Saturday, June 22, 2024

Male rose-breasted grosbeaks, or cutthroats, sport a blood-red patch on the neck. (Photo: Margaret Lewis)

The male rose-breasted grosbeak (Pheucticus ludovicianus) is striking and difficult to miss. He sports an upside-down blood-red triangle across the neck that looks as if he has suffered a stab wound. Hence, its nickname “cutthroat.”

Closely related to the cardinal, the grosbeak has a similar style of stout beak. In fact, the word grosbeak is from the French, meaning “large beak,” and this one is useful for splitting open the seeds that are an important part of the grosbeak’s food intake. Still, small critters such as insects, spiders and snails – picked off tree leaves or snatched in midair – make up at least half of its diet. They also eat fruits and berries in season, and milkweed, sunflower and catalpa seeds.

A female rose-breasted grosbeak at Horn Pond in Woburn on May 4. (Photo: Margaret Lewis)

Rose-breasted grosbeaks are common in the woods of New England, but in the winter they migrate thousands of miles south to tropical regions of Central and South America, where food is plentiful. In the spring, they make the long trek back north. Most grosbeaks fly across the Gulf of Mexico in one night, a distance of about 500 miles. On average it takes 15 hours of nonstop flying for these 8-inch birds to complete the journey. Wind and rain can slow them down, however, so the trip can sometimes take longer. When they reach the end of their journey, they are understandably ravenous and depleted. A few birds take the longer land route around the Gulf rather than over it.

This female grosbeak in Cambridge, like all females, is a streaky brown color with white stripes. (Photo: Becca Evans)

Some rose-breasted grosbeaks overwinter in South America and Panama; these birds return in the spring to New England and eastern Canada. Others overwinter in Mexico; these return to the western states. Once grosbeaks reach their northern breeding ground, they feed and reproduce. Then they molt and fatten up until it is time to fly south again. During this late summer molt, the males lose some of their red, black and white feathers and become more brownish.

A male collects foliage for a nest in Sherborn on May 9, 2021. (Photo: Richard George)

You certainly have heard the question, “Which came first, the chicken or the egg?” Another question puzzling scientists has been, “Which came first, migration from the north or migration from the south? Did birds first start flying south to the tropics to overwinter where food is abundant, or did birds first fly north for better breeding conditions?”

To answer this question, scientists looked at the evolution of 800 species of songbirds. They modeled the distribution of these birds throughout time. This helped them estimate how each bird’s migration patterns have changed. They determined that migration evolved from birds shifting their wintering ranges farther and farther southward. In addition, scientists discovered that many nonmigrating tropical birds evolved from migrating birds who stopped migrating.

A female gathers material for a nest in New York on May 20, 2022. (Photo: Tom Murray)

Because of climate change, many bird species that migrate short distances return north a week or two earlier than they used to. But long-distance migrants have no way of knowing what weather conditions are like thousands of miles away. The timing of their migration is encoded in their genes. They do not migrate north early even if conditions in the north warrant it. They migrate at the same time each year. This means that these birds may no longer be migrating when they will most benefit from spring leaf outs and the emergence of larvae, which most songbirds feed to their young.

Males have red underwings, while on females they’re yellow. (Photo: Richard George)

Can these late arrivals play catchup by shortening the time it takes for them to form pair bonds, build a nest and lay eggs? Some long-distance migrants seem to be doing it. But will this adaptation be enough as our climate continues to warm in the future? Only time will tell.

Red-breasted grosbeaks form pairs in the spring after they arrive in their northern breeding grounds. The females approach a singing male, who has established a territory. If interested, the male begins a courtship display, which includes a warbling song and fluffing out his tail and wings. Once paired, the male and female work together to build a cup-shaped nest using forked twigs, weeds and leaves. They work from first light to darkness for about a week. The nests are often so thin that a person can see the outline of the eggs in the nest when looking from below. The completed nest is about 6 inches in diameter and 3 inches deep. In the nest, the female lays about four spotted greenish-blue eggs, which hatch in about two weeks.

Males are black and white when seen from above. (Photo: Tom Murray)

Both parents feed the nestlings. According to the observations of Arthur Cleveland Bent in 1877, 

Occasionally both birds were busy caring for the young at the same time, but generally they took turns at half-hour intervals … During one of the male’s turns at feeding he came and went twenty-eight times in thirty minutes, always bringing elderberries from a bush only a few feet distant and feeding the same nestling fifteen times in rapid succession.

To study up on the rose-breasted grosbeak or other birds today, you are likely to search online for information. According to biographer William Sloane Kennedy in 1899, the best way to go birding in Cambridge is as follows:

Make a preliminary visit or two to such a museum as the Agassiz, in Cambridge, Mass., and look carefully at the cases holding the American birds, taking notes and fixing in your mind the general features of the different species. The next thing to do, of course, is to get where the birds are and observe them … Our rose-breasted grosbeaks are usually difficult to observe close at hand, but this morning (May 19) a male grosbeak alighted on a telegraph wire, ten feet above my head, on a main-traveled road, and showed no signs of fear whatever … From four to eight o’clock in the morning is a great time to see and hear birds, and one will rue it who goes out from 9 a.m. to 4 p.m., expecting bird victories … If you have the four-o’clock-in-the-morning courage, however, you can know all the birds, and still earn daily wages throughout the year.

I don’t know many people who have the 4 o’clock courage, but luckily for us, rose-breasted grosbeaks are not the earliest of birds. You might be able to observe them at feeders around 6:30 to 7 a.m. They spend much of their days in treetops, so a good pair of binoculars can help.

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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.