Marcia Bonta

American Robin

Eat and Be Merry 2, by Today is a good day (Creative Commons)

Note: Though most of the other posts on this site are reprints of my columns in the Pennsylvania Game News, I wrote this one for Birdwatcher’s Digest, where it was the cover story for the January-February 2008 issue.

American robins remind me of old-fashioned, dignified businessmen of an earlier era. I almost expect them to pull out watches from their vest coat pockets. They also have a whiff of the sanctimonious about them, “tut-tuting” at everyone else’s foibles, as they run erratically over our lawns and golf courses. Then, in early November, on our central Pennsylvania mountaintop, the Hercules’ club berries, which hang in tempting purple clusters, ferment. Suddenly, our sober robins become drunkards. They sing as they gorge themselves and unlike their fellow drunks, the cedar waxwings, who manage to retain their staid, unruffled demeanor, the robins look more like bumbling, overgrown school boys on their first bar crawl. Fluttering like butterflies as they try to balance themselves on the tops of the bowed, berry heads, they also scratch in the leaf duff and poke in the ground, searching for earthworms and other insect food, loathe, perhaps, to imbibe on an empty stomach.

In the fall, robins are intoxicated by a variety of fermented fruit and, as L.A. Eiserer describes them in The American Robin: A Backyard Institution, robins “show all the signs of inebriation. They flap, flop, flutter, and stagger. Sometimes they even pass out…” When drunk they may fly in front of a car or into a window.

To see robins change from reliable, upright birds to tipsy, irrational alcoholics makes me mindful of their seemingly split personalities. In spring and summer, they boldly inhabit our yards and gardens and often raise their young in nests close to and even on our homes and garages. But in fall and winter, they retreat south into woods and swamps and shy away from humans.

Such changes, though, are understandable if you know the life history of these common but fascinating songbirds. For instance, male American robins fly to a roost every evening of the year. Females join them except during the breeding season. And as soon as their first batch of fledglings can fly well, the males escort their young to the roost. So inbred are their ties to roosting that even hand-reared fledglings, at 13 or 14 days of age, develop a restlessness toward dusk at the same time that wild robins are heading for their roosts. These roosting aggregations are not always composed solely of robins–kingbirds, brown thrashers, cedar waxwings, red-winged blackbirds, swallows, brown-headed cowbirds, common grackles, American crows or orioles may join them.

Unlike the fairly stable roost site during breeding season, those during migration and in the winter fluctuate. But the ideal roost site contains dense vegetation, saplings, and thick, berry-covered shrubs near a stream and field in either secluded woods and/or inaccessible swamps. Enormous numbers of robins have been recorded at some winter roosts — one million robins in Virginia’s Dismal Swamp, 50,000 in a Florida cypress swamp, 165,000 at Lakeside Park in Oakland, California, and 3,500,000 near Fertile, Missouri.

“At sunset the sky is black with Robins coming in to roost, and at daybreak when they are leaving the sound is like a train passing over a trestle,” one observer at an Alabama roost wrote back in 1931. Robins are not faithful to the same wintering grounds. They go where the food is and prefer temperatures between 40 and 60 degrees Fahrenheit. Most winter in the southern United States, but if the food supply is good and the winter, relatively warm, significant numbers of local robins may not migrate. Even on our cold mountaintop in January and February, many robins remain if the wild grape crop is plentiful.

One cold, February morning, I found the mother lode of robins–hundreds of them, some singing, as they gorged on wild grapes. During another grape-filled winter, I sat beneath wild grape-draped trees and watched as robins, accompanied by cedar waxwings, European starlings, and a couple northern flickers, harvested grapes on the vines and frozen ground. I dared not move as wild grapes plopped down around me. Sitting there in the warming sun, encircled by the birds of spring in a winter woods, the ground patched in white, I felt as if I was part of a winter mirage. But wherever I walked that February morning, more foraging robins swept over the landscape. During such fruit-filled winters, I don’t know when to record the first returning spring robin.

But then are robins truly harbingers of spring? Partly yes and partly no. Most do migrate south in the winter and, beginning in late February, fly north in fits and starts, depending on the temperature, which must be at least 37 degrees Fahrenheit, and the weather. If it suddenly turns cold or begins snowing or sleeting, they may head south again until the weather moderates.

Many robins follow the Mississippi River Valley north with western robins taking the Missouri River fork and eastern robins the Ohio River. Others prefer forested routes. The closer they come to their breeding grounds, the faster they travel, although robins on the Pacific coast migrate faster than those in the rest of the country.

Most return to or within ten miles of their birthplace, the males several days ahead of the females, looking fat and fit and arriving in a flock. Those robins that have not migrated are often alone or in pairs and are scrawny. So a single robin does not a spring make but a flock does. When our First Field fills up with robins one bright, warm day in mid-March, I know that spring is on its way.

And where else do these birds return to? These largest and most widespread of North American thrushes breed throughout most of North American from Alaska in the west to Quebec and Newfoundland in the east and south to Florida and Mexico. Robins have been extending their range since the beginning of the twentieth century, moving west into the Great Plains and south and west into Florida, Texas, Arizona, New Mexico and California, as we have moved into those areas with our well-watered lawns and pastures, which have introduced or brought to the surface earthworms, and have planted trees in prairies and deserts.

Robin, watercolor, c. 1895, by Louis Aggasiz Fuertes (public domain)

Open, grassy areas near trees and shrubs provide ideal breeding and feeding habitat for these most versatile of songbirds. In addition to earthworms, robins eat a wide variety of wild and cultivated fruits and both terrestrial and foliage-dwelling insects throughout their range, consuming primarily fruit in the fall and winter and insects and earthworms in the spring and summer.Once the males return, they reclaim their old territories, and when the females join them several days later, they too are more interested in returning to their former nesting area than in either courtship or loyalty to previous mates. A female robin will even help defend her mate’s territory or defend it if her mate dies. Often the territory encompasses only that area around a nest and territories sometimes overlap. Other robins will even help each other defend their nests from predators. Seemingly, excellent territory–wide stretches of short-cropped grasses–is frequently unclaimed and serves as a communal feeding ground.

To keep his territory and attract a mate, the male sings his familiar “cheerily” song. Robins begin singing very early in the morning and are one of the latest singers in the evening. They sing most during courtship and until the young hatch. Then they are silent until the young fledge when they resume singing. July and August, when robins molt, are silent times, but in late September, they sing during what one researcher calls their secondary song period. They also have a “whisper” or “hisselly-hisselly” song, described as similar to ethereal hermit thrush vocalizations. Donald Kroodsma, in his definitive The Singing Life of Birds, has studied robin song extensively and writes that “…each male robin has a largely unique repertoire of caroled phrases that I can use to identify him as an individual.”

Alarm calls are the familiar “chirp,” “yeep,” “cuck,” or “tut,” which are made when robins spot predators such as northern harriers, sharp-shinned, Cooper’s, red-tailed and red-shouldered hawks, American kestrels, merlins, and peregrine falcons, or to communicate with their young during nesting time.

Once a male attracts a mate, the relationship is monogamous during the season. According to John James Audubon, the male robin displays for the female by spreading and lifting his tail, shaking his wings, and inflating his throat. The male and female robins also approach each other with wide open bills in what researchers refer to as “ceremonial gaping.” Copulation usually occurs after day singing and is “brusque, businesslike, and to the point,” writes Eiserer.

The female selects the site and builds the nest, and he helps by bringing in nesting materials. The first nest in early spring is usually built in a low evergreen such as the 10-foot-tall juniper tree outside my bedroom window, but later nests are often constructed higher in a deciduous tree, where the thick leaves provide shelter from rain. Robins, though, are known for improvising where nest sites are concerned, and north of the tree limit they will build on cliffs. Even where there are plenty of trees and shrubs, they often nest on human-made structures such as fencepost tops, porch railings, outhouses, telephone booths, and roof gutters. Years ago, we took a six-week vacation in spring and returned to find a robin’s nest, crammed full of nestlings, on top of a garden hoe hanging in our garage. Needless to say, we waited until the robins fledged to hoe the weeds in our vegetable garden.The outer wall of the nest is made of dead grass and twigs, to which the female may add feathers, moss, white paper, cloth, wool, or mammal hair. Then she uses mud from worm castings to cement nesting materials in place. Finally, the female lines her nest with fine pieces of dried grass.

Unlike most songbirds, which lay their eggs at sunrise, she lays her 3 to 4 sky-blue eggs in late morning or early afternoon. She incubates her eggs from 12 to 14 days, and the eggs hatch in the order they were laid over a 2- to 3-day period.

Both parents feed the nestlings. For four days they are fed regurgitated soft parts of insects, earthworms, and plant material. After that, broken and then whole earthworms, as well as caterpillars, ants, flies, beetles, adult moths and butterflies, centipedes and millipedes are stuffed down their open beaks by their parents who work from dawn to dusk. Researchers estimate that each brood of robins eats 3.2 pounds of food and that on their last day in the nest each nestling may eat 14 feet of earthworms. They are fully feathered at 8 days of age, and by the time they fledge, at 13 days old, they have grown 1,000 percent–from 5.5 grams at hatching to 56 grams. Usually they leave the nest one at a time over a 24-hour period, but if something disturbs them, they leave, Eiserer writes, in a “flapping explosion of plump and chirping cannonballs that scatter in all directions.”

In addition to incubating eggs and feeding nestlings, robins must defend eggs and nestlings from a wide variety of predators — Steller’s, blue, western scrub, and gray jays, American crows, common ravens, common and great-tailed grackles, raccoons, bobcats, black bears, chipmunks, fox, gray and flying squirrels, and black snakes. Night predators on nestlings, fledglings and adults include eastern and western screech-owls, great horned, snowy, long-eared, barred, and northern saw-whet owls and northern pygmy-owls. But all the wild predators together do not kill nearly as many robins and their young as house cats do.

Yet these birds, which are “as American as apple pie, baseball, and the Stars and Stripes,” writes Roland Wauer in The American Robin, continue to thrive and even increase over much of their range, because unlike most of our songbirds, deforestation, urbanization, and increased agriculture have been a boon, not a bane, to them. American robins are indeed America’s backyard bird.

January 17, 2008 Posted by Marcia Bonta | American robin, Animal Behavior, Birds | 6 Comments