I had left several nest boxes uncleaned because some deer mice still appeared to be raising young when I had made my end-of-season rounds in early October. (We have very few predators in our area, so our boxes are all on trees.) When I went back to clean them out a few weeks later, I inadvertently opened a box I had already cleaned out. I found what must be a box that some bird(s) is using for roosting. This box was clean as a whistle in early October. Now, it has numerous white poops (technical term used by wildlife rehabbers ;-)), which tells me it’s a bird rather than one of our small mammals (whose poops would be dark). Clumps of what look and feel like rabbit fur line the bottom edge. (The positioning of the fur reminded me of caulking cracks in a house to keep the winter winds out.) I don’t believe I’ve seen anything like this when I’ve done a beginning-of-season box check in mid-March. We recently had a couple of early-season October snows; one of which was about 6″ and one, about 18″. Could those have had anything to do with this construction? The only cavity nesters we have around here now are our little ones: White-breasted Nuthatches, Juniper Titmice, and Mountain Chickadees. I don’t know for sure, but I’m guessing it’s a White-breasted Nuthatch. When nest-building begins, the main way I identify a nuthatch nest is by the clumps of fur that I see as one of the last layers of the nest. Chickadees and titmice are much more prone to use strands of hair.
Another surprise awaited me when I opened a different box in October to clean it out. That time of year, I occasionally come across a deer mouse still raising a family. I can recognize their nests quite easily; they reach up almost to the bottom of the entrance hole and they are made of very fine juniper strips—much finer than chipmunks. (You can see some photos of these 2 nests here.) I almost never can see a deer mouse in the nest because she burrows deep inside. If she’s there; I can usually tell when I slip the paint scraper under the nest to lift the nest slightly; and notice that it’s inordinately heavy for an empty nest. A tiny squeak usually clinches the ID and I close the box and move on. But in this box, I first saw a rather low nest, with strips of dried vegetation rather than juniper bark. While I was studying the nest, I realized that something was also studying me—2 small mammals with HUGE ears! I quickly snapped a couple of photos, closed the box, and headed back to the house to figure out what they were. Definitely not deer mice, that’s for sure. I’m guessing that they were pinyon mice—the size and coloring match sources I’ve read and all of point out that the ears are much larger than those of a deer mouse (1″ vs. 1/2″). They seemed much less skittish than the deer mice I’ve encountered—they didn’t seem particularly perturbed by my opening the box.