In Vermont, it’s not the robin that tells us spring is on its way, but the blackbird. The red-winged blackbird is one of the first songbirds to fly back to the snowy north as spring approaches. Birders began to report these marsh-dwelling birds in early March, with more arriving each week.
Although the intense cold of early March undoubtedly slowed the spring arrivals, Vermont eBird, a website through which birders can submit their observations, tallied 238 red-winged blackbirds sighted in the first half of March and 922 in the second half.
American robins, those portly, red-bellied birds who supposedly forecast spring, actually spend the winter in Vermont, so sighting one in March is no big deal.
Although blackbirds are among our first returning migrants, black-capped chickadees actually scoop the blackbirds by starting off the spring chorus. Year-round, chickadees buzz their “chickadee-dee-dee” call, but it’s in February that these dapper gray, black, and white birds begin to sing their simple, two-note song, signaling that spring is on the way.
“It’s about to pop,” said Rosalind Renfrew, conservation biologist with the Vermont Center for Ecostudies. All that’s needed is slightly warmer weather. When it does pop, we’ll see loons and other waterfowl return to the lakes; song sparrows to any open, shrubby area; and killdeer to agricultural fields.
Other birds that return north in late February to early April include turkey vultures and tree swallows. Turkey vultures spend the winter just south of here, where snow is less likely to cover up food sources. Tree swallows, who feed on swarms of insects by swooping through the air with their mouths open, fly north from sunny Florida, the Caribbean and Mexico.
One harbinger of spring, the woodcock, will appear when the snow melts enough to reveal bare patches in fields. American woodcocks pull grubs out of the ground, so they need access to unfrozen ground in order to eat. More notable to the human observer, however, is the woodcock’s mating display.
“They’re one of the quintessential spring phenomena in the bird world,” said Renfrew. “They start by making this sound sitting on the ground and they fly up and they make all sorts of different twittering sounds and making spirals way high up in the air and they spiral down to the ground again and sit near where they started and make that sound again.” To make the twittering sounds, woodcock pass air through their outer wing feathers.
Another obvious sign of spring is made by woodpeckers: drumming.
“That’s a not-so-welcome sign of spring sometimes,” said Renfrew.
Although most of Vermont’s woodpeckers overwinter here, one species will soon arrive from out of state. The yellow-bellied sapsucker has a drumming pattern that starts fast then slows down. “They’re the ones that are famous for pounding on the loudest thing they can find, like your house or mailbox,” explained Renfrew.
What is it that leads these birds to change their behavior when there is still snow on the ground and sub-freezing temperatures?
According to Renfrew, the primary factor is the increasing amount of daylight. This triggers the production of a group of hormones in birds called gonadotropins. These hormones lead birds to change their behavior in several ways.
First, the birds that migrate get what ornithologists call migratory restlessness. They begin to pack on fat stores for the long haul back to their breeding grounds. Then they take off. When they arrive at their destination, they begin to sing.
Although birdsong sounds harmless to human ears, it means something else to birds: it tells other birds to stay out of the singer’s territory. In most songbird species only the males sing, as they are the ones that establish territories. Females often select mates based on the size and quality of their territory, because territory size and quality affects the survival of young. According to Renfrew, as spring approaches, the part of the bird brain that deals with vocalizations actually increases in volume — meaning that birds are more focused on establishing and maintaining territories.
It’s been a long, cold winter, not just for humans. Although in the Northern Hemisphere many birds respond to the lengthening days by migrating north, that response is tempered by the weather. The exhausting experience of flying long distances means a bird needs to eat heartily upon arrival. If the food is covered by snow, or otherwise unavailable due to the cold, arriving migrants may die of starvation.
“Usually red-winged blackbirds are showing up and starting to sing around the end of February, the first week of March at the latest. The first report of one this year was on the ninth of March,” said Renfrew.
Because getting hold of a good territory is usually essential for a successful mating season, it behooves males to arrive at the breeding grounds as early as possible. If they arrive too early, however, a late-winter storm could kill them or their food supply — so “they’re always trying to find that sweet spot,” said Renfrew.
That sweet spot is fast approaching, to the delight of birds, birders, and those who simply need reassurance that, after the long winter, spring is finally here.