CLIFF SWALLOWS: Faithful as Mates, Migrants, and Mud-home Masons

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.

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CLIFF SWALLOW inside mud-nest

National Park Service photo / public domain

On June 29th 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.]

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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.

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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.

><> JJSJ   profjjsj@aol.com

Shorebirds Looney about Horseshoe Crab Eggs

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Red Knot Eating Crab Eggs at Delaware Bay Beach

Photo by Gregory Breese / USF&WS

Thankfully, the rhythms of our world are fairly predictable. Although the details differ, the overall cycles are regular:

While the earth remains, seedtimes and harvest, and cold and heat, and summer and winter, and day and night shall not cease. (Genesis 8:22)

Because of these recurring patterns migratory birds can depend on food being conveniently available when they migrate northward in the spring. In effect,  “fast food” on the beach is a “convenience store” for famished feathered fliers.

For example, consider how the annual egg-laying (and egg-burying) activities of horseshoe crabs perfectly synchronize with the hunger of migratory shorebirds (e.g., red knots, turnstones, and sandpipers) that stopover on bayside beaches, for “fast food”, right where huge piles of crab eggs have just been deposited (and where some have been uncovered by tidewaters).

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Horseshoe Crabs on Delaware Bay Beach

Photo by Gregory Breese / USF&WS

No need to worry about the birds eating too many crab eggs! – the egg-laying is so prolific (i.e., about 100,000 eggs per mother) that many horseshoe crab eggs are missed by the migratory birds, thus becoming the next generation of horseshoe crabs, plus the birds mostly eat the prematurely  surfacing eggs that are less likely to succeed in life anyway!)

Timing is everything. Each spring, shorebirds migrate from wintering grounds in South America to breeding grounds in the Arctic. These birds have some of the longest migrations known. Delaware Bay is the prime stopover site and the birds’ stop coincides with horseshoe crab spawning. Shorebirds like the red knot, ruddy turnstone and semipalmated sandpiper, as well as many others, rely on horseshoe crab eggs to replenish their energy reserves before heading to their Arctic nesting grounds.  The birds arrive in the Arctic before insects emerge. This means that they must leave Delaware Bay with enough energy reserves to make the trip to the Arctic and survive without food until well after they have laid their eggs. If they have not accumulated enough fat reserves at the bay, they may not be able to breed.

The world’s largest spawning population of horseshoe crabs occurs in Delaware Bay. During high tide, horseshoe crabs migrate from deep water to beaches to spawn. The female digs a nest in the sand and deposits between 4,000 and 30,000 eggs that the male will fertilize with sperm. A single crab may lay 100,000 eggs or more during a season. Horseshoe crab spawning begins in late April and runs through mid-August, although peak spawning in the mid-Atlantic takes place May 1 through the first week of June.

At low tide, adult crabs go back into the water but may return at the next high tide. Horseshoe crab spawning increases on nights with a full or new moon, when gravity is stronger and high tides are even higher. At the same time that migrating shorebirds arrive to rest and feed along Delaware Bay, horseshoe crab activity is high. While the crab buries its eggs deeper than shorebirds can reach, waves and other horseshoe crabs expose large numbers of eggs. These surface eggs will not survive, but they provide food for many animals. The shorebirds can easily feed on eggs that have surfaced prematurely.

Quoting Kathy Reshetiloff, “Migratory Birds Shore Up Appetites on Horseshoe Crab Eggs”, THE CHESAPEAKE BAY JOURNAL, 27(3):40 (May 2017).

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Shorebirds and Horseshoe Crabs on Delaware Bay Beach

Photo by Larry Niles

Notice how it is the gravitational pull of the moon, as the moon goes through its periodic cycle, that causes the high and low tides – which facilitate the uncovering of enough horseshoe crab eggs to satisfy the needs of the migratory stopover shorebirds that pass through Delaware Bay.  Notice how the moon provides a phenological “regulation” (i.e., the moon is physically ruling and correlating the interaction of the horseshoe crabs, the migratory shorebirds, and the bay’s tidewaters – in accordance with and illustrating Genesis 1:16-18).

At low tide, adult crabs go back into the water but may return at the next high tide. Horseshoe crab spawning increases on nights with a full or new moon, when gravity is stronger and high tides are even higher. At the same time that migrating shorebirds arrive to rest and feed along Delaware Bay, horseshoe crab activity is high.

Again quoting Kathy Reshetiloff, “Migratory Birds Shore Up Appetites on Horseshoe Crab Eggs”, THE CHESAPEAKE BAY JOURNAL, 27(3):40 (May 2017).

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Map of Red Knot Winter Ranges, Summer Breeding Range, & Migratory Stopovers
Map by The Nature Conservancy, adapted from USF&WS map

So, you might say that these reproducing Horseshoe Crabs, and the myriads of migratory shorebirds, share phenological calendars because they’re all looney.

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Red Knot on Beach, during Migratory Stopover
photo by The Nature Conservancy / M J Kilpatrick