Dear Bird Folks,
I saw a wren in my yard last week and I want to put out a nest box. Is there a special size box that wrens like?
– Wally, Wellfleet
Hmmmm, Wally from Wellfleet, eh? You don’t write kids books, do you? It’s cool that you saw a wren, but we need to know what kind of wren you saw. There are two kinds of wrens that nest in boxes on the Cape, the house wren and the Carolina wren. You’ll have to look them up in your bird book. I’m not going to describe the field marks of both or this answer will run long and ol’ Jim from Chatham will start to freak out again.
Wrens aren’t all that fussy, they’ll nest in just about any cavity they can find. Besides birdhouses, they will use woodpecker holes, mailboxes, old drain pipes, clothespin baskets (remember those?) and I have even heard of them building nests in old cow skulls. So if your house is full of cow skulls, put some of them outside and you can save yourself the price of buying a new nest box.
Although both wrens use birdhouses, they can’t use the same size house. The house wren is a much smaller wren and only needs a box with a 1 inch opening. There is no way a Carolina wren could fit in that tiny hole. So if you are sure that you have house wrens, and want to keep all other birds out, get yourself a birdhouse with a one inch hole.
However, my guess is that you have a Carolina wren in your yard. Although not as easily attracted to birdhouses, Carolinas are the more common of the two wrens on the Outer Cape. They are a bit bigger, thus need a bigger entrance hole (I figured that out for myself). For Carolina wrens, choose a box with a 1 1/2 inch hole. They sometimes can squeeze in holes a tad smaller, but why make them join Weight Watchers just for you.