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Sunday, June 22, 2008

In the Realm of the Black Swift

Earlier this month, I was privileged to co-lead an Institute for Field Ornithology workshop with Ted Floyd in the San Louis Valley of south-central Colorado. Our base of operations was the Medano-Zapata Ranch, a huge (~100,000 acre) preserve owned by The Nature Conservancy near Great Sand Dunes National Park. The ranch was fabulous, with a rustic-plush atmosphere, incredible views of the Great Sand Dunes & Sangre de Cristo Mountains, and fantastic birding on the grounds. The procession of meals was amazing, often featuring bison from the ranch, and there was always a deluxe line-up of snacks and beverages available in the dining room. Needless to say, if you get the chance to visit, I'd say to jump at the opportunity!!
My cabin, with the Great Sand Dunes to the north.
A typical dinner, this one with roast bison, spring greens, grilled corn, and a stuffed potato.

Evening birding on the ranch grounds with alpenglow on the Sangre de Cristo Mountains (aka "The Sangres")

As amazing as the ranch was, it was only our home base. Each day we set out to visit various habitats around the San Louis Valley (which is as big as the state of Connecticut), accumulating a highlight reel of valley specialty birds like Gunnison Sage Grouse, Snowy Plover, Chihuahuan Raven, and both Black-throated & Sage Sparrows. Then we would return to the ranch to clean up, eat some more, and have lectures and discussions before conking out for the night (unless it was an owling night...) We ended up with 136 species for the workshop, most studied well in the context of their habitats.
Brewer's Blackbird

Black-throated Sparrow


Young Great Horned Owls

Violet-green Swallow

Great Horned Owl at sunset

Song Sparrow

Yellow-headed Blackbird

For me, the highlight of the workshop was on the last morning, when we departed very early to drive and then hike up to Zapata Falls, just west of the ranch. Our quest was finding Black Swifts, a species with highly specialized nesting habitat requirements and correspondingly patchy distribution. In the central Rockies, these birds return to suitable alpine waterfalls where they build their nests behind the arching water or on nearby spray-soaked cliff walls. It is an amazingly harsh place to raise a chick- most nesting sites are shaded and constantly soaked by the cold snowmelt-fed waterfall splash. The swifts plaster their nest on a ledge or in a crevice or niche on the vertical or even overhanging wall, using mud and moss. Then an adult has to sit there, constantly damp, incubating the egg for an average of 26 days. If that wasn't enough, the chick is left alone nearly all day while the adults forage, typically miles and miles away from the nest, accumulating a bolus of aerial insects (typically flying ants) that they feed to the chick throughout the night. The chicks cope with the situation by lowering their metabolism and entering a torpid state during their parents' absence (close relatives of swifts, goatsuckers and hummingbirds can also enter torpid states to ride out periods of cold weather.) Much (most?) of what is known about Black Swift nesting behavior is from the dedicated work of Sue Hirshman, who monitors the colony at Box Canyon on the west side of Ouray, Colorado almost daily during the nesting season. She, along with Carolyn Gunn and Rich Levad, published a groundbreaking article about these cryptic birds in the Wilson Journal of Ornithology (119(4):678–685, 2007). Here's the abstract:
This study presents 11 years of nesting success and phenology data for Black Swifts (Cypseloides niger) at Box Canyon in Ouray, Colorado. Nest data were recorded on a near-daily basis for 160 nest attempts. Nesting success was 72% and mean and extreme dates of nesting events, including arrival, egg-laying, onset of incubation, hatching, and fledging are reported. On average, Black Swifts arrived on 13 June, egg laying started on 28 June, incubation started on 1 July, hatching occurred on 26 July, and fledging occurred on 13 September. The average incubation period was 26 days and the nestling phase was 48 days. In seven instances, a second egg appeared after loss of the first egg and, in one case, a third egg appeared. It was not possible to ascertain whether second or third eggs represented a renesting attempt or nest usurpation.
We were at the final approach to the falls as the sky was lightening when I spotted the first silhouetted darts streaking away from the mountain. As the sky brightened, more and more of the birds appeared, sometimes effortlessly blasting out beyond view over the valley out and other times circling above the outflow of Zapata Creek. At one point we had 26 of the birds gathered in a vocal whirling cyclone of inky speed, but as the sky brightened the crowd thinned out. By the time daylight reached us the swifts were gone, likely high above the Sangres gathering pelagic insects above the tundra. A few of us decided to see what the nesting site of the swifts was like, sacrificing dry boots to wade up the tumbling creek inside of a gorge cut by the falls. Around a final corner was the falls, plunging in an arc about 30 feet down and filling the air with mist. A big block of ice still clung to the wall across from the falls, a relict of the winter's build-up. I was far from warm, even in my layers of synthetic clothes, and I was only there for a few minutes. I can't imagine a chick weighing only a few grams sitting unprotected and unmoving for hours every day, bathed in the mist and never feeling the warmth of the sun until its first flight, but that is exactly what they do! These birds arrive in the state late (on average, 13 June at the Ouray study site) and depart early (average fledging on 13 September in Ouray.) In the intervening 9 months there is almost no certain knowledge of where these birds go or what they do- presumably, they migrate (perhaps non-stop) to somewhere in South America, although their route is unknown and their wintering sites remain undiscovered. Definitely these are high on my list of favorite birds, and I will always consider sharing time with Black Swifts to be a privilege and a highlight of my birding experiences.
Zapata Falls (photo by Nancy Hetrick)

Me entering the water-filled gorge- yeah, my feet are cold... (photo by Nancy Hetrick)

Nancy and Onica having an immersion experience in the lair of the Zapata Falls Black Swifts

Damp and chilly but smiling as we depart the mist-filled gorge!!

Black Swift photo composite at dawn, Zapata Falls, Colorado

1 comment:

Beverly said...

You always write such interesting pieces...but this was absolutely stunning! Thank you so much!