Go out on any fall day when there are insects buzzing about, and you’ll see a unit of feathered fighter jets swooping and diving after them. These avian aerialists—swifts and swallows—may look similar and exploit the same niche, but they’re not related at all. They only resemble each other because of convergent evolution, which means they’ve developed some of the same physical traits to adapt to their shared environment.
So how does the enterprising birder tell them apart? By paying attention to details and behavior.
First, check the color. Flashes of blue, green, orange, or iridescence are characteristic of swallows. Swifts are mostly soft gray. There are a few exceptions to this rule, however: The White-throated Swift has a chalky belly, while Northern Rough-winged and Bank Swallows are brown overall.
While you’re at it, study the subject’s wings, too. Are they uniformly long, skinny, and fluttering? That’s a swift. Are they relatively thick near the body and then tapering? That’s a swallow.
The nest can also be a good distinguisher. If it looks like a hunk of sticks attached to the side of a vertical surface, it likely belongs to a swift. Members of the family Apodidae use saliva to glue their nests together above ground. Swallows, on the other hand, will use either smeared-mud chambers (Barn and Cliff), a trunk cavity (Tree), or holes dug into dirt bluffs (Bank).
Other strong signs include foraging and lounging behavior. Swifts fly in the upper part of the air column as they hunt; swallows pursue insects closer to the ground or water. If the bird is perched on a nest box, power line, or branch, that’s a giveaway: Only swallows have the wherewithal to sit upright. Swifts are just stage-five clingers.
But the most obvious clue is a combination of time and place. If the sun is setting and the bird is dipping into a chimney, then the matter is settled. It’s a swift. Or a bat.
For more quick-reference tips on swifts and swallows, listen to the short BirdNote podcast below. BirdNote is a partner of The National Audubon Society; its episodes air daily on public radio stations nationwide.
Written by Bob Sundstrom
Producer: John Kessler
Managing Producer: Jason Saul
Associate Producer: Ellen Blackstone
Bird sounds provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. 66813 recorded by William W. H. Gunn, 223902 recorded by Peter Paul Kellogg and Karm Parker, and 84826 recorded by Wilbur L. Hershberger.
BirdNote’s theme music was composed and played by Nancy Rumbel and John Kessler.
© 2017 Tune In to Nature.org July/August 2017 ID# swallow-swift-01-2017-08-17 swallow-swift-01