Nesting is slowing down, but not over yet

Back in May, my backyard pulsed with the songs of more than a dozen species of birds defending their newly established territories.

Now mornings are quiet and still. Except for house wrens and American goldfinches. My house wrens are now working on their third nest.

They start singing about 5:30 every morning. House wrens are extremely loud, territorial, and aggressive.

While most birds limit their aggression to members of their own species, house wrens are simply antisocial. Within their small territory of an acre or so, they don’t like any other birds nesting nearby.

In fact, if they find another nest too close to their own, they often visit the nest while it’s unoccupied and puncture the eggs. This kills the developing embryos and forces the “intruders” to find another nest site.

House wrens usually confine this nasty behavior to other cavity-nesters. It’s a way to “own” all the cavities within their territory. But sometimes they even puncture eggs in nests of open, cup-nesting species.

Eggs destroyed

Over the years, I’ve found punctured eggs of bluebirds, robins, phoebes, towhees, cardinals and song sparrows similarly destroyed.

I don’t know that other species avoid building nests near active house wren cavities, but perhaps they should. Destroying eggs is just one of many tactics house wrens use to gain an advantage in the intense competition for the relatively few nesting cavities available.

From an ecological standpoint, their competitive nature is to be admired. Tiny and drab, house wrens are little brown birds, but their loud, explosive, bubbly song is distinctive.

Finding nests

House wren nests are easy to recognize in a nest box. At first it seems the nest is simply a jumble of twigs. But deep in a back corner rests a tiny cup lined with rootlets, grass, leaves, animal fur and a feather or two.

Here, the female lays five to eight eggs and incubates them for 13 days. After the eggs hatch, both parents feed the nestlings for about 17 days until they are ready to fledge.

Typical broods. Two broods per season are typical, and some females raise three. The other late nester that’s just getting started is more familiar as a feeder bird. In winter, goldfinches often escape notice thanks to their drab olive plumage. But in April and May, males molt into the vivid yellow, black, and white birds many call wild canaries.

Throughout late spring and early summer, goldfinches appear as undulating lemon drops crossing the landscape. Their distinctive up-and-down flight pattern is easy to recognize.

Late nesters

Compared to most other songbirds, goldfinches nest late in the season. They usually don’t begin until early July, and if they raise two broods, they may not finish until September.

The timing of the nesting season is tied, at least in part, to the blooming of wild thistles and milkweeds. Goldfinches feast on true thistle seeds and use thistle down and milkweed silk to line their nests.

Goldfinches typically nest in forks of small trees and shrubs. If you spot a small drab olive bird in mid summer with a bill full of fluff, you’re probably watching a female goldfinch carrying nesting material.

She spends several days building the nest while her mate defends the territory by singing and occasionally chasing away intruding males. A few days after completing the nest, the female lays the first of five white eggs.

For 12 days, the female incubates her clutch faithfully. When it rains, she uses her wings as a feathered umbrella to keep the nest dry. The male visits regularly and feeds his mate mouthfuls of partly digested seeds.

Dieting needs

Unlike many birds, which switch to insect foods during the breeding season, goldfinches stick almost exclusively to a granivorous diet. They even feed their nestlings regurgitated seeds.

About ten days after hatching, the nestlings are recognizable as goldfinches. By the time the nestlings fledge a day or two later, a crust of whitewash rims the abandoned nest.

The male continues to feed the fledglings until they can fend for themselves. Other birds that sometimes nest into July and August include Carolina wrens, bluebirds, robins, and mourning doves. It’s usually September when nesting ends completely.