Sunday, July 14, 2024

A robin pulls a worm in Assembly Square, Somerville, in November. (Cody Matheson)

If you have ever heard a bird singing outside your window at 4 a.m., that bird was most likely a robin. Birds begin singing each morning at different times, but there is a specific sequence. American robins (Turdus migratorius) are the earliest singers in this dawn chorus. Blackbirds and cardinals are predawn singers, too, followed by pigeons, wrens and warblers. Finally, once it is daylight, the sparrows and finches chime in. Robins and other birds can sing for long stretches without stopping because they can sing while breathing in or out. Humans produce sound only when breathing out. (Try it!)

Male robins sing in the predawn hours to defend their territory and impress females. Research has shown that the noisier a location is, the earlier robins start singing. All this singing uses a great deal of energy on an empty stomach, especially after a cold night. Therefore, it is the strongest and hardiest males who sing the loudest and longest. These males are demonstrating to females that they are fit and healthy and can dominate a territory with good food resources.

A speckled juvenile robin in Magoun Square, Somerville, in February 2024. (Photo: Kate Estrop)

The arrival of daylight signals that it is time to stop singing and go about the activities of daily living. The rest of the morning and afternoon are relatively quiet. There are fewer songs as robins look for food, patrol their territory and court other birds. Robins are known for catching worms, and in the spring and summer they do eat many worms as well as beetles, grubs, caterpillars and grasshoppers. In fall and winter they eat mostly fruits and berries. Unlike hummingbirds, which will ingest great quantities of sugar water, American robins cannot digest sucrose, or table sugar. For this reason, they avoid sucrose-laden fruits and prefer fruits and berries that contain mostly glucose and fructose, such as cherries and grapes.

Early European settlers named the American robin after an English bird with an orange breast. These two robins are not closely related, though. The American robin is in the thrush family, along with bluebirds and blackbirds. The smaller European robin is a member of the flycatcher family.

For the first four days, robin parents regurgitate food into a baby bird’s open mouth. By day five, robin chicks eat small pieces of worms. (Photo: Tom Murray)

We think of robins as being migratory, but some male robins may stay around all winter. This makes it easier for them to stake out the best territories in the spring. If a winter is harsh, these overwintering robins may not survive and, under these circumstances, the first migratory spring arrivals will lay claim to the best territories. Overwintering male robins form large flocks that search together for winter berries. At night, these flocks roost together in trees.

To avoid predators, robins, who weigh less than 3 ounces (about the weight of three AA batteries), prefer to forage in short grasses. For this reason, humans with their expansive lawns, golf courses, pastures and sports fields have aided robin populations. Foraging robins typically take a couple of hops in the grass and then stop, cocking the head to point an eye and ear toward the ground – they can actually hear insects in the soil in addition to seeing them.

A winter robin finds food in Cambridge’s Huron Village on Feb. 20, 2022. (Photo: Richard George)

American robins really are early birds. Besides being the earliest bird to start singing in the morning, they are one of the first to lay eggs in the spring. Scientists have learned that robins will nest only when the noontime temperature is between 45 and 65 degrees Fahrenheit. But even more important than temperature is the relative humidity: It needs to be around 50 percent at noontime for robins to build a nest. Under these conditions, worms, grubs and insects move up near the surface of the soil. The robins need a steady supply of these invertebrates to feed their young. If conditions are not right, robins will hold off building a nest.

Females lay three to five blue eggs in a nest, often in a tree fork. The female keeps the eggs warm for two weeks until they hatch. Both parents feed the chicks earthworms, soft insects and berries. Since each chick eats its weight in food per day, the parents are feverishly busy during this period.

A robin finds a berry in Groton in January 2022. (Photo: Tom Murray)

According to ornithologist Edward Howe Forbush: “Both parents are extremely devoted to their young. During a sudden severe downpour of rain a mother robin sheltering her well-grown young on the nest was heard to give a piercing cry as she was unable alone to protect them fully from the flood. Her cry brought her mate; the two perched on opposite sides of the nest, breasts pressed together . . . bodies and wings sheltering the young like a pitched roof, while the rain ran harmlessly off on both sides.”

Robin chicks begin to fly two short weeks after hatching. According to the ornithologist Arthur Cleveland Bent: “The male parent takes practically full charge of the fledglings, enabling his mate to prepare at once for another brood. In a nest I had under observation, four fertilized eggs were laid in a nest six days after the young of the first brood had left it.” Frequently the male robin will escort the young robins to a roosting site far from the first brood. Despite all this parental care, only about 25 percent of young robins survive their first year.

By the fall, berries make up a large portion of a robin’s diet. This one was seen in November. (Photo: Tom Murray)

We associate robins with earthworms, but earthworms are not native to North America and have not always been here. Robins managed to survive just fine without them. In 1949, Bent published a note from a man in Canada: 

During the last half century the robin has increased in Alberta at least 100 percent. . . . When the hard prairie lands were broken up, … earthworms were absent, but with the arrival of the settlers, it was not long before the worms began to appear, especially in the gardens surrounding the buildings. The birds increased in numbers at about the same rate as the growth of garden space. It is believed that the settlers inadvertently introduced the worms with the potted plants and shrubs which they brought with them.

If you hear a relentlessly singing bird outside your window in the predawn hours, it is probably a robin getting a jump on the morning before all the human racket begins. Keep listening. Soon other birds may join the chorus.

A robin finds a trove of berries in November 2022. (Photo: Tom Murray)

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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.