Surveying the flocks of migrating birds at Presque Isle, an Erie Bird Observatory hike leader snapped, “They should call the blackpoll warbler the “fat poll warbler.”

“There’s nothing better than a fat bird in the fall or anytime,” another bird researcher added.

“If you are a bird, being fat means you’re healthy and that the environment is a quality habitat,” said Mary Birdsong, lead shorebird monitor for the observatory.

Blackpoll warblers are small black-and-white songbirds that turn yellow-green in the fall. It is 5 1/2 inches long and typically weighs between 10 and 12 grams.

They can double their weight for fall migration, said Annie Lindsay, bird banding program manager at the Powdermill Nature Reserve in Cook Township, Westmoreland County.

They need the extra fat. Vanity be damned.

“Once they hit the Atlantic coast, blackpolls don’t stop and arc over the Atlantic Ocean to South America,” Lindsay said. “That’s at least a 72-hour flight in good conditions.”

Blackpolls embark on the longest overwater journey of any songbird at nearly 1,800 miles, according to the Cornell Lab of Ornithology.

The birds breed in the boreal forest of Canada, migrating through Pennsylvania on their way to the East Coast in the fall, then to northern South America.

Powdermill, a research station for the Carnegie Museum of Natural History, is just starting to see them at the banding station this season, Lindsay said.

Fall land bird migration runs roughly from early August through November. Southwestern Pennsylvania is entering the fall peak of migration now.

Bird banding at Presque Isle will continue through the end of October on Fridays, Saturdays and Sundays from 10 a.m.-2 p.m., weather permitting. Look for the sign at Fry’s Landing for free public presentations.

Powdermill will host free open houses this Saturday and Oct. 21, from 8 a.m.-noon. The public is invited to visit on those days to see the bird banders work with migrating birds caught in mist nets.

Fat for fall

“Anything that migrates has to gain fat mass,” Lindsay said. “Migrating hummingbirds, Swainson’s thrushes and warblers — they’re pretty fat now, too.”

For migrating birds, the extra weight can be seen sometimes after they take off to fly. They may dip down a little before gaining momentum, she noted.

To gain weight, birds do what people do. They eat a lot.

Called hyperphagia, or excessive eating, the birds’ voracious appetite results in major changes in their body weight, Lindsay said.

Hummingbirds, which weigh only about 3 grams, add a few tenths of a gram or more before migration, she said.

Sarah Sargent, the executive director of the Erie Bird Observatory, banded a Swainson’s thrush last weekend and wowed a crowd with this line: “This bird is flying to the Andes Mountains in South America.”

The tan and white speckled bird, a diminutive relative of the robin, was caught in a mist nest and retrieved by volunteer bird banders. Sargent took the bird out of a cloth bag to measure its wings and weight. The bag was stained purple because the birds gobble up pokeberries in large stands on Presque Isle.

“When birds stop off here, they eat a lot of berries and they eat a lot of insects,” she said.

Sargent held the 7-inch bird in the palm of her hand, gently blowing on its stomach to see the skin under its feathers, looking for fat deposits.

‘Loaded’ birds

The average weight of a Swainson’s thrush is about 32 grams. “When they are loaded” in the fall, they can weigh about 40 grams, she said.

Typically, many land birds migrating in autumn gain one-quarter to one-third of their normal weight.

Since birds need a nutritious diet to pack on those extra ounces and grams, native trees and shrubs like dogwood and serviceberry work best to help fuel birds on the move, Lindsay said. That’s another reason for property owners to plant native trees and shrubs, she added.

On many nights during fall migration, over 10,000 migrating birds pass through Pennsylvania. Knowing that, the Carnegie Museum of Natural History’s BirdSafe Pittsburgh works with other local nonprofits to study birds that hit local buildings.

Bright lights can disorient migrating birds that fly at night, causing window collisions. BirdSafe asks residents and businesses in the region to dim or turn off unnecessary lights from midnight-6 a.m. from now until Nov. 15.

Forecasts for bird migration are available from Cornell Bird Lab’s BirdCast online, pinpointing concentrations of migrating birds by using radar, weather forecasts and other data.

Tailwinds welcome

Spoiler alert: Migrants like tailwinds for an easier trip. In the fall, the birds aren’t in a hurry as they are in the spring, Sargent said.

“There is a big race for birds in the spring to get to the best breeding grounds and establish territory,” she said.

In autumn, they are recovering from breeding and taking their time to head to their wintering grounds down south.

The numbers of migrants vary. On a big day, the banders at Presque Isle catch 100 birds. On a slow day, it’s more like 20.

“It’s normal for the flights to go in waves because of weather patterns,” as birds take advantage of tailwinds and cold fronts, Sargent said.