Numenius tahitiensis

A large brownish shorebird with a moderately long decurved bill, striped head, and tawny unbarred rump. The stiff feathers on the thighs and flanks are not easily seen in the field (NGS 1983).

Differs from the Whimbrel (Numenius phaeopus) in being tawnier and by having a tawny unbarred rump, less streaking on the breast, and a paler bill. Bill is much shorter than that of Long-billed (Numenius americanus) and Far Eastern curlews (Numenius madagascariensis); longer, thicker, and more curved than in Eskimo Curlew (Numenius borealis); which averages 7 cm shorter).

Breeding: Breeding occurs in the low, mountainous regions northeast of the lower Yukon River (Nulato Hills) and uplands of the Seward Peninsula, Alaska (Handel and Dau 1988, Marks et al. 2002). Physiography differs markedly between Seward Peninsula and Nulato Hills; the latter is characterized by lower relief, gentler slopes, more complex drainage patterns, and smaller areas of specific habitats (Marks et al. 2002). Breeding areas encompass a mosaic of subarctic and arctic tundra habitats including: low shrub/tussock tundra (Betula nana, Empetrum nigrum, Ledum palustre, Vaccinium spp., Salix spp.), mixed shrub thicket/tundra (Salix spp., Betula nana, and Alnus crispa over tussocks), tall shrubs (Salix alexensis, typically along water courses), and shrub meadow/tundra (species similar to low shrub/tussock tundra but lower and with more bare ground). Sedge (Carex aquatilis, C. bigelowii), cottongrass (Eriophorum spp.) and lichen meadows, though a small fraction of the overall land area, are also important habitats.

Habitat use changes during the breeding season. During pre-nesting, curlews tend to be found primarily in shrub meadow/tundra (33%) and low shrub/tussock (47%); during nesting the birds shift their activities mostly to shrub meadow/tundra; and during brood rearing, adults attending young increase their use of sedge meadows. Younger broods tend to use habitats with a moderate level of tussocks and shrub cover; after fledging they prefer sedge and lichen meadows (Gill et al. 1990).

Foraging microhabitat: Foraging occurs primarily in dwarf-shrub meadow tundra on slopes and ridges, also in wetlands and medium-shrub (0.5-1.0 meters tall) habitats including marshy streambeds, stream shorelines, shallow lakes, moss or grass/sedge understory along margins (rarely interiors) of willow thickets, and lingonberry and Labrador tea (Ledum spp.) understory around dwarf birch thickets. On staging grounds, foraging birds are most common in tundra/meadow mosaic (Marks et al. 2002).

Staging: Staging prior to primary migration occurs on the coastal fringe of the Yukon-Kuskokwim Delta and coastal lowlands of the Seward Peninsula, Alaska. Staging habitats include sedge and graminoid meadows and upland tundra (Handel and Dau 1988). Annual variation in standing crop of fruits of black crowberry and ericaceous shrubs appears to be a major determinant of habitat use. Southward migrants on the central Yukon Delta roost at night in shallow brackish pond edges surrounded by large wet-sedge meadows (Marks et al. 2002).

Nonbreeding: Winter habitats are primarily throughout Polynesia in the Central and South Pacific. This species is unique among migratory shorebirds in that the entire population is confined to islands during the nonbreeding season (Marks et al. 1990). Subadults may remain in the Pacific until they are nearly three years old (Collar et al. 1992). Habitats include ocean terraces or reef flats, ocean beaches, inter-islet channels, lagoon sand beaches, lagoon coral reefs, mudflats, saltpans, coconut groves, and vegetated clearings (Pratt et al. 1987, Gill and Redmond 1992).Gill and Redmond (1992) found that wintering birds were associated principally with saltpans (36%) and inter-islet channels (27%). During molt, flightless birds take shelter during the day in dense stands of bunchgrass (Eragrostis variabilis) (Marks et al. 1990). In the Tuamotu Archipelago, curlews were found on all atolls surveyed, regardless of rat presence or absence. Most birds were detected in coastal habitats either on the ocean (44%) or lagoon shores (41%; Tibbitts et al. 2003).

Breeding territories encompass approximately 0.5-1.5 square kilometers (Gill et al. 1990) and average densities range from 0.45 birds per square kilometer in early July to 0.04 birds per square kilometer in late July (Gill and Handel 1987). Territory size varies with topography, particularly configuration of drainages, and is smaller for southern population (40-100 ha in Nulato Hills) than for northern population (150-275 ha at Neva Creek). During incubation, adults at Neva Creek regularly travel from nesting territories to communal feeding and roosting areas up to 7 km away. Adults with broods move away from nesting sites, traveling on average 0.3-1.0 km in first week, 0.5-1.6 km (up to 4.4 km) in second and third weeks, and 0.6-1.0 km (up to 2.6 km) in fourth and fifth weeks (Lanctot et al.1995).

On staging grounds, gathers in communal nocturnal roosts (in shallow water ponds) of up to approximately 120 individuals (Tibbitts 1990). The average diurnal flock size on the staging grounds is 3.1 birds (range 1-33; Handel and Dau 1988). Flock size in nonbreeding habitat ranges from a few to more than 100 individuals (Pratt et al. 1987). While on the Pacific islands, many birds lose so many primaries and secondaries during molt that they become flightless for about two weeks; during molt, birds are extremely secretive by day, hiding in dense vegetation (Marks 1993). Adults molt from July through December and juveniles throughout the year (Marks et al. 1990, Marks 1993). Estimated annual survivorship for wintering birds is 80-90% (Marks 1992). The oldest known individual was one killed on Laysan Island that had been banded 23 years, 10 months earlier (Marks 1992).

Potential predators on the breeding grounds include Golden Eagles (Aquila chrysaetos), Rough-legged Hawks (Buteo lagopus), Northern Harriers (Circus cyaneus), Merlins (Falco columbarius), Short-eared Owls (Asio flammeus), Long-tailed Jaegers, Short-tailed Weasels (Mustela erminea), red foxes, and brown bears (Ursus arctos; McCaffery 1990, Lanctot et al. 1995). On breeding grounds, known predators of adults include Gyrfalcon (Falco rusticolus); of eggs, Parasitic Jaeger (Stercorarius parasiticus) and Common Raven (Corvus corax); and of chicks, red fox (Vulpes vulpes), Northern Harrier (Circus cyaneus), Gyrfalcon (Falco rusticolis), Sandhill Crane (Grus canadensis), and Long-tailed Jaeger (McCaffery 1990, Lanctot et al. 1995, Marks et al. 2002)

Forms temporary associations with American and Pacific Golden-Plover (Pluvialis dominica and P. fulva), Whimbrel, Bar-tailed Godwit, Western Sandpiper and Long-tailed Skua (Stercorarius longicaudus). Curlews and other larger-bodied species commonly attack-mobbed predators together, whereas smaller-bodied species generally give alarm calls and circle predators (Lanctot et al.1995).

Spring migrants usually arrive singly or in groups of two, occasionally in flocks. Males often precede mates by 1-6 days. Females rarely observed before mates in same year. Nest building begins within 1-3 days of arrival. At Nulato Hills (1987-1991), most nests initiated during last two weeks of May with successful nests hatching from 15-30 June. At Neva Creek, median clutch initiation was 24-31 May, about two weeks after arrival of females. Late clutches (initiated 9-18 June) attributed to late arriving females rather than renesting attempts. Median hatching dates 22-28 June with only a few nests hatching in July. Between 95-100% of pairs hatched nests within 8-10 days in two early years and 21-22 days in one late year at Neva Creek. Second brood per season not known to occur (Marks et al. 2002).

Clutch size is typically four eggs (Kyllingstad 1948, McCaffery and Peltola 1986) which are incubated by both sexes for 24-25 days (McCaffery and Gill 1992). In the Nulato Hills of the Yukon Delta National Wildlife Refuge, 80 percent of nests beneath tundra willows hatched, whereas only about 33 percent of nests in the open were successful. Curlew nests constructed near nest sites of aggressively defensive Long-tailed Jaegers (Stercorarius longicaudus) were more successful than those in more isolated areas (McCaffery and Gill 1992). Seven of 9 nests examined by McCaffery and Peltola (1987) in the Nulato Hills were lost to predation.

Chicks are precocial and leave the nest within 12 hours of hatching. Young can fly when 21-24 days old (Lanctot et al. 1995). When 1-4 weeks old, juveniles congregate in brood aggregations (Lanctot et al. 1995). These groups typically remain intact until juveniles depart for staging areas in early August. Brood aggregations generally consist of fewer than 20 juveniles, but can contain up to 30 (McCaffery and Gill 1992, Lanctot et al. 1995). Brood groups studied by Gill et al. (1990) contained an average of 6.5 young (range = 1-12) from a minimum of 1-3 different broods. However, aggregations can include young from as many as 10 broods (Lanctot et al. 1995). Brood aggregations are tended by up to 14 parent birds, sometimes even if the aggregation does not contain any of their own young (Gill et al. 1990, McCaffery and Gill 1992, Lanctot et al. 1995). Brood aggregations move up to two kilometers per day (McCaffery and Gill 1992). Males attend aggregations 10-14 days longer than females (Gill et al. 1990). Brood aggregations often include young of other birds such as Bar-tailed Godwit (Limosa lapponica), American Golden-Plover (Pluvialis dominica), Pacific Golden-Plover (Pluvialis fulva), Whimbrel, Long-tailed Jaeger, and Western Sandpiper (Calidris mauri) (Lanctot et al. 1995). Curlews become reproductively mature in their third year (Marks 1993).