CLIFF  SWALLOWS:  FAITHFUL  AS   MATES,  MIGRANTS,  AND  MUD-MASONS

Dr. James J. S. Johnson

Thine own friend, and thy father’s friend, forsake not; neither go into thy brother’s house in the day of thy calamity: for better is a neighbor that is near than a brother far off.  (Proverbs 27:10)

Alongside a rocky hillside outcropping, or under a montane cliff overhang, the mud-home “condominiums” of the Cliff Swallow (Petrochelidon pyrrhonota) reveal the presence of this gregarious and aerial-acrobatic bug-eater.

CLIFF SWALLOW inside mud-nest

National Park Service photo / public domain

On June 29^th of AD1996, by Colter Bay Village Marina, in Grand Tetons National Park (Wyoming), I saw some of these, and considered how their colonial nests reminded me of the riparian (i.e., riverbank) Bank Swallow (Riparia riparia) burrows that I had seen (2 days earlier) along banks of the Snake River.

Like other swallows, the Cliff Swallow speedily zips and arcs and dives through the air, snatching and consuming many “meals on wings” – veritable “fast food” – gulping down airborne insects, again and again.  (The Cliff Swallow supplements its insectivorous diet with berries and other fruits.)

However, the Cliff Swallow’s claim to fame is their colonial mud-home masonry.

“Hundreds of gourd-shaped “mud jugs” plastered to the side of a barn or under a bridge or highway overpass are a typical [colonial] nesting territory for these highly adaptable birds. Farmers heartily welcome this [summer] resident because it eats numerous flying insects that are harmful to crops. Nesting colonies may number from 800 to more than 1,000 birds. Note the dark rusty brown throat, and in flight the brown underwing linings, cinnamon buff rump, [characteristic] square tail, dusky cinnamon undertail coverts with dark centers, and whitish buff edged feathers of back and tertials. Juveniles have dusky brown upperparts and paler underparts. This [bluish-brown-black-backed] swallow has successfully expanded its range in the [American] Southwest and the West. The southwestern race [i.e., variety] displays a cinnamon forehead similar to the Cave Swallow.”

[Quoting Frederick J. Alsop III, BIRDS OF TEXAS (Smithsonian Handbooks, 2002), page 363.]  Cliff Swallows closely resemble Cave Swallows (Petrochelidon fulca), but Cave Swallows have a “pale cinnamon-buff throat”, cinnamon-rust-hued throat, and a “richer cinnamon-rust rump”, according to Alsop [at page 363].  Another similar-looking swallow is the deeply-forked-tailed Barn Swallow (Hirundo rustica) which often colonizes the inside of rural barns (as well as in places where Cliff Swallows build nests) all over America’s Lower 48 states.

In fact, these 3 varieties of swallows — Cliff Swallow, Cave Swallow, and Barn Swallow – are known to hybridize, so there is no need to fret over which species name you assign to one of these swallows.   [For documented examples of these mud-homebuilding swallow hybridizations, as well as many other swallow and martin hybridizations, see Dr. Eugene M. McCarthy’s HANDBOOK OF AVIAN HYBRIDS OF THE WORLD (Oxford University Press, 2006), pages 253-255.]

Other forms of “hybrid” mixing occur, involving other types of social interaction, such as the neighborliness known as “helping”:

“NEST HELPERS occur among many species, including certain kingfishers, hawks, jays, tanagers, and wrens. Helpers are generally younger adults that assist their parents in rearing nestlings. . . . Helpers generally do all of the usual nest-associated behaviors, such as building nests, incubating eggs, guarding nestlings, cleaning the nest, and feeding young. With such help, it’s not surprising that several studies have shown that [parental] pairs with nest helpers can rear more young than those without helpers. . . . While most helpers assist their parents [with the care of younger siblings], there are also many examples of adults feeding young of different species. Parent Barn Swallows may, for example, feed fledgling Cliff Swallows. Robins have been known to feed young grackles.”

[Quoting Stephen W. Kress, BIRD LIFE: A GUIDE TO THE BEHAVIOR AND BIOLOGY OF BIRDS (Racine:  Golden Press, 1991), page 54, with emphasis added.]

CLIFF SWALLOW on mud-home nest

Photo credit: What-When-How.com Tutorials

The Cliff Swallow takes all of its social relationships seriously – they are characteristically monogamous, sometimes rearing 2 broods in one breeding season, and they live gregariously in large colonies. [See Stan Tekiela, BIRDS OF TEXAS FIELD GUIDE (Adventure Publications, 2004), page 125.]  Also, they share information about where to get food.  When some of these swallows observe other fellow-colonist swallows returning with food for their young, indicating the successful sourcing of food, those watching follow suit, following the “winners” to the place where food is readily available.

Professor Alsop describes the Cliff Swallow’s homebuilding hallmark as the construction of “one of the most complex swallow nests: a sphere of mud pellets with a tubular entrance on one side”.  [Quoting Alsop, BIRDS OF TEXAS, cited above, page 363.]  Unsurprisingly, Cliff Swallow nesting colonies are located near water, since water is needed by both the swallows and their insect prey.  Little mud-balls used for nest-building, carried serially during nest construction, may be acquired from mud sources a mile away.

CLIFF SWALLOWS acquiring mud for nest-building

Photo credit: Cameron Rognan / Flickr

These swallows migrate, breeding all over Texas, often returning each spring to last year’s nesting sites. In fact, Cliff Sparrow migratory punctuality is famous:

“THE TIMING OF MIGRATION is [phenologically] linked to the length of day [i.e., daylight hours]. As day-length increases with the advancing spring [season], birds develop a nocturnal restlessness called “zugunruhe” [from 2 German words meaning move/migration and anxiety/restlessness]. Increased exposure to daylight leads males and females to higher hormone levels that trigger the urge to migrate [northward from South America]. Migration becomes a predictable event. Cliff Swallows of San Juan Capistrano Mission in southern California and Turkey Vultures of Hinkley, Ohio [not to be confused with Hinckley, Minnesota – “where the men are men, pansies are flowers, and the women are slightly above average”] , are noted for their punctual spring arrivals. The spring arrivals of many backyard birds, such as American Robins and Red-winged Blackbirds are equally punctual.”

[Quoting Stephen W. Kress, BIRD LIFE: A GUIDE TO THE BEHAVIOR AND BIOLOGY OF BIRDS (Racine:  Golden Press, 1991), page 108.  Regarding zugunruhe and photoperiod analysis, see Eberhard Gwinner, “Circannual Rhythms in Bird Migration”, Annual Review of Ecology & Systematics, 8(1):381-404 (1977), posted at http://www.annualreviews.org/doi/10.1146/annurev.es.08.110177.002121 — with an acknowledgement that “internal annual clocks” had been demonstrated earlier in hibernating Golden-mantled Ground Squirrels.]

Like other swallows, the Cliff Swallow speedily eats many “meals on wings”  –  veritable “fast food”  –  catching and eating insects in the air.  The Cliff Swallow supplements its insectivorous diet with berries and other fruits.

Thus, the Cliff Swallow is faithful in mating (i.e., avian “marriage” and parenting), faithful in migrating (i.e., in the phenological punctuality of its spring migrations), and faithful in its mud-home masonry tradition. Cliff Swallows are famous for sharing and living together in harmony – like good neighbors.

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