Each fall, not only do birds fly south from Pennsylvania, and fly south through Pennsylvania, but some birds actually fly south to Pennsylvania, according to Franklin Klock, a naturalist at the Carbon County Environmental Education Center.
In the midst of January, birds of many a feather fill the trees outside the CCEEC, each waiting its turn to swoop down to one of the center's bird feeders.
On one winter day Klock noted that the trees were so populated with red Cardinals, and blue and white Bluejays that it looked as though the forest had been overlaid in a patriotic theme.
"We see Dark-eyed Juncos from up north upwards into Canada and Nova Scotia," Klock said. "Some of the birds that migrate into our area and overwinter here, are from past the Arctic circle.
"Rough-legged Hawks are a perfect example. We have two here at the center," he continued. "In the summer, they live above the Arctic Circle, but in the winter, they come here. We don't think of Pennsylvania as being south, but for them, it is."
Klock explained that it is a common misconception that birds migrate to get away from cold temperatures.
"Birds don't migrate because of temperature," he said. "They migrate because of food."
He said that by the time fall approaches most Pennsylvania song birds had eaten the best berries and seeds and aren't equipped to scavenge once the snow begins to fall.
But some birds are less finicky about what they eat and more resourceful at finding it in the winter. For example, the birds of summer tend to avoid the berries of the Arrowwood and the Firebush, while birds migrating from the north find them perfectly acceptable.
Birds used to the northern climates might have beaks and other adaptations that are suitable for pecking through a foot of snow, such as is typical in Pennsylvania, rather than three feet of snow as is typical in the northern reaches.
"Compared to up north, we get less snow," Klock said. "A foot of snow on the ground here doesn't stop a Bluejay from scraping to find acorns that dropped in the fall. It's not that there's food here and there isn't up there. It is just easier to get the food here."
At the bird feeders are Dark-eyed Juncos, Tufted Titmice, Cardinals and Bluejays. Pennsylvania is part of the year-round range of these birds, only there are far more of them in the winter.
Rather than the entire population of a bird species migrating, Klock explained that sometimes only part of a population migrates. He cites the Red-tailed Hawk as an example.
"Red-tailed Hawks are like that. It is not uncommon to see a Red-tailed Hawk in Pennsylvania in the winter, but it is uncommon to find an immature Red-tailed Hawk in the wintertime.
During their first and second year, they seem to be programmed to migrate south, but as they get older, they realize that there are mice, squirrels, chipmunks, rabbits here in the wintertime.
"It seems that as birds get older, with age comes wisdom," he said. "They discover how to find food here. This includes home bird feeders."
New migration patterns may have resulted from the human effect on bird habitat–farms replacing forests, housing developments replacing farms, homes with bird feeders.
Today, there is a wealth of man-produced food sources which make it unnecessary for a bird to migrate.
"Birds learn that if they get fed, they stay," Klock said. "Birds live near their food."
To avoid the snow, mice often scurry up trees to take over abandoned nests, and in the case of the center, bird boxes.
"They hop from branch to branch and will eat last year's new growth on trees and bushes," Klock said.
The overwintering birds stay until its springtime up north. With new plants growing, and insects hatching they return north where they do not have to compete with the returning snowbirds for food.