To avoid having chimney swifts invade your home this spring, get your chimney capped — as soon as possible.
Swifts usually return in mid-April, but precise arrival dates are tied to weather, particularly temperature, which determines the activity of flying insects.
Swifts eat flying insects exclusively. You can check their northward progress at www.chimneyswifts.org.
Chimney swifts are those familiar summer residents that spend all day sweeping the sky for flying insects while twittering incessantly. At a glance, they resemble flying cigars.
At dusk, swifts assemble and descend en masse into chimneys where they roost for the night.
Hundreds or even thousands may roost in abandoned industrial chimneys. Residential chimneys may host a dozen or more.
Swifts are common in towns and cities where chimneys are seldom in short supply. They winter in the upper Amazon basin of Peru, Ecuador, Chile and Brazil.
Traditionally, chimney swifts nested in tall hollow trees, but as old growth forests disappeared, swifts adapted to other tall, dark, hollow structures such as chimneys, silos and abandoned wells.
Swifts are flying machines. Their long narrow wings, enable rapid, agile flight. They descend into chimneys headfirst, then flip tail-first once inside.
There they perch by clinging to the vertical wall. All four toes on each foot are directed forward so they can cling tightly to rough, vertical surfaces.
Their tail feathers are tipped with stiff spines that stabilize them while roosting. But because they lack a hind toe, they cannot perch or walk as most birds do.
Nesting begins in early May. Both parents use their strong feet to collect nesting material in flight. They swoop by small dead twigs, grasp them, snap them off and carry them back to the nest site in their bills.
Inside the chimney a layer of sticky saliva is applied to the twig. Then the twig is cemented to the chimney wall and to other twigs.
Eventually a nesting platform with a shallow cup forms. A typical swift nest measures about 3 by 4 inches, can take 18 to 30 days to build and may be placed as much as 30 feet below the opening of the chimney.
The female swift lays a clutch of four eggs over a period of seven to eight days. The parents share incubation duties for about 19 days until the eggs hatch.
Young swifts start climbing the wall near the nest about 19 days after hatching, but their first flight comes about 30 days after hatching.
Invariably, a few tumble into the fireplace and end up in the house. So if you don’t want that maiden flight in your living room, get your chimney capped soon.
Thanks to the extended nesting period, swifts in the temperate latitudes nest only once each year. And though you may see dozens or even hundreds of swifts return to a chimney at dusk, they are not colonial nesters.
Usually just a few pairs nest in a chimney; the rest are non breeders using the structure to roost.
As more and more people cap their chimneys to keep swifts and other wildlife out of their homes, swifts find it increasingly difficult to locate nesting sites.
Some might return to hollow trees and caves, but a group in Texas has had great success with artificial chimneys. They’re based on a design developed in 1915 by Althea Sherman, whose observations remain the foundation of our understanding of chimney swift nesting biology.
To learn more about chimney swifts, including how to build an artificial chimney, visit the above Web site.
An artificial chimney, which must be at least 8-feet tall, is a major project that requires a concrete foundation, but researchers report most are used by swifts the first nesting season they’re available.
I encourage readers to visit my Web site regularly (http://scottshalaway.googlepages.com). I’ve added many new features recently. You’ll find a collection of archived columns as well as links to my e-mail address, migration maps, spectacular photographs and live web cams set up at nests of a variety of birds. Check in every week to see what’s new.