On the wild side—March, 2012
by Tina Mitchell
Can you imagine a spring without American Robins, singing their bright, lilting “cheerily, cheer up, cheerily, cheer up” song? Michigan State University (my alma mater—go Spartans!) faced this catastrophe in 1959. In the early 1950s, arbor specialists began trying to eradicate Dutch elm disease on campus by spraying the many elm trees with DDT. The insecticide manufacturer had assured them that the spray was not harmful to birds. But the oily residue stayed on the leaves; the leaves fell to the ground; the earthworms ate the leaves; the robins ate the earthworms. Within a week after each new wave of migrants arrived in the spring, all of the robins were dead. By 1959, robins had been completely extirpated on the vast, bucolic campus. Faculty ornithologists eventually identified the culprit—as few as 11 earthworms delivered a lethal dose of poison to a robin—and stopped the use of DDT locally. This investigation was one of the cornerstones of Rachel Carson’s powerful and ground-breaking Silent Spring, which resulted in the banning of DDT as a pesticide throughout the U.S. And happily, the MSU robin population had returned to its pre-1950s level within 2 decades.
The American Robin is the largest species in the thrush family, which includes not only all bluebird species but also some of the most talented songsters in the avian world. (Among my favorites are the Townsend’s Solitaire, Wood Thrush, Hermit Thrush, Veery, and Swainson’s Thrush.) American Robins inhabit every state in the continental U.S. and much of Canada. The only areas of Colorado that don’t host breeding robins are those without trees—croplands, grazing lands, or agricultural fields, for instance. Saddled with the easily ridiculed scientific name of Turdus migratorius, its name derives from the Latin term for “wandering” (migratorius) and “thrush” (turdus). (Since most thrushes wander (migrate), it’s not really clear why the robin was singled out for this particular moniker.) Its common name arose from homesick European settlers in the U.S., who thought the birds looked like the English Robin (currently called the European Robin—see photo, above right), commonly found in Europe (but to which our robins are not closely related).
In Colorado, we likely have two groups of American Robins—those that breed here in the summer and those that winter here. In our specific area, we find robins in the pinyon/juniper habitat only in winter, eating lots of juniper berries. To raise their young, though, these birds (or another group of birds—no way to know for sure) move to the deciduous habitats such as by the Arkansas River, where soft-bodied invertebrates such as earthworms abound.
Adult males and females look quite a lot alike, although you can often differentiate them by the color of their heads: Males’ heads are much darker—almost black—than their gray-brown backs while females’ heads are more gray and show less contrast to their backs. (The photo in the first paragraph is likely a male; the photo to the left here, a female.)The female robin chooses the nest site, typically on horizontal branches of a tree but also in gutters, on outdoor light fixtures, or other human-made constructions. They seem to tolerate nesting close to human activity. (We had a pair nest on a 6”x6” wooden brace under our patio roof in Lakewood—just outside our kitchen window, providing lots of fun watching the 3 nestlings grow up.) Both parents take an active role in feeding nestlings. For the first few days after hatching, parents regurgitate soft invertebrates (e.g., grubs), parts of worms, and even some plant material (e.g., fruit) for the babies. After that, the parents just directly fill the gaping mouths with a variety of invertebrates and, occasionally, small fruit. Nestlings fledge about 13 days after hatching—often when they can hardly fly at all—and are fed by their parents for at least another 3 weeks. Juveniles are easy to identify—they have black spots on their breasts and pale spotting on their backs. The male will often take primary responsibility for feeding the first brood of fledglings while the female starts a 2nd brood.
A robin’s fall and winter diet is 90% fruit; but in spring and summer, it flips to 90% invertebrates—especially earthworms. When a robin is hunting earthworms, it looks like it is listening for them, cocking its head to one side and then to the other before pouncing. But the noise that earthworms make is too faint to be heard above ambient sound. Robins are actually using visual cues to detect the worms under the soil. Studies of captive robins indicate that they seem to prefer blue and red fruits (e.g., blueberries, strawberries) over yellow or green fruits. When robins eat a large number of honeysuckle berries, they have been documented as actually becoming a bit intoxicated! As is true for many thrush species, robins love bathing in water. Watch a robin splashing exuberantly in a birdbath and you’ll likely feel a strong desire to join in the fun.
Those of us in dry pinyon/juniper habitats will soon be bidding the local winter American Robins adieu for a while—instead, hearing their lovely songs from afar around creeks and the river. During breeding season, robins are the last to sing in the evening twilight after sunset. And they greet the morning long before most humans and other birds are up—as much as an hour before dawn. This characteristic indeed gave rise to the adage “The early bird catches the worm.”
You can see more photos and learn more about American Robins here.