Multi-brood birds

“Do phoebes raise more than one brood a season? asks Flo Vannoni of Redding.

“A pair of phoebes nested over our sliding door and succeeded in fledging three babies,” she writes. “The babies left the nest about one week ago and since then, we had not seen parents or babies. Today one of the parents returned to where the nest had been – I had removed it. Is it possible they would start another nest?”

Many species have more than one brood in a season, as Mary Walsh of Ridgefield – who sent the accompanying shot of a second-brood bluebird chick – can attest.

“The baby bluebirds fledged last week from a nesting box on my property,” Mary wrote July 14. “It is the second brood this summer.

“I found one baby hiding out on the running board of my Sequoia. As I tiptoed within a few feet, the baby bluebird hopped away. It appeared to be struggling to fly… Mom and Dad were in the trees chirping away. I had to leave and he was gone when I returned home. I hope he took flight.”

Flo wondered whether her phoebes would start another nest. They probably would, and perhaps in the same location since they would likely have used the old nest a second time.

Eastern Phoebes are very loyal to nesting location. They not only use the same nest for their two broods in a season, but also tend to re-use it for several years. That is relatively unusual among songbirds, most of whom build new nests every year. Phoebes simply make repairs and spruce up the previous year’s nest – “waste not, want not” is apparently the motto of this avian recycler.

For many songbirds, whose offspring hatch relatively quickly and don’t take long to fledge, having two broods in a season in this part of the country is normal. There is plenty of time to raise two families, and then fatten up for the migration south or, for many year-round species, to stock up on food for the winter.

Studies have found that northern birds of a given species tend to have fewer broods than southern birds, yet all produce around the same number of young per season.

In the North, for instance, Eastern Bluebirds typically have two broods. In the South, because the warm, insect-filled season is longer, bluebirds often have three broods.

Nevertheless, both northern and southern bluebirds produce about the same number of offspring per season because bluebirds in the North lay more eggs per brood than bluebirds in the South. A pair of Connecticut bluebirds might have two nestings, each with five babies, while a North Carolina bluebird couple might have three nestings with three eggs each. The result is about the same.

Did the southern birds work harder? They had more nestings, but fewer mouths to feed at each. Moreover, they probably did not migrate as far, if at all, to set up home.

(Photo of bluebird parent arriving with food for babies is by Kevin M. Doyle.)

Funky nests

You can find them in hanging flower baskets, an old boot, a garage shelf, or under a bridge -- birds build nests in the strangest places, note the folks at Cornell Lab of Ornithology. As part of their Celebrate Urban Birds project, the Lab is sponsoring “Funky Nests in Funky Places!” competition.

Celebrate Urban Birds is a free, year-round citizen-science project, focused on birds in neighborhood settings. While we are much more “suburban” than “urban,” Cornell points out, “We will gladly accept data from all locations, including suburbs, small towns, small cities, as well as large cities. It is exciting for us to receive data from a large variety of ‘Green Spaces.’”

For the Funky Nests in Funky Places challenge, the lab wants you to take photos, do a painting, write a story, or shoot a video showing a bird’s nest built in some out-of-the-way or out-of-this-world place. “When observing nests please be sure to avoid touching them or disturbing the birds,” Cornell adds.

There are prizes for the best shots, including a Leica C-Lux 3 compact camera, bird feeders, shrubs for planting, and more.

To enter, email your entry to urbanbirds@cornell.edu. Links are acceptable for videos. Write “Funky Nests” in the subject line. Include your name and mailing address. Explain why you submitted your entry -- what's the story behind it?

Deadline for entries is July 31.

Visit the Celebrate Urban Birds website, birds.cornell.edu/celebration/ for more information.

Mating matters

The season of nesting is a good time to take a look at the kinds of male-female relationships that exist in the bird world. Many birds form lifetime partnerships – though they may have quick “flings” on the side – while others mate for only short periods or have multiple mates.

Ornithologists describe three kinds of mating arrangements: monogamous, polygamous and promiscuous. In monogamous pair bonds, the birds mate for at least the breeding season, raising their young together. Ornithologist David Lack estimated that at least 90% of nest-raised birds come from monogamous pairs. So do 80% of precocial birds – those able to walk about and feed themselves shortly after birth.

In many, perhaps most cases, monogamous pairs remain mated until one of them dies. Canada Geese are among the most faithful birds, mating for as long as 20 years. Most gulls also pair for life. The Rose-breasted Grosbeaks at the left are monogamous. This system is the most efficient and effective, providing the best protection and service for the brood of nestlings.

Some birds, such as House Wrens, generally stay with one mate for only one brood. In fact, while the male is raising the first brood, the female may take off, find a new mate, and begin a second nest. Talk about energy!

In the case of polygamous pair bonds, one male or one female may have several mates. In the more common arrangement, like the harems of lore, one male has several females. This is called polygyny. Wild Turkeys, Ring-necked pheasants, grouse, Bobolinks, and Red-winged Blackbirds are polygynous. The male generally sticks with and protects his several wives and their offspring while each female takes care of raising the children. This system is more selective than one-on-one mating; The one male that is able to build a harem of several females will be stronger and perhaps healthier than the average male and will likely pass on these traits to offspring.

In a few species, the female makes use of several mates. The Spotted Sandpiper lays eggs in several nests and the males incubate them. This system, called polyandry, allows one female to produce many eggs and is useful in situations where the breeding season is short, such as in the Arctic.

Promiscuous mating occurs when two birds have sexual relations and part company. Typically, and perhaps not surprisingly, the male takes off, leaving it up to the female to raise the resulting family. The most famous practitioners of promiscuous mating are the hummingbirds and woodcocks. Dr. Steve Kress, a noted ornithologist with National Audubon, says that typically, either the brood is small, such as in hummingbirds, allowing the female to raise the chicks alone, or the offspring are precocial, as in woodcocks, able to walk and feed themselves soon after birth.

For a long time ornithologists thought that monogamous birds were totally faithful to one another. However, DNA testing and close observation have revealed that monogamous birds may have fleeting “affairs” with other partners.

Zoologist David Barash and Judith Eve Lipton reported in The Myth of Monogamy in 2001: “When it comes to actual reproduction, even bird species long considered the epitome of social monogamy, and thus previously known for their fidelity, are now being revealed as sexual adventurers. Or at least as sexually non-monogamous.” These include eagles and geese, long thought to be strictly monogamous.

Swans, doves, finches, hawks, wrens, flycatchers, thrushes, and warblers occasionally switch from monogamous to polygamous pair bonds.

What happens when a mate dies during the nesting season?

Birds that form monogamous pairs do so largely to share in the job of raising young. Nesting season is a dangerous time, full of threats to the parents as well as the eggs and nestlings. Predators, as well as disease and accidents, may kill birds, leaving a widow or widower to care for the nest. Among monogamous pairs, it’s difficult or impossible for one bird to find food and protect the nest.

Fortunately, there are what ornithologists Allan and Helen Cruickshank call “a floating population” of unmated birds that are available – even anxious – to jump in and replace missing mates.

Up on the Roof

Some wildlife has taken kindly to suburbia, delighting in man’s manipulation of the landscape. Deer and the Canada Geese like our environment so well, they’ve overpopulated into pests.

Others are more subtle at adapting. The Killdeer, a common plover that looks as if it belongs on a beach where most of its cousins live, is doing well, population surveys report. This might seem odd since Killdeer nest on the open ground, and in the suburbs, about the only open grounds are lawns and parking lots.

Killdeer will in fact nest on grassy islands in the middle of shopping center lots. If a shopper gets too close, mom or pop will stage the famous broken-wing act, fluttering along the ground to draw attention away from a well-camouflaged nest.

Many Killdeer have discovered much safer nesting grounds. The flat roofs of the shopping centers and office buildings that fill our business districts provide fine Killdeer homesites. The parents don’t have to worry about four-legged predators – or two-legged interlopers – and can concentrate on watching for the usual enemies from above, such as crows and hawks.

For the Killdeer, up on the roof can be down home.

A bird’s blessing

The American Goldfinch is a patient bird, at least when it comes to building a home and raising a family.

Each season, goldfinches are among the last of our birds to establish nests. Most others already have fledglings – you can hear them now, squeaking and whining at their parents to feed them. But goldfinches are just getting their nest work underway.

Why? The goldfinch seems to time its domestic duties to the season of the thistles, those prickly wildflowers most people hate. Early thistles are just now going to seed, producing the super-soft down that is so opposite the thorns that bedeck the plants. Goldfinches love thistle down as a material for lining their nests.

After the eggs have hatched, thistles provide their second benefit: Food. Goldfinches are mostly seed-eaters and they delay raising a family – with a bunch of hungry mouths to feed – until mid-summer when the season of seeds is well underway. Probably their favorite seed is the thistle.

“Cursed is the ground because of you,” God told Adam in the Garden of Eden. “Thorns and thistles it shall bring forth for you.” Clearly, a man’s curse can be a bird’s blessing.

Nest success

This is the time of year when birds are building and using nests. But as parents, birds are often unsuccessful, both at building nests and at protecting their occupants.

Bad weather and faulty construction can lead to nest failure. But most bird nests are also subject to predators. Various studies of nest predation have found that between a third and a half of nests are attacked by other birds, small mammals, and reptiles such as snakes.

Percentages of predation can vary widely. A study of Hermit Thrushes in Arizona found that predators attacked 83% of the nests. A study in the same state of Black-headed Grosbeaks found predators attacked only 23% of the nests.

Dr. Steven W. Kress reported a study that found that of 100 Song Sparrow eggs, 74 hatched successfully and 52 eventually fledged. That’s a loss of nearly 50%.

Years ago, Dr. Arthur Allen of Cornell University estimated that less than 20% of all nests succeed in producing a complete set of new, mature birds. But as Allan and Helen Cruickshank point out, that’s nature’s checks and balances. “Should all of the birds’ eggs laid in North America in a single season not only hatch but the young mature,” they said, “the continent itself would be so crowded with birds that man himself would suffer acutely.”