The House Wren is a common dooryard bird in much of the Western Hemisphere, but it is just as
comfortable in human-free environments, such as the aspen woodland in which I found these two singers (one above, one below).
Male wrens are avid nest-builders and House Wrens are the terrors of the guild of secondary-cavity-nesters.
They take over cavities from other species, piercing eggs with their pointed beaks and dumping them outside.
They fill the entire cavity, or nest box, with twigs, as though to build a domed nest within a cavity. This mass of
material makes it difficult for another, earlier-nesting species to clear the cavity and use it for a normal cup nest of
grass. House Wrens did not occur at Cottonwood Gulch, where I studied Mountain Chickadees nesting in boxes,
so I don't know how the two interact. Chickadees are pretty pugnacious. I did notice that Violet-green Swallows
often used the chickadee boxes after the young chickadees had fledged. I wonder if this late-nesting habit
was forced on them by House Wrens. Both the swallows and wrens use cavities, and both are very common in
aspen stands. Just a hypothesis.
What do we mean by "Northern" House Wren. This refers to the House Wrens nesting in Canada and most of the U.S.
The Brown-throated form takes over in southeastern Arizona and occupies the highlands from there to the Isthmus of Tehuantepec.
After that it's the Southern House Wren. Serveral islands also have their own form of House Wren. And, the genus
Troglodytes has spawned the Winter Wren complex and several other species. It's a pretty successful lineage.