October 20, 2017
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Where did barn swallows live before barns were invented?

By Bob Duchesne, Special to the BDN

I keep my brain agile by pondering questions like: “Where did barn swallows nest before barns?” As it turns out, the answer is caves. But once humans started erecting barns, the birds quickly adopted them, and now the barn swallow is the most abundant species of swallow in the world. It nests throughout North America, in all places except southern Florida and the desert southwest. Barn swallows also range across most of the Old World, just about any place there are buildings.

Our barn swallows will be leaving soon. They are long distance migrants, with a wintering range throughout South America, all the way down to the southern tip of the continent. It’s a little sad to think that our fall migration is already about to begin, but when birds make a living by snatching bugs from the air, they can take their time traveling southward. There’s bugs the whole way.

Insects aren’t declining, but barns sure are. With fewer places to call home, barn swallow populations have waned by half in the last 50 years. Nonetheless, the remaining swallows are doing well enough and their numbers are not considered worrisome.

Barn swallows are a deep shade of blue, with a lovely tinge of orange through the face and throat, making them attractive enough for adornment and small enough to mount on hats. That’s exactly what happened in the late 1800s when putting birds on hats was the fashion rage. Long before America’s population of wading birds was being slaughtered for their plumes, the rampant annihilation of barn swallows raised concerns, sparking the first outcries for conservation and founding of the first Audubon Society.

Normally, a bird that nests among humans and poops indiscriminately might be considered a nuisance. But the barn swallow’s propensity for devouring pests has contributed to its popularity. It’s a rare farmer who doesn’t appreciate the reduction of insects around the cowshed. Barn swallows are considered good luck in many societies, and superstitions abound about what can go wrong with your milk cow if you hurt the swallow nests.

Barn swallows live on the wing, swooping through fields and open areas, nimbly snatching anything that flies. They prefer larger insects, such as beetles, butterflies, moths, and wasps, leaving the mosquitoes and black flies to others. Since larger insects tend to be closer to the ground, barn swallows often forage lower than other swallows, sometimes just inches above the surface. Barn swallows even drink and bathe on the wing, dipping into ponds while flying.

The tail of a barn swallow is much more deeply forked than the tails of other swallows. It aids in their aerial acrobatics. But it also signifies mating superiority. Studies show that swallows of both genders choose mates with longer tails. Apparently tail length is a sign of overall health, chick-rearing ability, and resistance to parasites.

Longer tails also correlate with the likelihood that the swallow will fool around with other swallows when the mate isn’t looking. Although pairs are socially monogamous and mate for life, extra-pair copulations are common. Males are aggressive in protecting their mates from rivals, but opportunistic in the presence of an unguarded female of another pair. It’s complicated.

Pre-human swallows probably didn’t cluster in caves while nesting, but when the birds switched to barns, they evolved a tendency to form colonies. Groups of swallows build their mud nests under the eaves of a barn or beams of a bridge. Since they are mostly unconcerned about people, naturalists have had an easy opportunity to study their social dynamics.

Each male defends a small territory around his nest, and he will chase off and even grapple with any interloper. Sometimes, an unmated juvenile from last year’s brood will help the parents raise this year’s clutch. Even unrelated birds may assist. After all, you can never be too sure who your father is. Conversely, unmated males have been known to kill nestlings in a nearby nest in hopes of breaking up the couple and stealing a bride.

Swallows cooperate in driving off threats, aggressively driving off cats, jays, crows, and hawks.

Barn swallows don’t visit bird feeders, but they will consume ground up eggshells or oyster shells. Leaving shell grit on a platform feeder provides a source of entertainment for you and calcium for them. I’m told it works. I’ve never tried it.

So much for today’s question. My next question to ponder: Whose ironic idea was it to put a hyphen in the word non-hyphenated?

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.


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