A second brood gives short-lived house wrens a greater shot at survival

The house wrens that chose our yard for nesting this spring furnished a bungalow.

In early July, for their second nest, they pushed and pulled sticks into what has to be considered a mansion.

The photo tells the story. The large box is the new nest site. In the background to the right is the round PVC box used for nest No. 1.

The small box has a floor 4 inches in diameter, about 12 square inches. From entry to box bottom is 5 inches. Living space then is 60 cubic inches. In that space the wren pair raised seven young.

The large box, meant for great crested flycatchers, has dimensions of 6 by 6 by 8, 288 cubic inches, almost five times as large. That doesn't mean a larger clutch of eggs. Seven or eight is average for house wrens, nine or 10 unusual.

A second nesting, however, likely will be four to six eggs. The female lays one egg per day, usually first thing in the morning. The eggs hatch in 12 days, all of them within about 24 hours.

This information comes from the monograph on house wrens found in "The Birds of North America" printed series. (See allaboutbirds.org/guide/search.)

Our wrens, annual nesters in the yard, choose our more conventional offerings — actual nesting boxes.

The male is first to arrive, ours singing nonstop for days before luring a mate. Between songs the male filled one PVC nest box with sticks, another partially so.

Nest location choice and prep is part of his allure, proof of his worthiness as a mate. The female takes charge when she arrives.

Both birds here worked full time on the second nest, a stick or twig per minute at times, one bird entering the nest as the other left.

Assuming the birds are successful with the second brood, a clutch of five eggs will give them 12 for this breeding season, a clue to their potential longevity.

"In fact," according to ABC, "once most birds develop their adult plumage, they essentially become impossible to age."

We do know, however, that larger species live longer than smaller species, giving bigger birds more chances at reproduction. Small birds make the reproduction numbers work with earlier maturity and larger families.

Lifespan can be determined by marking individuals, for birds usually a metal band on a leg (banding), recording date of that action, then hoping for eventual retrieval of that information.

We've had nesting house wrens every year we've been here, as far as I remember. Some of those must have been returnees, others attracted by good wren habitat (woodsy, brushy).

I have many photos of wrens for the same reason there is extensive research literature about the species. Nesting in a box or a cavity, wrens are easy to observe.