Why write about pinkletinks — also known as spring peepers everywhere but the Vineyard — at this time of the year? We are all preparing for winter by getting out our winter clothes, shutting storm windows and turning on the heat. Frogs cannot do those things, but they have other ways of surviving the winter.
After the spring chorus ends, the pinkletinks abandon the ponds and migrate to nearby uplands. There they establish territories that may be 18 feet in diameter. They spend a lot of time in the leaf litter or under logs lying on the ground, but they are also adept climbers since each toe has a terminal pad that secretes fluid to help them hold onto vertical surfaces. I have observed them climbing houses and windows.
Scientists report these one inch-long tree frogs establish their winter territories up to 1,000 feet from their breeding ponds, but they have been calling near my house since September, and my house is about 1,500 feet from the closest breeding pond.
Few people recognize the autumnal call of pinkletinks, although they have been calling since September. At this time of the year we do not hear the familiar spring chorus. Now only one frog is calling at a time, so we hear a single high-pitched note that has been compared to an insect chirp or a baby chicken’s peep. Their call is not as reliable as the spring chorus, as it is not heard every day. But it is heard occasionally during the daytime, repeated up to several times per minute. During last year’s winter that never really came, it was so mild that I heard pinkletinks calling every month. Although the call is hard to locate, I am sure that they are often calling from the tops of trees.
So how do these adult tree frogs survive the freezing temperatures of our normal winter? They protect themselves from some of the cold weather by burying into the leaf litter. This can protect them for most of the winter, except for the prolonged cold snaps when the temperature stays below freezing and the upper layers of the soil freeze.
These frogs survive our colder weather by freezing. Several species of frogs (not just pinkletinks) have been found as frozen as an ice cube, only to revive when they thaw out!
When they start to freeze, their bodies produces sugars and alcohols up to 100 times their normal concentrations. These chemicals are distributed throughout as their bodies start to freeze. These extra chemicals reduce the water content of their major organs by up to 50 per cent. The water moves out of the organs and into the body cavities between the major organs, where it then freezes without damaging any internal organs. Their entire body stops functioning during such freezing weather, but their heart and other organs resume normal chemistry and functions uninjured when they thaw out. This amazing recovery takes more time when the frogs remain frozen for longer periods of time.
This antifreeze technique works for temperatures down to 18 degrees Fahrenheit. Of course, our air temperatures can get much colder than that, but most of these frogs will be buried in the leaf litter and soil. The temperatures there, even a short distance underground, are much more constant.
If soil temperatures fell below 18 degrees Fahrenheit, we would not have pinkletinks.
Robert Culbert leads guided birding tours (www.facebook.com/robert.culbert.58) and is an ecological consultant living in Vineyard Haven.