Freezing Frogs

View of the Wetland with Ice on Plants and Trees, 3/15/21

Overnight the temperature plummeted and today has been hovering just above freezing. During the two hours I was visiting the wetland, the temperature warmed from 33F to 36F with the wind chill about 10 degrees colder.  The water temperature when I arrived was 42F. Not surprisingly, in contrast to all my other visits over the past two weeks, there was complete silence when I arrived. The silence was interrupted briefly by the honking of a couple of geese who took off as I approached the pond (is there a pair thinking of setting up house at the wetland this year?).  Eventually there were brief bouts of one or two spring peepers making a brave attempt to attract a mate, but these never lasted more than a couple of minutes with no more than three frogs joining in at the most, long periods of silence in between.

I was dressed in two or three layers but still cold. The frogs, of course, were completely exposed to the temperature around them and unlike us, do not generate their own body heat. This means that their body temperatures are very close to the same as their surroundings. How do they survive cold snaps like this?  Or for that matter, how do they survive our midwestern winters?

The two frog species we've met so far at the wetland are the spring peepers and the boreal chorus frogs. These species are related and both spend their winters tucked into leaf litter, under loose bark on trees or otherwise sheltered somewhere. Over the winter, both species are able to survive freezing temperatures, even though their bodies may freeze, by accumulating sugars inside their cells which act as a kind of antifreeze to prevent ice from forming in the cells, which would destroy them. Ice that forms inside their bodies when they freeze forms between cells. The sugars they accumulate in their cells also serves to provide the very low energy they need to maintain life while their bodies are otherwise shut down. Their hearts even stop beating! 

Apparently this process takes place on an "as-needed" basis, so my guess is that if the temperature today had dropped below freezing it would have kicked in if needed. I didn't manage to actually see any frogs today during my visit, but the fact that some were calling sporadically would indicate that things hadn't gotten to the point of them freezing, and bear in mind that the water temperature was still a "warm" 42F (though we humans would survive at best 1 to 3 hours in water that cold).

Here are a couple of the better articles I've found online on the subject of freezing frogs:

Note: ignore the frog photo at the head of the second article -- it is not any of the five frog species mentioned in the article, or even a frog native to North America! Also, although the frog featured in the description of freezing is the wood frog (which has not been found at Homer Lake, but does occur in Vermilion County), the description is relevant to the spring peeper and boreal chorus frog as well.

Comments

Post a Comment

Popular posts from this blog

Images of Fall and Farewell!

Image
Here are five images of the wetland captured today (11/11/21). The Fall beauty of the wetland speaks for itself.  I hope you enjoy the Fall Photos! Most of the plants and animals are transitioning to a season of rest, and I am as well. Between March 1 and September 30th this year I spent over 200 hours at the wetland and many more hours working on my photos, videos and blog posts. I've enjoyed just about every minute of it and have learned a lot, but it's time for a change. My hope is that this blog has incited curiosity and stirred up wonder for all who've read some of the posts. And of course the blog will remain as a resource for all who are interested in exploring more of the wonders of the wetland. Spoiler Alert: I've been in discussion with the folks at the Homer Lake Interpretive Center and the current plan is for me to collaborate with them on an interpretive display about the wetland coming probably in April 2023 to be displayed in the Interpretive Cen...
Read more

Fairy Shrimp

Image
Fairy Shrimp from the Homer Lake Wetland Although these creatures look like concept drawings for characters in a yet-to-come Star Wars movie, they are actually small fresh-water crustaceans (think crabs, lobsters and shrimp) that inhabit ephemeral (temporary) ponds. You may rightly wonder how a fully aquatic animal such as the fairy shrimp survives from year to year in ponds that dry up completely most years. It is, after all, the fact that they dry up completely on a regular basis that makes them unsuitable habitat for fish and it is the absence of fish that makes such ponds particularly attractive for many other types of animals such as spring peepers, chorus frogs and the fairy shrimp.  So how do fairy shrimp survive when there is no water?  Female fairy shrimp lay two types of eggs. One type has a thin shell and will hatch the same season that it is laid. The other type has a much tougher outer covering and will not hatch until the pond has dried out and then has wate...
Read more

Nothing Says Fall Like a Blue-Faced Meadowhawk

Image
  Blue-Faced Meadowhawk at the Homer Lake Wetland, September 29, 2021 If you take a walk in the area where the wetland water used to be, you'll see dozens of these guys perched in the vegetation or chasing each other around. These are male blue-faced meadowhawks and they're defending good positions for when the females show up. There is no longer any standing water in the wetland, but several meadowhawk species have the strategy of dropping their eggs in areas they expect there to be water come late Fall or early Spring. In addition to ephemeral pools of water being fishless, already a great advantage for the many species that prefer ephemerals, I think the meadowhawk strategy of dropping eggs in the fall where there is no water may also give them a competitive advantage over other dragonfly species. Meadowhawk species are smallish dragonflies, so jumpstarting the growth of their naiads as soon as there is water in the wetland again and before other dragonflies are around...
Read more