Many birds from our region fly south for the winter. But there’s an arctic bird that flies to New England for the winter thats not the snowy owl. This arctic bird that overwinters in our region is the snow bunting (Plectrophenax nivalis).
How do these little songbirds withstand our frigid winter temperatures, the ones that force other birds to flee? For one, snow buntings have exceptionally dense feathers that cover their legs and the base of their beaks. These feathers trap heat and minimize exposure to the cold and wind. A snow bunting’s body temperature can get 30 to 40 percent lower than the body temperature of other songbirds. During snowstorms and blizzards, snow buntings burrow into soft snowbanks to escape the wind and retain heat.
These birds have been recorded farther north than any other songbird in the world. Many types of birds stay on one continental mass, but snow buntings circumnavigate the northern hemisphere; flying south could bring it to North America, Europe, or Asia. They spend their summers in arctic places like Greenland, Alaska, Canada, Scandinavia, and Siberia. In winter, they fly south to warmer locations like southern Canada, the northern United States, northern Europe, and central Asia.
Because we are at the southern edge of the snow buntings’ range, the flocks we see in winter are mostly female. Males overwinter in colder, more northern regions, where they can get back to their breeding grounds more quickly. In Winnipeg, 700 miles north of here and one of the coldest cities in North America, the flocks in winter are mostly male.
Dusted in cinnamon
Snow buntings look different in winter and summer. Many birds molt twice a year, in the spring and the fall. Snow buntings molt once, in late summer before they fly south. At this stage, their feather tips are brown and their heads look like they are dusted in cinnamon. Over the winter, the males rub their heads and bellies on the snow, wearing away the brown tips of their feathers. By the time they return north, males are mostly white with black markings. Females become whiter, too, but not as white as the males.
Before their spring migration, snow buntings eat a great deal to build up fat reserves. Their fat mass increases by 30 percent. Their chest muscles thicken to help them stay warm and to make the long flight north. For females, fat reserves provide energy for egg production.
To stake out the best nesting spots in rock crevices, the males return north first, using magnetic cues to migrate at night. They often return north in early April when the temperature can still drop to –20°F. (They can withstand temperatures as cold as –50°F.) Their white plumage helps them blend in with the snow. Females arrive about a month later, when temperatures are slightly warmer and the snow starts to melt.
As soon as male snow buntings reach their northern breeding grounds, they begin doing what songbirds do — they sing. They sing almost nonstop until they find a mate, pausing only long enough to find food. Therefore, males who are successful foragers spend more time singing. Females select mates who sing the most, as this indicates their ability to find food. And a female needs a mate who is good at finding food.
Why? Because the air temperature is so low, a nesting female cannot leave her warm clutch of eggs to find food. Instead, she relies on the male to feed her. And he does. The male brings the female food every 15 minutes or so. (These birds need to eat frequently because they burn so many calories in the cold temperatures.) Later, when the chicks hatch, the male brings insects to the chicks. One study showed that widowed female snow buntings raised half as many fledglings as those who had a male partner.
In our area you might see snow buntings along shorelines, in fields and grasslands. They are ground foragers, collecting seeds from the ground and lower plant stems. People have seen them along the river near Assembly Square in Somerville, and along shorelines in Boston and environs. They can be difficult to spot because they blend in with the environs, but they are also restless in the winter, flying to a new foraging spot every few minutes. So keep your eyes peeled for undulating flock movement, as these songbirds dart around en masse.
As the planet warms, what does the future look like for snow buntings? Studies indicate that warmer springs cause snow buntings to return north earlier. When they breed and nest earlier, there are fewer insects available when the chicks hatch, leading to fewer surviving offspring. In addition, warmer temperatures mean that other species might move north to compete with snow buntings. The conservation group Partners in Flight reported in 2016 that the snow bunting population has declined 38 percent since 1970.
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