The nuthatch hole.
4:22. It seemed a little early for nuthatch bedtime. A full half-hour before sunset, and an hour before real darkness set in. So I decided to sit down on the river ice below the small knothole it had disappeared into and watch. I eyed the hole as steadily as other distractions would allow to see if it was in there for good, or just for a visit.
4:30. A red-bellied woodpecker clucked restlessly from branch to branch, checking out his own potential accommodations...4:40. A muskrat swam by...
4:44. Having almost forgotten about the sleeping nuthatch, I heard a scuffle overhead. Looking up I see two nuthatches tumbling out of the sky toward me, apparently having fallen straight out of the knothole. An interloper! The two fought it out in a squeaking blur of feathers for a few seconds until one (I imagine it to be the original inhabitant) emerged as the victor and returned to the hole. So that's why he went to bed so early. Possession is nine-tenths of tree-cavity law, or at least pretty important. Essentially, this was prime nuthatch real estate.
The nuthatch hole from a distance.
This made me think about all the other birds that sleep in holes, and how finding a good hole with all that competition can't be easy. In fact, it seems like most of the birds in the woods right now are "cavity nesters," which means they also generally sleep in knotholes, woodpecker holes, hollowed out branch stubs, nooks, birdhouses or whatever enclosed space is available. The titmouse, chickadee, nuthatch, bluebird, brown creeper, Carolina wren, 6 woodpeckers, and a screech owl: that's a lot of competition!
A titmouse finds shelter in a hollow silver maple branch (not a recent photo).
I would bet that for all of these species, finding a hole at night in winter is a primary concern, almost as big as finding food. Especially when it is 5 degrees and windy out. This is supported by the fact that a good hole seems to be worth fighting for. Remember the nuthatches? And last month the Cape May Bird Observatory posted an account (click and scroll down) of a sapsucker that wouldn't let a poor brown creeper sleep in the same tree nook with him! You would think that it would only make it warmer. (Bluebirds are known to sleep 10 to a box in winter for this very reason.) Maybe the sapsucker just didn't trust that strange-looking, pointy-beaked creeper - a case of speciesism. Or maybe you need just need to be previously acquainted! In the case of the nuthatches, maybe the interloper wasn't a sibling or close relative, but was from another tribe.
Or maybe there just wasn't enough room.