A field guide to nestlings

Checking a nestbox

Yesterday afternoon Dan and I went out with our cordless drill to check the nestboxes in the fields behind the house here. There were ten nextboxes in these meadows, and another seven or eight at the 100-acre woods. We didn’t have time to get over to the latter group. One of the ten here had come unattached at one end and was hanging sideways. I wasn’t too surprised at this as they do seem to be fairly old boxes, but I hadn’t been expecting it. Fortunately, this seems to have happened before anyone got around to using it, but I intend to replace a few of the worst boxes and make sure the others are firmly secured so it won’t happen again.

The remaining nine boxes were all occupied, however. And all of the occupants were birds. This was gratifying for me, since I’d gone to the trouble of cleaning them all out back in March. It was fun to open each up and see who had made it home.

House Wren nestling

The first box we opened was the one that the bluebirds had nested in last summer. We had seen the bluebirds checking it out early this spring, but they had disappeared from that field soon after, and seemed to be hanging about the fields farther back. When we took the door of the box, it was apparent why they’d decided to leave: the box had been taken over by House Wrens. At the bottom of the box was the grassy base of a bluebird nest, and on top of that were the thick twigs that the wrens prefer for their foundation.

The nestlings we found yesterday were all at different developmental stages. This one is about halfway through growing. Its eyes are opened and the feathers are just starting to burst from their waxy sheaths. When I first lifted it out of the box the blue-gray sheen from the sheaths made me initially think “bluebird!” before I realized it didn’t see quite right, and noticed the brown fuzz of the emerging feathers. He’s still naked enough that you can see the big hole that is his ear, behind and about the same size as his eye. Once all the feathers are grown out these holes will be protected by a handful of special feathers with a low density of barbs that allow more sound to pass through.

Four of the nine boxes contained House Wren families. I knew about two of them, the two boxes nearest the house, as I’d heard the two males countersinging from time to time, but I didn’t realize that we actually had four pairs in the area. Most surprising was that the distance between the two farthest apart was only about 330m (1090 ft); four pairs crammed into less than four acres, food must be abundant here. All four boxes had baby wrens, some younger than others.

Tree Swallow nestling

There were two boxes with Tree Swallows nesting in them. The nestlings in the first box were younger than those in the second, and the adults were using a box that had been used by House Wrens last year. Even at this young age you can really see the difference in shape between the different species. The Tree Swallows are noticeably longer, with stubbier beaks, than the House Wrens.

Tree Swallow nestling

The young swallows in the second box were much nearer to fledging, perhaps only a few days away. This one sat alertly but quietly while I took its photo, but this was probably the last day on which it would; any older and it would likely try to make a break for it.

These guys were in last year’s chickadee box. We found a box that had housed chickadees this year, too, though I didn’t get any photos as the young seemed to have already fledged (perhaps they’re the ones I’ve been hearing begging for food in the trees around the house just recently). This year’s chickadees were in a box used by wrens last year. It’s interesting to note how the species all seem to move around, like they’re playing musical nestboxes. I would have thought that the “microhabitat” around each of the boxes would have more of an influence on who chose what box.

Bluebird chicks in nest

We had a sense of which areas the bluebirds might be in, but the first one took us a bit by surprise, as I’d actually thought this box was being used by Tree Swallows, and the one around the corner, which it turns out is being used by swallows, was the one I thought the bluebirds were in. As the chicks get larger it starts to be quite a tight fit in the little nest, and when you look in often all you see is a big mound of feathery bodies. It makes it hard to count how many individuals there are, especially once they’re past the stage of lifting their head to beg for food at any sign of movement. It looks to me like there might be five bluebirds in this box, but we didn’t lift them all out to check.

Eastern Bluebird nestling

The bluebirds are easy to identify because of the blue feathers, and the speckling on the back and shoulders that are characteristic of the thrush family (robins and the spot-breasted thrushes also show these speckles). The male chicks have got these lovely blue tail and wing feathers. Feathers of female chicks will be more grayish, perhaps with just a tinge of blue. I only removed the one chick, above, which happened to be a male, and I’m not sure what the ratio of males to females in the nest was, though I can see at least two males in the nest photo above.

Bluebird eggs in nest

The very last nestbox, at the very back of the property, was the second bluebird. While every other nest we’d check had nestlings (except the chickadee, which was empty), this last nest still contained eggs, the smooth blue-green that’s typical of thrushes (including robins). Tree Swallows have white eggs, and House Wrens speckly brown ones. The grassy lining here is typical of our bluebirds, too.

It’s great to see all the nestboxes being used, and all of the broods doing so well. On our next sunny day I’ll make a trip around to the 100-acre woods and see what’s happening over there, too.