by Frank Keim
Once back in the mid-1990’s I was picking blueberries above Marshall and a large sickle-billed bird flew over. It was making a bee-line south, probably in migration mode, and on a whim I thought I’d try something to get its attention. So I whistled, not any old whistle, mind you, but one of those age-old wolf whistles that one usually threw at a babe sauntering somewhere in an urban setting.
Next thing I knew the bird put on its brakes in mid-air, turned around, circled once, then set down on the tundra to see what I was. I continued to wolf-whistle, and the bird continued to gawk at me. At the time, I thought it was a Whimbrel, but now I am convinced it was a Bristle-thighed curlew, really curious about this two-legged creature on the ground making sounds similar to those his own species makes, especially in spring during the mating and nesting season.
This past July I saw and heard others flying overhead while I was in the Lower Yukon Delta Wildlife Refuge near Chevak helping with a climate change study. In the air I couldn’t have distinguished them from a Whimbrel, but the call was remarkably different, reminding me at times of that of the Black-bellied plover.
I only learned when I got home what a rare bird I had just experienced out on the Delta. According to the ornithologist John Terres, it was one of the last North American bird species whose nest and eggs remained undiscovered even into the mid-20th century. Only in 1948 did Alaskan schoolteacher and naturalist Henry Kyllingstad and David A. Allen discover the first nest, eggs and downy young close to a lake located about 20 miles north of the Yukon River community of Mountain Village. They were aided in their search by local Yup’ik villagers who told Kyllingstad they called it Ciivikaaq because of the sound it makes, “chiu-eet.” He also likened the call to “the well-known wolf-call heard on the city streets” and “is a close enough imitation of the call to bring the birds wheeling about your head.” So Kyllingstad had the same experience I did in Marshall.
While we’re on names, the bird’s common English name comes from the hair-like feathers on its flanks and thighs. And its scientific name, Numenius tahitiensis, means loosely, “Tahitian bird with the new crescent moon-shaped bill.” Tahitian, because it was first collected by scientists on the island of Tahiti in 1769. Tahiti is just one of the south Pacific islands where these curlews spend their winters.
Once they get back to Alaska from their warm winter sojourn in the South Seas, the Ciivikaat establish a nesting territory in the hilly tundra areas on the Lower Yukon River Delta. The male then begins his aerial display, flying repeatedly over the nesting area. As he soars then cruises around and around he first issues a number of wiitew notes followed by a liquid flowing almost haunting pidl WHIDyooooo whistle to let other males know about his and his mate’s claim to that part of the tundra. Their claim seems to be quite large, so it must also include the exclusive right to hunt there as well.
A nesting spot is chosen by the female, usually just a shallow depression in the tundra under a dwarf willow that she adds bits of lichen, moss and leaves to. Four brown-blotched olive-buff eggs are laid in the form of a cross, and are incubated by both adults until they hatch after about 25 days.
As with other shorebirds, Bristle-thighs are precocial, which means that when the young emerge from their shells they are already dressed in downy feathers and ready and rearing to leave the nest. Shortly after the last chick shucks its shells they all leave together and immediately begin feeding by themselves. Both parents continue to watch over them, however, and they all remain near the old nest site.
The adults are very aggressive both in defending the nest and the young, and like other shorebirds do a sort of “broken wing act” to lure predators away. They may even attack large predators such as a fox or wolf head-on. After a few days, the new family moves away from the nest site, eventually joining with other Bristle-thighed curlew families on neighboring tundra hilltops. The mother bird usually departs the scene before the young fledge, leaving her mate to fend for the young until they take their maiden flights and are fully on their own.
At the end of the nesting season, Bristle-thighs congregate on the Yukon Delta and gorge themselves on berries and insects, building up fat reserves for their long non-stop 2500 mile migratory flight to Tahiti and other south and mid-Pacific islands.
Once they reach their wintering grounds, they feed on crustaceans, snails, small fish and the eggs of breeding seabirds, including boobies, frigatebirds, terns and even albatrosses. They sometimes break the eggs of the smaller seabirds by taking them aloft in their bills and dropping them on hard sand. But when they feed on the thick-shelled eggs of albatrosses, they often use rocks as tools to crack open the shell. This is a rare case of tool using by a bird.
Something else extremely rare about Numenius tahitiensis is that it is the only shorebird anywhere to have a completely flightless molt. And not only does it do this, but it does so after it reaches its wintering grounds in the South Pacific. And since humans and their pets live on these islands, the birds are at their most vulnerable stage of development. No wonder their worldwide population is less than 10,000 birds!
Chiu-eet, chiu-eet, chiu-eet, chiu-eet, chiu-eet…
