Friday, October 4, 2013

"Swallows Circling with Their Shimmering Sound"

Look up on a summer evening near any body of water in the Seattle area, and you're bound to see the silhouettes of swallows, swooping and swirling as they pursue insects.

Several species of swallows (as well as the even more aerial swifts) grace our area; the ones we saw in early summer this year at Marymoor Park were the iridescent slivers of sky called Tree Swallows.

Tree swallows are common across much of North America. They're named for their habit of nesting in tree cavities near water sources (including holes in stumps, causing them to be called Stump Sparrows in the past), though they'll avail themselves of birdhouses and similar sites. They've been known to nest in mailboxes and under eaves (the species was once known as the Eave Sparrow in some regions). Thomas Brewer, nineteenth-century doctor and ornithologist (of Brewer's Blackbird and Brewer's Sparrow fame) noted that he'd observed tree swallows nesting even in a "rude candle-box."

(Which apparently is just what it sounds like: a box for holding candles. It was made of wood with a sliding lid and was designed to keep mice from eating the candles. I guess some nineteenth-century farm child filched the box from the kitchen, carried it off to collect treasures, and then forgot all about it and left it outside, at the mercy of swallows in the real-estate market.)

Marymoor Park was apparently fresh out of rude candle-boxes, but they had plenty of plastic gourds and wooden pole-mounted boxes for swallows as well as purple martins to nest in.

The birds were in the thick of breeding season when we strolled through the park. That evening, every nest site seemed to have a vigilant bird, presumably the male, perched atop it.

They weren't the least bit disturbed by humans walking by; they knew people were unlikely to raid their homes. The animals preying on their eggs and young are far more likely to be raccoons, opossums, and snakes (and cats, which take adults as well as young).

Tree swallows have actually enjoyed a pretty good relationship with humans, despite such sorrows as human-caused habitat fragmentation, pollution, and knocking-down of nests with a broom when said nests are in inconvenient (to humans) locations.

Native Americans put up gourds for the insect-eating purple martin to nest in, which tree swallows eagerly claimed, too. European settlers followed suit and even built massive purple-martin houses with multiple entrances; when martins declined in numbers, tree swallows were quick to move in.

And according to Birds of America, published in 1936, the tree swallows certainly knew which side their bread was buttered on: "In some localities swallow boxes have been erected and are readily occupied. English Sparrows are very apt to try to drive the swallows out of the boxes.

"Sometimes they do, but the human proprietor can easily discourage the English sparrows. The swallows very readily learn that man is fighting the sparrows and have been known to call persistently when annoyed by English sparrows so that the man may hear them and come to the rescue."

Tree swallows are migratory birds. They're one of the earliest swallow species to arrive in the north in spring and one of the last to leave in the fall. Though they dine mainly on insects caught in flight, they also eat seeds and berries in a pinch, unlike other swallows.

The flickering, darting flight of tree swallows is beautiful to see, and if you pause and listen, you can hear their calls, a rain shower of liquid notes.

Ornithologist William Leon Dawson, writing in the 1920s, transcribed the refrain as "Sweetie kickup, sweetie kickup, sweetie sweetie kickup" (with a helpful "etc." added at the end). An Audubon guide of the 1940s depicts the bird's voice as "twitterings of a sweet, liquid quality, often run together into a rippling chatter."

This post's title comes from the poem "There Will Come Soft Rains" by Sara Teasdale, who writes of "swallows circling with their shimmering sound" in a post-apocalyptic world in which "Not one would mind, neither bird nor tree,/If mankind perished utterly."

Mankind, however, would certainly regret the loss of swallows. A diligent researcher once figured out that the tree swallow's cousin, the barn swallow, can eat 60 insects per hour, making for about 850 in one day or 25,000 in a month.

Certainly tree swallows must be swallowing similar numbers of insects, providing pest removal free of charge while asking for nothing more than the shelter of a rude candle-box.