Avian Architects Setting Up Shop

They typically nest in large colonies, occasionally numbering in the thousands.  Within these noisy, chattering colonies, they push “neighborliness” to the limit, laying eggs in or even moving their eggs into their neighbors’ nests.  They recognize the voices of their offspring even among thousands of other kids squawking to be fed.  They spy on their neighbors to figure out where the best insect swarms are.  Who are these extremely sociable birds of North America?  Cliff Swallows!


Originally birds of the western mountains, communities of Cliff Swallows nested in the steep canyons and lower elevations of the massive mountain ranges.  During the past century or so, though, they expanded their breeding range across most of North America, following close on the heels of the construction of highways and bridges that now provide potential nesting sites as well.


In low light, a Cliff Swallow (affectionately known as a “Cliffie”) looks brown with light underparts, a buffy rump patch (called upper tail coverts), and a squared-off tail.  Good light reveals its lovely metallic blue-black back and shoulders and a sharply defined chestnut-colored throat.  With a pale strip on its forehead, it somewhat resembles a chunky bird sporting a headlamp.  Males and females look alike as they swoop by you.  But juvenile birds show extremely varied colors and degrees of white speckling on their throats and foreheads—greater variation in juvenal plumage than any other species in North America.


The Cliffie’s scientific name, Petrochelidon pyrrhonota, refers to both its nesting preferences and its colorful rump patch.  Petrochelidon means “rock swallow” (from petros, Greek for “stone or rock,” and khelidon, Greek for “swallow”).  The species name, pyrrhonota, means “flame-colored back,” from purrhos (“flame”), and noton (“back”).  The common name of “swallow” comes from the Anglo-Saxon swalewe, used for this group of birds; “cliff” again recalls the species’ historical preference for nesting sites.


Cliff Swallows return to California in mid-February to early March to set up housekeeping.  Their nests are unmistakable—gourd-shaped bowls covered with mud pellets, attached to a vertical surface, with small entrance tunnels.  The birds usually build their nests under an overhang, to escape heavy rains (disastrous for any mud home!).  Both males and females help with construction; they often tuck their nests in corners and tight against neighboring nests, minimizing the amount of mud needed to cover the nest.  These birds return to successful sites year after year, refurbishing old nests as needed.  You’ve heard of the swallows that used to return to the mission at San Juan Capistrano every year?  Yep—they were Cliffies.


All in all, you could say that flight equals life for these aerialists.  Cliff Swallows drink exclusively on the wing, lightly skimming the surfaces of lakes and rivers with their beaks.  They rely on swarming insects, hunting sometimes as high as 150 feet above land.  To be prepared for this airborne life, a clutch of 1 – 6 nestlings remains in the nest quite a long time, compared to most songbirds—20 – 26 days after hatching, compared with 10 – 15 days for many other songbirds.  These extra days in the nest help to develop strong flight muscles, so that Cliffies are pretty decent flyers as soon as they fledge.  The parents help the fledglings for about a week after they leave the nest, teaching the youngsters to catch insects for themselves and launching them into their own, independent lives on the wing.  Their numbers drop rapidly in early September, as nearly the entire population heads to South America for the winter.


These birds provide a wonderful service of insect control for the planet.  Consider breeding season alone.  The adults together make up to 18 visits to a nest per hour during daylight hours.  Assume 14 hours of daylight during the time they’re nesting.  An adult can deliver a “serving” as large as 0.8 grams of insects scooped up and compressed in its throat.  Kids stay in the nest for at least 20 days (and often longer) and the parents continue to feed them for another 5 days once they fledge.  Let’s do the arithmetic:  18 * 14* 0.8 * 25 = 5,040 grams.  So each nesting pair can remove as many as 5 kilos of insects each breeding season—and that doesn’t count what they themselves devour.  Unfortunately, swallows don’t eat many mosquitoes because mosquitoes fly primarily at dawn and dusk, rather than during daylight hours, when swallows forage.  But Cliff Swallows do eat lots of bees, wasps, aphids, planthoppers, flies, beetles and just about any other insects that concentrate in aerial swarms.


As mentioned earlier, Cliff Swallows rank among the most sociable species of birds in North America.  In addition to nesting in colonies, they forage collectively.  Fledgling Cliffies congregate in large groups called crèches.   And even when grown, Cliff Swallows hang out with their fellow swallows.  You can often spot them spaced as closely as 4” apart on a wire—and sometimes even closer, with their shoulders actually touching.  When you’re a Cliffie, you’re never alone.

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