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Solving the old 'sock in the tree' mystery

Who tossed the sock into the tree?

Backyards can produce many minor mysteries, and a sock in the tree is just one. Upon closer inspection the "sweat sock" seems a little too green and not just fuzzy, but mossy. Really close inspection shows it's not a sock at all. Removing it from its resting place about eight to 10 feet up in the tree (not in the breeding season, please) reveals little except that it is woven tightly onto the branch.

The "sock" may be from eight to 14 inches long, and it feels like wool or felt. Could it be something made by an insect? Is it some kind of growth? It certainly wasn't something built by a bird. There is no opening.

Look a little closer. It's constructed of spider webs and plant fibers and decorated with moss and lichen. Investigate closer still and you should find a tiny opening high on the side about the diameter of your finger. It can be very hard to locate.

If you had been very attentive back in May, you might have noticed the tiniest of little gray birds quietly approaching and disappearing into the nest with a mouthful of minute insects. A few muffled twitters and the toe of the sock would have pulsated and shook as a family of five to seven baby birds vied with each other to be fed. The enclosed nest provides excellent protection from both predators and chill weather.

That was last May, and now the sock hangs abandoned. The skilled craftsmen were bushtits.

Bushtits are scarcely larger than a hummingbird — so small they escape the notice of most predators. As prey, one would be little more than an hors d'oeuvres. Indeed, they even look a bit like hors d'oeuvres.

A bushtit is a little ball of fluff with a toothpick-like tail. Males and females can be told apart only by the color of their eyes. The males have brown eyes; the females yellow.

Except for a brief period in April and May, you rarely see just one or a pair. Bushtits terrorize the insects of a neighborhood in roving bands of twittering fluff. The flocks can include 20 birds or more. These are family groups that remain together until the following spring when they split up to breed.

I suspect some of these gangs include several families that have joined forces. When foraging, they talk to each other endlessly. The soft, high-pitched notes blend together so you can rarely pick out the call of a single individual. The contact calls help keep the flock together as they move through the dense vegetation.

While there are many species of warblers and sparrows in every habitat of the region, there is only one kind of bushtit in all of North America. It has a few cousins in Europe and Asia, and they all build the same intricate nest.

It's easy to attract bushtits to your yard. They like nothing better than a ball of suet (without seeds) hung from a branch. Enjoy.

There! One backyard mystery solved.

Stewart Janes is a biology professor at Southern Oregon University. He can be reached at janes@sou.edu.

Michael Clark of Ashland submitted this photo of bushtits for the 2009 Oregon Outdoors Wild Bird Photo Contest (the original, of course, was in color). The birds liked his suet feeder so much they ate from his spoon. - Photo by Micahel Clark