I've blogged on several occasions about squirrels' nests ("dreys"). At our latitude they are a prominent feature of the suburban landscape, especially when one lives next to a woods.
I've always been intrigued at how squirrels are able to tolerate arctic cold in such a porous structure, but I've been even more fascinated by the apparent sturdiness of what would appear to be a fragile construction (dead leaves and twigs).
I wrote about marcescence about seven years ago.
"Retention of dead plant organs that normally are shed." Etymology from Latin "marcere" = "to wither." ( I can't think of any related words).This year I had the opportunity to test and illustrate the process. In late summer I needed to prune some branches of a large oak tree that were shading our vegetable garden. After I clipped off a small branch, instead of tossing it on the brush pile I brought it indoors. In time the leaves duly shriveled, turning a dark green rather than brown. But they didn't fall off. Today I took it out in the back yard and held it up in front of its parent tree (photo), which dropped its leaves after a couple freezes and windy days.
"This phenomenon, when leaves fail to fall, is called marcescence. Most evident on all the oaks around the metro, it's an explainable but puzzling occurrence. At the petioles, the point of attachment to the tree, hormones flow back and forth. As the days shorten and temps fall, the amount of one in particular, auxin, is reduced. The area becomes sealed and a digestive enzyme helps to release the leaf. In fancy science talk, this all happens in the abscission zone."
After I took the photo I shook that branch vigorously. The leaves stayed attached. When I grabbed the leaves with my hand and squeezed, they were friable and crumbled to fragments. So I suppose the squirrels must use fur or other padding not only for warmth but also to prevent traumatizing the leafy branches that make up the next (as suggested by the illustration here).
Related: Word for the day: drey. And again here.