Most people would be puzzled by the new 30-foot brick tower that stands alone at the entrance to the Prairie Ridge Ecostation in West Raleigh, but the people who built it hope that thousands of birds will know exactly what it’s for.
The tower was designed to look like a chimney from an old school or office building, the kind that attract chimney swifts by the thousands during roosting season, from August to October.
Those chimneys are becoming rarer, so the N.C. Museum of Natural Sciences and the Wake Audubon Society teamed up to build a new one specifically for the birds.
“They’ll always have this chimney even if we lose every other place in Raleigh,” said John Connors, a Wake Audubon board member and retired coordinator of the museum’s Naturalist Center.
For most of their history, these birds roosted mostly in massive hollow trees such as cypress, hemlock, sweet gum and sycamore. Had the birds been given their name then, they would be known as “hollow tree swifts.”
But as those trees disappeared, the swifts adapted to chimneys that rose in their place. In the Triangle, the birds pair up and build nests in small chimneys from April through July.
Come August, though, the swifts revert to their true nature as social birds when they gather each evening in big flocks to roost in large chimneys. Using their feet and tail feathers for support, they cling to inner walls, packed in by the hundreds or thousands for the night.
The gathering of the birds in the evening is a spectacle, as they circle and circle and call out. It’s thought that this staging attracts other birds, a way of advertising the site of a good roosting spot. How many return to the same roost from night to night is one of the many mysteries surrounding chimney swifts.
The evening tornado of birds is also what makes chimney swifts so popular with birders and science educators trying to appeal to school students or the general public.
“It’s a phenomenon,” Connors said.
In the morning, the birds take off to look for insects, usually in small groups, said John Gerwin, the museum’s curator of ornithology.
“They’re very dispersed during the day,” Gerwin said. “Then they flock up for the roost.”
The roosting continues until early October, when the flying insects that make up their diet begin to die off and the swifts head toward their winter homes in South America.
Their departure also coincides with the firing up of the heating systems attached to the chimneys; swifts won’t use a chimney with smoke or hot air pouring out of it.
The heyday for chimney swifts was probably the 1950s, when every sizable building with central heating had a chimney. The birds are now declining at 2 percent to 3 percent a year, though scientists really don’t know what’s a normal population size for a bird that has adapted to its environment the way the chimney swift has, Gerwin said.
The problem for swifts is that modern heating systems don’t come with chimneys, and old ones disappear. Wake Audubon Society did a survey of Wake County schools in 1998 and found that more than 30 had chimneys used by swifts for roosting.
By last year, only 7 of those roosts remained, as schools either tore down their chimneys or capped them.
The Prairie Ridge tower is a little over six feet square, with 8-inch thick walls. It has port holes and small metal doors for cameras, cords and other equipment, so scientists can watch the birds and maybe eventually count them as they come and go each night.
It cost $36,000, even with donated bricks and the design donated by the firm of architect Frank Harmon. Designer Jacob Burke said it’s his first chimney swift tower and that “it would be cool if it wasn’t my last.”
Birders and scientists have built wooden towers for individual pairs of chimney swifts to nest, but this is one of the first designed to attract thousands of birds to roost.
By September, there will be a viewing patio with benches to make it easier to watch the birds. Connors said they hope that as many as 4,000 will roost in the Prairie Ridge chimney by then, though as with so much about chimney swifts, it’s not clear how the birds will find the relatively small openings in a landscape of trees or roofs.
“We don’t know if they’ll come,” Connors said. “They should come. They’d better come.”