Above: a nestling swift in the Silver Basin in the San Juans

The Black Swift:
mystery bird of the Rockies

Researchers and volunteers study this elusive colonist

By Rich Levad

A small, black, boomerang-shaped form, barely visible against the darkening sky, sweeps past the two observers. One shouts over the roar of the waterfall, “Did you see that? Was that a swift?” Then another dark form zips past, in view for only a split second. The observers snap their eyes to the falls just in time to see the bird swoop under a mossy overhang and disappear. “Yes! Wow! Are they fast! If I had blinked, I would have missed it!” The pair grin, exchange a high five, and congratulate each other on their discovery: a new Black Swift colony.

This sceneÑor scenes very similar, has been repeated nearly fifty times in the past three years as researchers from the U.S. Forest Service and Rocky Mountain Bird Observatory (RMBO) have explored Colorado’s waterfalls, searching for evidence of occupation by this strange, mysterious bird. The search has involved well over 1,000 miles of hiking with close to 100 miles of elevation gain, a good deal of that mileage achieved by bushwhacking up trailless creek bottoms.

Elusive and Unusual

The Black Swift’s habits make it a difficult bird to find. It usually builds its nest in a shaded niche where its dark plumage merges into the shadows. As Kim Potter, a biologist with the White River National Forest and one of the leaders in the current search quips, “They put their nests where the sun don’t shine.” The chosen niches are in locations invariably inaccessible and usually invisible to predators, including humans. They are typically protected from above by an overhang, which shades the nest and hides it from hawks and owls soaring above, and from below by sheer, wet cliffs, which no terrestrial predator could climb without putting its life in jeopardy.

In their mountain haunts, Black Swift nests are built almost entirely of moss, a material usually in good supply in the vicinity of waterfalls. The availability of moss is one explanation that is advanced to explain the bird’s affinity for these sites. Well protected from weather in their hidden niches, the nests persist through the winter and are often used for several years. Swifts seem uninterested in constructing new nests if an old one is available; they simply add a small amount of moss to the top and move in. This additional moss appears as a green fringe on top of the old reddish-brown nest and serves for some time as a clear indication that the nest has been used. Early in the breeding season, an empty nest with a green fringe can be an indication of a nest attempt that failed.

Above: a waterfall on Fall Creek that houses a population of Black Swifts behind the water

A notable exception to the odd pattern of nesting at waterfalls is even stranger: one colony of Black Swifts resides in a resurgence cave deep in the Flat Tops wilderness area, building nests as much as seventy feet back from the cave’s entrance. Discovered in 1962 by Donald Davis, one of Colorado’s premier spelunkers, this site went unvisited for more than 35 years until Davis guided a crew of Forest Service, Colorado Division of Wildlife, and RMBO field workers to the cave in early September 1998.  The group was delighted to find six nests in the cave, all occupied by young swifts. All of the six nests were occupied when the site was visited in each of the following two years.

Swift biology is unusual. Each pair of Black Swifts lays a single egg, which is three times larger than that of its only slightly smaller cousin, the White-throated Swift. The eggs incubate for approximately four weeks, a period twice as long as that of most birds its size. The nestling does not leave home until it is about 45 days old, much later than other birds of similar size. Bluebirds and Robins, for example, incubate their eggs for about 13 days, and the young-sters leave the nest at 14 days of ageÑrather typical periods for birds that weigh in at two to four ounces.

In the first two weeks after hatching, nestlings develop a dense, downy covering that enables them to regulate their temperature. At this point, brooding by an adult is no longer required, and both parents leave the young birds early in the morning to spend the daylight hours foraging high above the peaks. Flying ants serve as the staple food for Black Swifts while they raise their young. These ants nest in coniferous forests, and in August when their populations peak, they disperse to establish new colonies. While dispersing, the ants sail over the peaks of the Rockies and form large clouds of Swift food. Although Black Swifts eat a variety of insects at other times, analysis of droppings at the nests shows that ants dominate the nestlings’ diet. Ants are an energy-rich foodÑ40% fat and 7% glycogenÑwith six times the energy content of flies, but they are widely dispersed and finding them requires long searches.

These searches are relatively easy for Black Swifts, who are superbly adapted to life in the air. They are among the fastest of birds and can attain speeds rivaling those of stooping falcons. They spend most of their lives riding the air on long, narrow, swept-back wings. Besides eating, they perform most of their other important life functions on the wing as well, including courtship and perhaps even copulation.

On their daily foraging flights, they cover hundreds of miles and soar so high that they appear only as tiny specks in the sky, earning them the nickname, “Cloud Swift.” They forage for sixteen hours or more, gathering a bolus of ants in a pouch at the back of their throats. In the evening, after the sun has set, the adults return to their nests and feed the waiting youngster throughout the night.

While the adults are out foraging, youngsters may slip into a state of torpor with a drastically reduced metabolism rate that enables them to go sixteen hours or more without food. Some researchers have suggested that the cooling effect of the waterfall’s spray may enhance this ability. No other North American land bird is known to employ this strategy, but a number of seabirds in the family AlcidaeÑthe auks and puffinsÑalso leave single youngsters at home in torpor for long periods while they gather food.

Because Black Swifts don’t arrive in the Colorado Rockies until early June, their extended nesting period means that most fledglings can’t leave the nest until September, and the very latest may not depart until early October when most other insectivorous birds have been back in the tropics for a month or more. The youngsters have to be ready to travel as soon as they can fly; their maiden flight appears to be the migration flight. No young swift has ever been seen at its colony site once it flies off the nest. The youngsters prepare for this flight by exercising their wings on the nest during the last couple of weeks of their development, a habit that makes this a prime time to find the nests. The precise destination of this flight, described in the most current literature as “somewhere in South America,” is still unknown.

The breeding range of the Black Swift is as odd as its nesting habits, consisting of several widely separated patches. What may be the largest concentration of nests in the Northern Rockies and Cascade Mountains ranges from Washington to Montana along the Canadian border, northward through Alberta and British Columbia, and just into the southeastern tip of Alaska. Large flocks are sometimes seen over the lakes of this region, but fewer than a dozen colony nesting sites have been located. Black Swifts also breed in the mountains of western Mexico and Central America, and they are year-round residents in Cuba, Jamaica, and Hispaniola. In the western United States, widely scattered colonies have been located in California (a dozen or so), Arizona (1), New Mexico (1), and Utah (4). Although Yellowstone and Teton National Parks both have a number of spectacular waterfalls, no Black Swift colonies have yet been found in Wyoming. Some colonies are hundreds of miles from their closest neighbor, so reports of possible Black Swifts in any area that has waterfalls should not be discounted quickly, regardless of how unlikely they might seem.

Studying Black Swifts in Colorado

In Colorado, the San Juan Mountains host the largest number of Black Swifts, and most of the waterfalls in the vicinity of Ouray, Telluride, and Silverton are occupied. Many of the waterfalls on the streams tumbling off of the edges the Flat Tops north of Glenwood Springs, such as Bridal Veil Falls at Hanging Lake, play host to colonies, as do several falls in Rocky Mountain National Park and a few in the Sangre de Cristo Mountains.

Black Swifts are considered colonial birds, but their colonies are quite small, averaging only three or four pairs. RMBO researchers estimate that Colorado hosts approximately 100–125 such colonies, so the total population for the state may not exceed a thousand birds. This relatively small number, however, is estimated to be as much as 10–20 percent of the species’ world population. Because of its limited numbers, the Black Swift is considered a “sensitive species” by the Regional Office of the U.S. Forest Service, and as such has received a lot of attention from the Monitoring Colorado’s Birds (MCB) program, which is conducted by RMBO for the state’s wildlife and land management agencies.

Prior to the initiation of the current search in 1998, fewer than 35 Black Swift colonies had been located in Colorado, most by the pioneering researcher Owen Knorr back in the early 1950s. Knorr’s achievement has been an inspiration to the MCB teamÑalthough they cringe at the photos of him and his associates rappelling into nest sites. Knorr, now retired from a career as a university administrator, continues to advise the searchers. Most of his early sites have been re-found in the current search. This effort was complicated by the circumstances that most of his original notes were lost and that site descriptions in his published data were deliberately vague because egg collecting had not completely died by the middle of the twentieth century. A 1922 price list valued a Black Swift egg at $75Ñmore than triple the next highest priced egg, and an “egger” had approached Knorr with an offer soon after the account of his initial discovery was published, so he was hesitant to publish precise details on the location of his sites.

The MCB search has raised the number of known colonies to 88, a total far exceeding that of any other state, and greater than that of all other areas combined. Other states may host as many swifts, but none has located many more than a dozen colonies. California has the second largest collection of known sites. Some of the California Black Swifts nest in sea caves where they construct nests of mud, a strikingly different pattern from that of the mountain dwellers. The different patterns do share the characteristics of being dusky and dank, which seem to be requirements for Black Swift residences.

The first step in current search involved creating a database of Colorado’s waterfalls. Those described in Marc Conly’s Waterfalls of Colorado were entered first, followed by those found by searching topographic maps for additional falls. As the project proceeded, field workers regularly stumbled upon previously unknown waterfalls, and the database has reached more than 350 entries. During the past four field seasons, observers have visited more than 275 of these falls, searching for evidence of occupancy by Black Swifts, and evaluating the sites on their suitability for the birds. The visits include a search for nests and a ranking of each site, using a scale based on Black Swift nesting requirements designed by Chris Schultz, a biologist with the San Juan National Forest and one of the initiators and major participants in the search. Finally, the observers conduct an evening watch to see if any adults arrive. Frequently, a quick glimpse of swifts a moment before it becomes too dark to see them is the only evidence of the existence of a colony. Knorr found in his work that during the breeding season, the birds nest where they roost. By rappelling off the cliffs into the nesting areas, he was eventually able to find nests at every site where he saw birds coming to roost. The current search has located a number of roost sites where nests have not yet been located, but based on Knorr’s extensive experience, the project leaders are confident that the nests are there.

In the summer of 2003, the researchers hope to complete the task of evaluating falls. Once it has been completed, they will design a monitoring program to track the state’s Black Swift population. At the present time, it seems likely that this program will consist of some combination of nest checks and evening watches. The nests that can be seen without serious technical climbing will be checked for occupation, and the adults returning to feed the young at dusk will be counted.

The value of volunteers

The research effort has been greatly assisted by the contributions of a small corps of dedicated volunteers. These folks have entered data, accompanied the field workers on journeys to waterfalls (for safety, the protocol calls for visits to be conducted by at least two persons), and have discovered a number of new colonies themselves. More volunteers are being sought for searching for nests at roost sites, and for the monitoring program that will follow.  The monitoring program will be a part of RMBO’s Project ColonyWatch, a program that engages in monitoring all of Colorado’s colonially-nesting birds.

The level of effort required for monitoring will vary from site to site. Some Black Swift nesting sites are at popular roadside tourist falls such as Rifle Falls, Treasure Falls near the foot of Wolf Creek Pass, Bridal Veil Falls in Telluride, and Box Canyon Falls in Ouray, all of which are easily accessible; most, however, require some hiking, and a few are accessible only by some rock climbing. The project leaders are particularly interested in enrolling volunteers with the skill and equipment to monitor especially inaccessible nest sites.

A training day for volunteers will be held on Sunday, June 30, at Ouray. After a brief orientation, participants will visit Black Swift colonies at Box Canyon Falls, Cascade Falls, and at several falls along Canyon Creek. Anyone interesting in joining this effort can enroll by contacting the author, Rich Levad, at (970) 241-4674 or by e-mail at rich.levad@rmbo.org. P

Rich Levad is Special Monitoring Projects Coordinator for the Rocky Mountain Bird Observatory. He can be contacted through www.rmbo.org.