The changing natural world at our doorsteps | Illustration and text by Patterson Clark
April 5, 2011
House wrens: Success in the city
House wrens will soon arrive from as far away as Central America. As they fill the spring air with effervescent song, they'll also be aggressively pursuing suitable nesting cavities, sometimes destroying the eggs and nests of other small birds.
As they hunt for food and collect nesting material, house wrens find spider egg sacs, which they add to the nest. When spiders hatch, they devour mites and other nest parasites.
House for wrent
If you like tiny, chatty neighbors, you can build a home that will attract them. A single plank of lumber, 1" x 6" x 48", can be cut and assembled into a house-wren home. The box should be mounted to a wall or post six to 10 feet off the ground.
The benefits and perils of suburban nesting
A house wren born in a city nest box stands
a better chance of fledging (flying the nest) than do catbirds, mockingbirds, robins and cardinals, which build open-cup nests. A wren's cavity nest, with its small entrance, provides more protection from crows and
jays, the primary nest predators of the Washington area.
Suburban bird nests tend to be less bothered by predators than are rural nests, which fall prey more often to small rodents. But while suburban wren babies are more likely to
fledge than rural wrens, they develop more slowly and are less robust, perhaps because their insect food is of poorer quality.
For a suburban mother wren, more time spent searching for food means less time brooding (warming) her chicks, causing them to use up more of their energy to stay warm while she's away.
And once they leave the nest, smaller, weaker suburban wrens are likely to face an environment more challenging than in the country: more pollution, more noise, more cats.
SOURCES: Cornell Laboratory of Ornithology; "Reproductive Success of House Wrens in Suburban and Rural Landscapes," The Wilson Journal of Ornithology; "Quantifying avian nest survival along an urbanization gradient using citizen- and scientist-generated data," Ecological Applications; Plans redrawn from "Woodcrafting for Wildlife," by Jerry Hassinger