Bristle-thighed Curlews Research Articles

Population trends, size, and potential threats to Bristle-thighed Curlew Numenius tahitiensis: new data from French Polynesia

Summary Based on censuses in 2021 and 2022 of Bristle-thighed Curlews Numenius tahitiensis on 10 atolls of French Polynesia, the species has declined by c.50% over the last two decades. While the species has recently been down-listed from “Vulnerable” to “Near Threatened”, these new data would qualify it for an “Endangered” Red List status. The non-breeding population on Tuamotu numbers approximately 1,000 curlews and up to 1,500 individuals in all of Eastern Polynesia. On uninhabited islands, the expansion of copra (coconut pulp) exploitation has caused long-term disturbance for curlews, increased predation by pet dogs, and introduced or reinforced non-native rat populations. Climate change, particularly sea-level rise, will add to changes in land use that shrink the suitable habitat for Bristle-thighed Curlews in French Polynesia. As this study shows, obtaining population trends for species breeding in remote areas may best be achieved through surveys at key non-breeding sites.

The 46th Annual Report of the California Bird Records Committee: 2020 Records

From its last report through 2020, the California Bird Records Committee reached decisions on 206 records involving 195 individuals of 67 species and two species groups, endorsing 180 records of 169 individuals. Especially notable records detailed in this report include those of California’s third Common Crane (Grus grus), third Bristle-thighed Curlew (Numenius tahitiensis), third Marsh Sandpiper (Tringa stagnatalis), third Eurasian Skylark (Alauda arvensis), fourth Chuck-will’s-widow (Antrostomus carolinensis), and fourth Fork-tailed Flycatcher (Tyrannus savanna).

Through thick and thin: Sexing Bristle-thighed Curlews Numenius tahitiensis using measures of bill depth

Through thick and thin: Sexing Bristle-thighed Curlews Numenius tahitiensis using measures of bill depth

Factors promoting the recolonization of Oahu, Hawaii, by Bristle-thighed Curlews

Suitable habitat for Arctic-breeding migratory shorebirds is decreasing at their traditional wintering islands and atolls in the Central Pacific Flyway (i.e., Oceania) due to habitat degradation, reclamation, and sea-level rise. To maintain the size and resiliency of their populations, migratory shorebirds will need to expand their winter ranges by either colonizing new sites or recolonizing old sites from which they were extirpated. Bristle-thighed Curlews (Numenius tahitiensis) are long-distance migratory shorebirds that breed only in Alaska and winter across a vast region of the Central Pacific, typically on remote, unpopulated islands and atolls. Historically, Bristle-thighed Curlews were considered uncommon transients on the main Hawaiian Islands, but in the mid-1990s, curlews became regular visitors to Oahu and subsequently began wintering at the James Campbell National Wildlife Refuge on Oahu Island in Hawaii. Curlew numbers at this site grew steadily from <5 birds in the mid-1990s to an estimated 126 winter residents (95%CI 108–147) in 2013–2014. Timing of the recolonization event coincided with the establishment of a fenced pond complex that was managed for endangered waterbirds by maintaining areas of shallow water and low vegetation. High rates of apparent annual survival exhibited by adults and subadults (0.86–0.95) confirmed the suitability of the Refuge to curlews. Our results suggest that curlews in Oceania can naturally recolonize wintering islands, a trait that may be key to the survival of this species of conservation concern in an era of rising sea levels.

Survival of Bristle-thighed Curlews equipped with externally mounted transmitters

Survival of Bristle-thighed Curlews equipped with externally mounted transmitters

Habitat Selection By Bristle-Thighed Curlews (Numenius tahitiensis) Breeding Within The Southern Nulato Hills, Alaska

ABSTRACT Bristle-thighed Curlews (Numenius tahitiensis, hereafter ‘curlews') breed only on low Arctic tundra in the southern Nulato Hills of the Yukon Delta National Wildlife Refuge (NWR) and on the Seward Peninsula, Alaska. Curlews use several distinct habitat types on the breeding grounds; however, quantified data of habitat use by curlews exist only for the Seward Peninsula. We investigated which available habitats on the breeding grounds were used most often by curlews in the Nulato Hills and compared availability with use to determine habitat selection using a land cover layer created in ArcGIS based on aerial photography and ground referenced locations. We also compared curlew habitat usage at our study site to habitats used on the Seward Peninsula. We used vegetation quadrats to determine plant composition within each habitat. We also determined percentage of habitat and plant composition within curlew territories. Curlews preferred shrub meadow tundra which consisted primarily of lichens (>50%), m...

Ecology of a Vulnerable Shorebird across a Gradient of Habitat Alteration: Bristle-Thighed Curlews (Numenius tahitiensis) (Aves: Charadriiformes) on Palmyra Atoll1

Abstract: Palmyra Atoll, USA, in the Central Pacific, has remained mostly uninhabited since construction and abandonment of a U.S. naval base during World War II. However, the effects of Navy modifications have persisted, affecting physical conditions and benthic habitat quality of Palmyra's lagoon sand flats. Sand flats provide important nonbreeding habitat for Bristle-thighed Curlews (Numenius tahitiensis), a migratory shorebird listed as “vulnerable” by the International Union for Conservation of Nature and Natural Resources. We used camera trapping, observations of focal individuals, and quantification of prey availability and sediment characteristics to assess curlew habitat use across different levels of historical anthropogenic impact. Habitat preferences were not determined by the degree of land reclamation impact on lagoon flat habitat, although the two most preferred sites were both highly impacted. Curlew abundance was most strongly correlated with availability of prey items, such as spionid po...

The Avifauna of Kosrae, Micronesia: History, Status, and Taxonomy

Abstract: Kosrae, the easternmost high island of Micronesia, is a 110 km2 volcanic island rising up to 630 m above sea level. It is seldom visited by birders and ornithologists because it is small, isolated, and lacks any previously recognized extant endemic bird species. We review the history of research on the island's avifauna and summarize the status of each species, including documentation for six new species: Northern Pintail (Anas acuta), Gray Plover (Pluvialis squatarola), Common Snipe (Gallinago gallinago), Bristle-thighed Curlew (Numenius tahitiensis), Red-necked Stint (Calidris ruficollis), and Whiskered Tern (Chlidonias hybrida). We discuss previously undescribed vocalizations of endemic taxa and provide online reference to recordings. We also present supporting evidence for the recognition of two taxa as full biological species: Kosrae Fruit Dove (Ptilinopus hernsheimi; formerly part of the P. porphyraceus complex) and Kosrae White-eye (Zosterops cinereus, as a split from Gray-brown White-eye...

35. ‘Slamming’ behaviour by foraging Bristle-thighed Curlews

35. ‘Slamming’ behaviour by foraging Bristle-thighed Curlews

Spatial genetic structure of bristle-thighed curlews (Numenius tahitiensis): breeding area differentiation not reflected on the non-breeding grounds

Migratory birds occupy geographically and ecologically disparate areas during their annual cycle with conditions on breeding and non-breeding grounds playing separate and important roles in population dynamics. We used data from nuclear microsatellite and mitochondrial DNA control region loci to assess the breeding and non-breeding spatial genetic structure of a transoceanic migrant shorebird, the bristle-thighed curlew. We found spatial variance in the distribution of allelic and haplotypic frequencies between the curlew’s two breeding areas in Alaska but did not observe this spatial structure throughout its non-breeding range on low-lying tropical and subtropical islands in the Central Pacific (Oceania). This suggests that the two breeding populations do not spatially segregate during the non-breeding season. Lack of migratory connectivity is likely attributable to the species’ behavior, as bristle-thighed curlews exhibit differential timing of migration and some individuals move among islands during non-breeding months. Given the detrimental impact of many past and current human activities on island ecosystems, admixture of breeding populations in Oceania may render the bristle-thighed curlew less vulnerable to perturbations there, as neither breeding population will be disproportionally affected by local habitat losses or by stochastic events. Furthermore, lack of migratory connectivity may enable bristle-thighed curlews to respond to changing island ecosystems by altering their non-breeding distribution. However, availability of suitable non-breeding habitat for curlews in Oceania is increasingly limited on both low-lying and high islands by habitat loss, sea level rise, and invasive mammalian predators that pose a threat to flightless and flight-compromised curlews during the molting period.

Polymorphic microsatellite loci identified through development and cross-species amplification within shorebirds

We developed microsatellite loci for demographic assessments of shorebirds, a group with limited markers. First, we isolated five dinucleotide repeat microsatellite loci from the Black Oystercatcher (Haematopodidae: Haematopus bachmani), and three from the Bristle-thighed Curlew (Scolopacidae: Numenius tahitiensis); both species are of conservation concern. All eight loci were polymorphic in their respective target species. Hbaμ loci were characterized by two to three alleles with observed heterozygosity ranging from 0.07 to 0.33, and two to nine alleles were detected for Nut loci with observed heterozygosity ranging from 0.08 to 0.72. No linkage disequilibrium or departures from Hardy–Weinberg equilibrium were observed. The eight loci were also tested for cross-species amplification in 12 other species within Charadriidae and Scolopacidae, and the results demonstrated transferability across several genera. We further tested all 14 species at 12 additional microsatellite markers developed for other shorebirds: Dunlin (Calidris alpina; four loci) and Ruff (Philomachus pugnax; eight loci). Two markers (Hbaμ4 and Ruff6) were polymorphic in 13 species, while two (Calp6 and Ruff9) were monomorphic. The remaining eight markers revealed polymorphism in one to nine species each. Our results provide further evidence that locus Ruff10 is sex-linked, contrary to the initial description. These markers can be used to enhance our understanding of shorebird biology by, for example, helping to determine migratory connectivity among breeding and wintering populations and detecting relatedness among individuals.

Coelomic Implantation of Satellite Transmitters in the Bar-tailed Godwit (Limosa lapponica) and the Bristle-thighed Curlew (Numenius tahitiensis) Using Propofol, Bupivacaine, and Lidocaine

Intravenous propofol was used as a general anesthetic with a 2:1 (mg:mg) adjunctive mixture of lidocaine and bupivacaine as local anesthetics infiltrated into the surgical sites for implantation of satellite transmitters into the right abdominal air sac of 39 female and 4 male bar-tailed godwits (Limosa lapponica baueri and Limosa lapponica menzbeiri and 11 female and 12 male bristle-thighed curlews (Numenius tahitiensis). The birds were captured on nesting grounds in Alaska, USA, and on overwintering areas in New Zealand and Australia from 2005 through 2008. As it was developed, the mass of the transmitter used changed yearly from a low of 22.4 +/- 0.2 g to a high of 27.1 +/- 0.2 g and weighed 25.1 +/- 0.2 g in the final year. The mean load ratios ranged from 5.2% to 7.7% for godwits and from 5.7% to 7.5% for curlews and exceeded 5% for all years, locations, and genders of both species. The maximum load ratio was 8.3% for a female bar-tailed godwit implanted in Australia in 2008. Three godwits and no curlews died during surgery. Most birds were hyperthermic upon induction but improved during surgery. Two godwits (one in New Zealand and one in Australia) could not stand upon release, likely due to capture myopathy. These birds failed to respond to treatment and were euthanized. The implanted transmitters were used to follow godwits through their southern and northern migrations, and curlews were followed on their southern migration.

Land birds of Tuamotu Archipelago, Polynesia: relative abundance and changes during the 20th century with particular reference to the critically endangered Polynesian ground-dove ( Gallicolumba erythroptera)

We report relative abundances and distributions of land bird communities on eight isolated islands of the Tuamotu Archipelago (Polynesia, South Pacific Ocean) during two 21-day expeditions in 1999. The selection of islands was based on the historical range of the Polynesian ground-dove ( Gallicolumba erythroptera), in the hope of finding populations of this critically endangered species. Data were also collected on the Tuamotu sandpiper Prosobonia cancellata, the Atoll Fruit-dove Ptilinopus coralensis, the Tuamotu reed-warbler Acrocephalus atyphus, the Spotless Crake Porzana tabuensis and the Bristle-thighed Curlew Numenius tahitiensis, and on introduced predators (cats, rats, pigs and dogs). None of the five land-bird species recorded previously, in 1922 and 1974, has completely disappeared, but ranges of several species have contracted. Only one population of G. erythroptera erythroptera was found and it is the only population known for this species today. Our data also raise particular concern for the future of the Tuamotu sandpiper.

The status of seabird colonies on the Cook Islands atoll of Suwarrow

Suwarrow (Suvorov) atoll is an important seabird breeding site in the central Pacific Ocean. However, it is not protected and is attractive to developers of potentially damaging aquaculture industries. In this paper I report the results of a survey conducted to establish the present status of Suwarrow's seabird colonies and to generate base-line data for measuring the effect of a proposed pearl-farm development. Between late July and early September 2000 the reef islets were surveyed for seabird chick numbers and age-states using a simple sampling method. In addition to Sooty Tern Sterna fuscata, populations of boobies Sula spp., noddies Anous spp., frigatebirds Fregata spp. and tropicbirds Phaethon spp. were assessed. Results showed that bird populations were maintaining levels similar to those from findings of surveys in 1992. Of particular note were globally significant numbers of Lesser Frigatebird Fregata ariel and Red-tailed Tropicbird Phaethon rubricauda. Migratory birds were observed with Bristle-thighed Curlew Numenius tahitiensis regularly seen. The well-being of bird-life on the islets appears to be indirectly proportional to the proximity of human activity, with birds not observed breeding on Anchorage Island – the islet most often visited by people.

Phenotypic Flexibility during Migration: Optimization of Organ Size Contingent on the Risks and Rewards of Fueling and Flight?

Avian long-distance migration involves the storage and expenditure of very large fuel loads. Birds may double in weight before take-off on flights of many 1000 km, and they may lose half their body mass over the subsequent few days that such trips take. Recent studies indicate that in addition to the storage and depletion of fat, the muscles and belly organs also undergo considerable changes in size in the course of such migrations. Such intraindividual and repeatedly reversed changes in stores and organ sizes represent a class of phenotypic plasticity called 'phenotypic flexibility'. Using preliminary comparative data for different populations of Bar-tailed Godwits Limosa lapponica, and several other shorebird species adding variation to the migration strategies sampled (Golden Plover Pluvialis apricaria, Ruff Philomachus pugnax, Red Knot Calidris canutus and Bristle-thighed Curlew Numenius tahitiensis), the thesis is developed that the size of the organs carried during take-off represent evolutionary compromises between their functions during the storage, flight and post-arrival phases of migration. In all cases fat-free tissue along with fat is deposited during fuel storage, but the proportions vary a great deal between similarly sized species. Just before departure on long-distance flights, exercise organs (pectoral muscle and heart) tend to show hypertrophy and nutritional organs (stomach, intestine and liver) tend to show atrophy. Reductions in nutritional organs appear most pronounced in (sub-) species that are about to overfly barren oceans with few or no opportunities for emergency landings. Migrant birds seem to show a great deal of adaptive flexibility, and the study of this flexibility may shed light on (presently unknown) physiological mechanisms as well as on correlated ecological constraints on bird migration.

Demography of Bristle‐thighed Curlews Numenius tahitiensis wintering on Laysan Island

We studied the nonbreeding ecology of Bristle‐thighed Curlews Numenius tahitiensis from 1988 to 1991 on Laysan Island in the Northwestern Hawaiian Islands. Using capture‐recapture analysis, we estimated that 300–350 curlews wintered on the island. Annual survival was &gt;85% for adults and 92% for first‐year birds. Young birds remained on the island until at least their third calendar year, when some individuals made “exploratory” visits to other islands in the Northwestern chain. Most of the birds marked in their first year migrated north to the breeding grounds when they were 3 years old; several birds remained on the island until they were at least 4 years old. Adults returned to the same discrete home ranges year after year, whereas subadults (which do not migrate) tended to use a greater portion of the island. At least 60% of the subadults marked from 1988 to 1990 returned to the island to winter as adults. Because young curlews arrived after adults and experienced high survivorship while on the island, there did not appear to be intense competition for space at Laysan even though the island is at the northern end of the species' winter range.

Brood amalgamation in the Bristle‐thighed Curlew Numenius tahitiensis: process and function

Alloparental care in birds generally involves nonbreeding adults that help at nests or breeding adults that help raise young in communal nests. A less often reported form involves the amalgamation of broods, where one or more adults care for young that are not their own. We observed this phenomenon among Bristle‐thighed Curlew Numenius tahitiensis broods in western Alaska during 1990–1992. Amalgamation of broods generally involved the formation of temporary and extended associations. Temporary associations were formed by the incidental convergence of broods soon after they left their nests. During this period, parents defended distinct brood‐rearing areas, were antagonistic to conspecifics and remained together for less than 3 days. Extended associations formed when chicks were 1–2 weeks old. Here, parents and their broods occupied distinct, but adjacent, brood‐rearing areas and moved around as a unit. Whether a brood participated in either temporary or extended associations or remained solitary appeared to depend on brood density in the immediate area and on hatching date. When chicks were 3–4 weeks old, aggregations of up to ten broods formed wherein young mixed and parents defended a common brood‐rearing area. All broods (n = 48) that survived to fledging joined such aggregations. Alloparental care involved only antipredator defence and was not associated with activities such as feeding and brooding. Most female parents abandoned their broods shortly after the young could fly and when aggregations were forming. The female parent of a pair always deserted its young before or on the same day as the male parent and, in every aggregation, one or two males continued to tend young for about 5 days longer than other male parents. In most cases, adults deserted the young 2–6 days before the young departed the area when about 38 days old. Bristle‐thighed Curlews also formed temporary associations with American and Pacific Golden Plover Pluvialis dominica and Pluvialis fulva, Whimbrel Numenius phaeopus, Bar‐tailed Godwit Limosa lapponica, Western Sandpiper Cal‐idris mauri and Long‐tailed Skua Stercorarius longicaudus. Curlews and other larger bodied species commonly attack‐mobbed predators together, whereas smaller bodied species generally gave alarm calls and circled the predators. For all species, the intensity of antipredator defence by attending adults gradually decreased as young became older and aggregations formed. We suggest that amalgamation of broods among Bristle‐thighed Curlew enhances predator defence, aids in the process of flock formation for migrating young, and allows females and some males to desert their young earlier.

The modern avifauna of the Pitcairn Islands

Abstract Excluding the gadfly petrelsPterodromaspp. and the resident landbirds, this paper details the present status of bird species seen during an expedition to the Pitcairn Islands (Ducie, Henderson, Oeno and Pitcairn) in 1991 and early 1992. Ten species were recorded in the Islands for the first time. Several Southern Ocean petrels were recorded, most in the midwinter period of June and July. The populations of Christmas Island shearwaters breeding on Oeno and Ducie laid in synchrony every 9–10 months. The species is one of few with such a sub-annual, synchronized regime. The majority of other seabirds had an annual breeding cycle, laying between May and October. Around one percent of the world population of the bristle-thighed curlew passes the non-breeding season in the Pitcairn Islands.

Conservation problems and research needs for Bristle-thighed Curlews Numenius tahitiensis on their wintering grounds

SummaryThe Bristle-thighed Curlew Numenius tahitiensis is a rare shorebird that breeds in western Alaska and winters on oceanic islands in the tropical and subtropical Pacific Ocean. Before human colonization, the islands on which curlews winter were devoid of terrestrial predators, allowing curlews to evolve a rapid moult during which about 50% of adults become flightless. Especially when flightless, these birds are vulnerable to harvest by humans and to predation by introduced mammals such as dogs and cats. On atolls where they are harvested by humans, curlews tend to occur only on uninhabited islets. Consequently, human encroachment in Oceania has probably reduced Bristle-thighed Curlew numbers and altered winter distribution of the species. Future studies should (1) identify concentrations of wintering curlews, focusing in the Tuamotu Archipelago; (2) determine whether migratory stopover sites exist in the central Pacific between Hawaii and the southern end of the wintering grounds; and (3) establish a monitoring programme to assess population trends in several parts of the winter range. A comprehensive plan is needed to provide for the existence of predator-free islands throughout key portions of the winter range.

Migration of Bristle-Thighed Curlews on Laysan Island: Timing, Behavior and Estimated Flight Range

Bristle-thighed Curlews (Numenius tahitiensis) fly at least 4,000 km non-stop from staging grounds in western Alaska to the northern edge of the winter range at Laysan Island in the Northwestern Hawaiian Islands. Adults migrate from Laysan in early May and return in July and August. Juveniles, which arrive in late August and early September, largely migrate unaccompanied by adults. Compared with other shorebirds, Bristle-thighed Curlews migrate in small flocks and show no diurnal pattern in timing of departures. Subadults do not fatten adequately for migration but often accompany departing adults briefly and then return to the island. Fat content in adults at the start of spring migration is high, averaging 42%. Our findings indicate that curlews wintering in the Central and South Pacific overfly Hawaii during spring and autumn, undertaking non-stop flights of >6,000 km. In the absence of tailwinds, only two of the four flight range models that we tested (Summers and Waltner 1979, Davidson 1984) provide reasonable estimates of the migratory performance of Bristle-thighed Curlews (i.e., non-stop flights from Alaska to Laysan and beyond). Within the range of altitudes at which they migrate, curlews probably seek out tailwinds that facilitate long-distance, non-stop flights.