prairies, it’s more likely that habitat loss has been the largest factor in their decline.