Bristle-thighed Curlew

Numenius tahitiensis

Glen Tepke
  • SCOLOPACIDAE
  • Snipe, Sandpipers, Phalaropes, and allies
  • 10,000

Bristle-thighed Curlews are fascinating shorebirds that breed on inland tundra in a small area of western Alaska and winter on small tropical islands across a large expanse of the Pacific Ocean. These birds can be quite aggressive on both their breeding grounds and on their wintering grounds, where they sometimes employ rocks to crack open and feed upon seabird eggs. During the winter, Bristle-thighed Curlews undergo a molt that leaves them completely flightless, and thus extremely vulnerable to predation by introduced predators such as cats and dogs.

Identification
Bristle-thighed Curlews are medium-sized shorebirds with long, downcurved bills. They are quite similar to Whimbrels in terms of size, shape and appearance, with striking striped head patterns, brownish upperparts, streaked breasts, and pale blue-gray legs. Bristle-thighed Curlews, though, are more cinnamon-colored overall than Whimbrels, and have distinctive cinnamon patches on their rumps and uppertails. The species is exceedingly unlikely to be found outside its limited range.

Distribution and Population Trends
Bristle-thighed Curlews breed only in a limited area of western Alaska, on the lower Yukon River and the central Seward Peninsula. This species winters on a wide range of small islands in the South Pacific, including the Hawaiian Islands, the Mariana Islands, Micronesia, Fiji, Samoa, and French Polynesia.

Ecology
Although this species has been known to science since it was discovered in the South Pacific in 1769, Bristle-thighed Curlews' breeding grounds were not discovered until the 1940s. These birds are now known to nest on hilly, inland tundra at a few sites in western Alaska. Bristle-thighed Curlews nest on the ground, often placing their lined depressions directly beneath dwarf willow shrubs. A typical clutch includes four eggs, which are incubated by both sexes for about 25 days. Chicks leave the nest shortly after hatching and are capable of feeding themselves, although they do receive parental care, first from both adults, and later, from just the male. Adults are very defensive of both eggs and chicks, and will perform distraction displays and outright attacks on potential predators.

Following the breeding season, most Bristle-thighed Curlews congregate on the Yukon Delta, where they feed on berries, insects, and other food items in preparation for a non-stop, 2,500 mile flight to the Hawaiian Islands and other sites in the South Pacific. On their wintering grounds, these birds feed on crustaceans, snails, small fish, and the eggs of breeding seabirds. In order to crack the thick shells of large seabird eggs, the curlews sometimes employ rocks as tools, a rare occurrence in the bird world. There is one final aspect of Bristle-thighed Curlews' wintering ecology that makes them unique: they are the only shorebirds to have a completely flightless period during their molt.

Threats
Bristle-thighed Curlew's flightless molt strategy undoubtedly evolved long ago, in response to the absence of any mammalian predators on its Pacific island wintering grounds. With the establishment of humans on many of these islands, and the subsequent introduction of mammals, Bristle-thighed Curlews' flightless molt is now a major liability to the species. Introduced cats and dogs prey heavily on flightless curlews, resulting in what is believed to be a population decline for these birds. The prospect of future gold mining in Alaska represents a potential new threat to this species.

The U.S. Shorebird Conservation Plan lists Bristle-thighed Curlew as a "Species of High Concern," based on relative abundance, threats on non-breeding grounds, and breeding distribution. With an estimated population size of less than 10,000, this species can ill-afford to suffer significant population losses on a yearly basis on its wintering grounds. In addition, its reliance on a small area for breeding in western Alaska places it at high risk to potentially disruptive activities such as gold mining.

Conservation
Bristle-thighed Curlews' main migratory staging area in the fall, the Yukon River Delta, has been identified as a site in the Western Hemisphere Shorebird Reserve Network (http://www.manomet.org/WHSRN/Sitesmap.htm). In addition, a number of wintering and stop-over spots for this species are protected in the Hawaiian Islands National Wildlife Refuge.

What Can You Do?
U.S. National Wildlife Refuges provide essential habitat for Bristle-thighed Curlews, and a great number of other species throughout the U.S. and its territories. Unfortunately, the refuge system is often under-funded during the U.S. government's budgeting process. To learn more about how you can help gain much needed funding for U.S. National Wildlife Refuges, visit: http://www.audubon.org/campaign/refuge_report/

References
BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International.

BirdLife International (2006) Species factsheet: Numenius tahitiensis, Bristle-thighed Curlew http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3010&m=0

Brown, S., C. Hickey, B. Harrington, and R. Gill, eds. 2001. The U.S. Shorebird Conservation Plan, 2nd ed. Manomet Center for Conservation Sciences, Manomet, MA.

Hayman, P., J. Marchant, and T. Prater. 1986. Shorebirds, An Identification Guide. Houghton Mifflin
Company, Boston.

Kaufman, Kenn. 1996. Lives of North American Birds. Houghton Mifflin Company, New York.

Sibley, David A. 2000. The Sibley Guide to Birds. Alfred A. Knopf, New York.