Demography and Populations

Age At First Breeding; Intervals Between Breeding

Likely does not breed until ≥3 yr old (i.e., 34–36 mo) based on direct evidence from breeding grounds and indirect evidence from wintering grounds. Female banded as a chick at Neva Creek 6 Jul 1990 and re-captured with chicks 25 Jun 1993 would have initiated breeding at about 35 mo old (TLT, REG). Marked birds <3 yr old inhabit Laysan I. year-round, with most remaining until 3 yr old and small number staying until 4 or 5 yr old (Marks and Redmond 1996 Marks, J. S. and R. L. Redmond. (1996). Demography of Bristle-thighed Curlews Numenius tahitiensis wintering on Laysan Atoll. Ibis 138:438-447. Close ). Attempts to breed annually thereafter; only 1 of 40 marked adult females and none of 50 marked adult males absent for a breeding season and then returning (TLT, REG, BJM). During 5 breeding seasons in Nulato Hills, unpaired males (sometimes same individuals) maintained territories each year (BJM), whereas individuals at Neva Creek rarely remained unpaired during breeding season (TLT, REG).

Clutch

Mean clutch size of 39 nests found 1985–2001 was 3.85 eggs ± 0.37 SD (range 3–4). Eleven complete clutches at Neva Creek contained 4 eggs each; 22 clutches in Nulato Hills contained 4 eggs each, and 6 contained 3 eggs each.

Annual And Lifetime Reproductive Success

In Nulato Hills, Mayfield estimate 37% for nesting success (n = 20 nests) and 40% for fledging success (n = 7 broods), suggesting 15% of females fledge young annually (BJM). At Neva Creek, apparent nesting success (% pairs hatching ≥1 young) estimated at 59% in 1990 (n = 27 pairs), 90% in 1991 (n = 38), and 84% in 1992 (n = 32); fledging success (% broods fledging ≥1 young) 15% in 1990 (n = 13 broods), 75% in 1991 (n = 32), and 67% in 1992 (n = 24; REG, TLT). No estimate of lifetime reproductive success.

Number Of Broods Normally Reared Per Season

One. Short breeding season and need for biparental care into middle of brood-rearing period preclude second brood.

Proportion Of Total Females That Rear At Least One Brood To Independence

No information.

Two birds banded in Northwestern Hawaiian Is. Sep 1967 resighted on Laysan I. Jul–Aug 1989 were at least 22 yr 1 mo and 22 yr 2 mo old, respectively (Marks et al. 1990 Marks, J. S., R. L. Redmond, P. Hendricks, R. B. Clapp and Jr. Gill, R. E. (1990). Notes on longevity and flightlessness in Bristle-thighed Curlews. Auk 107:779-781. Close ). Latter bird, a female, subsequently collected on Laysan I. 30 Apr 1991, at which time at least 23 yr 10 mo old (Marks 1992 Marks, J. S. (1992). Longevity record for the Bristle-thighed Curlew: an extension. Journal of Field Ornithology 63:309-310. Close ). These birds among oldest known scolopacids in North America (see Marks 1992 Marks, J. S. (1992). Longevity record for the Bristle-thighed Curlew: an extension. Journal of Field Ornithology 63:309-310. Close , Colwell et al. 1995 Colwell, M. A., R. H. Gerstenberg, O. E. Williams, and M. G. Dodd (1995). Four Marbled Godwits exceed the North American longevity record for scolopacids. Journal of Field Ornithology 2:181-183. Close , Gratto-Trevor 2000 Gratto-Trevor, C. L. (2000). Marbled Godwit (Limosa fedoa). In The Birds of North America, No. 492 (A. Poole and F. Gill, Editors). The Birds of North America, Inc., Philadelphia, Pennsylvania, USA. Close ). One adult banded at Neva Creek in 1989 and 2 banded in 1991 resighted there in 2000, making them ≥14 yr old and ≥12 yr old, respectively.

Using mark-recapture modeling, annual survivorship of adults (n = 189) wintering on Laysan I. estimated to be 85% ± 7.8 SE from 1988–1991 (Marks and Redmond 1996 Marks, J. S. and R. L. Redmond. (1996). Demography of Bristle-thighed Curlews Numenius tahitiensis wintering on Laysan Atoll. Ibis 138:438-447. Close ). Independent appraisal based on resightings on Laysan I. in 1989–1991 of 2 of 95 curlews banded in Northwestern Hawaiian Is. in 1967 yielded survival estimate of 85–90% for 1967 cohort (Marks 1992 Marks, J. S. (1992). Longevity record for the Bristle-thighed Curlew: an extension. Journal of Field Ornithology 63:309-310. Close ). Estimate of annual survivorship of adults (n = 77) breeding at Neva Creek was 87% ± 4.9 SE from 1989 to 1992, with no significant difference between sexes (TLT, REG). Once birds reach adulthood, average life expectancy (based on survival estimates) an additional 6.0 yr and 7.4 yr for birds at Laysan I. and Neva Creek, respectively. Minimum annual survival of 79 juveniles marked in calendar year of hatching on Laysan I. averaged 92% from 1988–1991 (Marks and Redmond 1996 Marks, J. S. and R. L. Redmond. (1996). Demography of Bristle-thighed Curlews Numenius tahitiensis wintering on Laysan Atoll. Ibis 138:438-447. Close ). Eighty-three percent of juveniles marked in fall 1988 still present on island at start of spring 1991; annual survivorship for cohort 92% in first year, 93% in second year, and 98% in third year, indicating extremely high survivorship on predator-free wintering islands (Marks and Redmond 1996 Marks, J. S. and R. L. Redmond. (1996). Demography of Bristle-thighed Curlews Numenius tahitiensis wintering on Laysan Atoll. Ibis 138:438-447. Close ). Survival from fledging to arrival on wintering grounds unknown.

Diseases

No information.

Body Parasites

Three species of lice (order Phthiraptera) recorded: Austromenopon phaeopodis (family Menoponidae) from just south of Johnston Atoll; Lunaceps numenii hopkinsi (family Philopteridae) from Kure Atoll, Midway Atoll, and Vostok I.; and Saemundssonia scolopacisphaeopodis (family Philopteridae) from Midway Atoll (Amerson and Emerson 1971 Amerson, A. B., Jr., and K. C. Emerson (1971). Records of Mallophaga from Pacific birds. Atoll Research Bulletin 146:1–30. Close ).

Exposure

No information. Presumably a factor on breeding grounds, where chicks vulnerable to hypothermia if unattended during inclement weather. During severe wind storms on Laysan I., curlews sought shelter in dense cover, but no mortality noted (JSM).

Predation

See Behavior: Predation, above. In absence of human influences, predation unlikely to be major source of mortality affecting population trends. Common Raven numbers appear artificially high on breeding grounds in Nulato Hills, perhaps because birds receive supplemental food at garbage dumps in nearby villages; raven predation of curlew eggs and chicks may decrease reproductive success; needs study (BJM).

Historically, wintering grounds largely predator-free, although curlews could be taken by Peregrine Falcons (Falco peregrinus) that occur sporadically on remote islands (JSM). Introduced mammals (e.g., dogs, cats, pigs [Sus scrofa], rats [Rattus spp.]) likely to be important predators of wintering curlews during molt-induced flightless period (Marks et al. 1990 Marks, J. S., R. L. Redmond, P. Hendricks, R. B. Clapp and Jr. Gill, R. E. (1990). Notes on longevity and flightlessness in Bristle-thighed Curlews. Auk 107:779-781. Close , Gill and Redmond 1992 Gill, Jr., R. E. and R. L. Redmond. (1992). Distribution, numbers, and habitat of Bristle-thighed Curlews (Numenius tahitiensis) on Rangiroa Atoll. Notornis 39:17-26. Close ), but no data.

Competition With Other Species

Unlikely to lead to mortality, but no information.

Initial Dispersal From Natal Site

Two of 102 unsexed chicks banded at Neva Creek resighted in later years. First was 36-mo-old female that nested successfully <2 km from natal site (TLT, REG; see Measures of breeding activity, above). Second was male seen ≥8 yr after banding but not identifiable as individual nor confirmed as breeder.

Fidelity To Breeding Site And Winter Home Range

Adults highly faithful to breeding sites. At Neva Creek, 81% of color-banded males (n = 43) and 82% of color-banded females (n = 34) returned in year(s) subsequent to banding (TLT, REG); at Curlew Lake, 100% of males (n = 8) and 63% of females (n = 8) returned (BJM). At both sites, almost all males bred within approximate boundaries of previous breeding territories; exception from Nulato Hills seen only briefly in early May of year after banding and not seen again (BJM). Females with new males (n = 6) bred up to 7.5 km from territory of previous year (TLT, REG, BJM). Site fidelity also high on wintering grounds. From 1988 to 1991, 80% of adults returned to Laysan I. in year after marking, many occupying same place on island for multiple years (Marks and Redmond 1996 Marks, J. S. and R. L. Redmond. (1996). Demography of Bristle-thighed Curlews Numenius tahitiensis wintering on Laysan Atoll. Ibis 138:438-447. Close ). At least 60% of surviving subadults marked from 1988 to 1990 returned to Laysan I. to winter as adults (Marks and Redmond 1996 Marks, J. S. and R. L. Redmond. (1996). Demography of Bristle-thighed Curlews Numenius tahitiensis wintering on Laysan Atoll. Ibis 138:438-447. Close ).

Dispersal From Breeding Site

Little information. Female radio-tagged at nest failed to return to site in following spring but observed in Russia 500 km away, perhaps having been blown off course during migration (Konyukhov and McCaffery 1993 Konyukhov, N. B. and B. J. McCaffery. (1993). Second record of a Bristle-thighed Curlew from Asia and first record for the former Soviet Union. Wader Study Group Bulletin 70:22-23. Close ; see Distribution and Habitat: Distribution Outside the Americas, above). Not known whether she died or bred elsewhere.

Home Range

Territory size varies with topography, particularly configuration of drainages, and is smaller for southern population (40–110 ha in Nulato Hills; BJM) than for northern population (150–275 ha at Neva Creek; REG, TLT). During incubation, adults at Neva Creek regularly travel from nesting territories to communal feeding and roosting areas up to 7 km away (TLT, REG). 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 Lanctot, R. B., Jr. Gill, R. E., T. L. Tibbitts, and C. M. Handel (1995). Brood amalgamation in the Bristle-thighed Curlew Numenius tahitiensis: process and function. Ibis 137:559–569. Close ).

Numbers

Comprehensive surveys of known breeding range 1988–1992 yielded about 3,200 breeding pairs, 60% in Nulato Hills and 40% on Seward Peninsula (C. Handel unpubl.). Breeding densities higher at Curlew Lake (0.67–0.80 pairs/km², n = 4 yr) and Allen Creek (2.6 territorial males/km², n = 1 yr) study areas in Nulato Hills (BJM) than at Neva Creek (0.28–0.36 pairs/km², n = 3 yr) study area on Seward Peninsula (REG, TLT).

Best winter population information from mark-recapture study on Laysan I. 1988–1990, during which 330, 395, and 288 birds, respectively, estimated on island (Marks and Redmond 1996 Marks, J. S. and R. L. Redmond. (1996). Demography of Bristle-thighed Curlews Numenius tahitiensis wintering on Laysan Atoll. Ibis 138:438-447. Close ). In total, about 800 birds thought to winter in Northwestern Hawaiian Is. during same period: 300–350 on Laysan I., 300–400 on Lisianski I., and 100 on Midway Atoll (Marks and Redmond 1994a Marks, J. S. and R. L. Redmond. (1994a). Conservation problems and research needs for Bristle-thighed Curlews Numenius tahitiensis on their wintering grounds. Bird Conservation International 4:329-341. Close ). Other estimates of large numbers on wintering grounds include >200 on Palmyra Atoll, Line Is. (R. Redmond pers. comm.); 300 on Caroline Atoll, Line Is. (extrapolation from 83 birds counted on line transects; Kepler et al. 1994 Kepler, C. B., A. K. Kepler and D. H. Ellis. (1994). The natural history of Caroline Atoll, southern Line Islands. Part 2. Seabirds, other terrestrial animals, and conservation. Atoll Research Bulletin 398:1-61. Close ); 200 each on Palmerston Atoll and Takutea I., Cook Is. (Burland 1964 Burland, J. C. (1964). Some notes on the bird life of Palmerston Atoll. Notornis 11:145-154. Close , Holyoak 1976 Holyoak, D. T. (1976). Records of waders in the Cook Islands. Notornis 23:1-3. Close , Mccormack 1991 Mccormack, G. (1991). Takutea: a wildlife report from 1986 to 1990. Rarotonga, Cook Islands: Prime Minister's Dep. Close ); 250–350 on Rangiroa Atoll, Tuamotu Archipelago (Gill and Redmond 1992 Gill, Jr., R. E. and R. L. Redmond. (1992). Distribution, numbers, and habitat of Bristle-thighed Curlews (Numenius tahitiensis) on Rangiroa Atoll. Notornis 39:17-26. Close ); and 100 on Oeno I., Pitcairn Is. (Brooke 1995 Brooke, M. de L. (1995). The modern avifauna of the Pitcairn Islands. Biological Journal of the Linnean Society 56:199-212. Close ). Smaller numbers reported from numerous locations on wintering grounds (e.g., Thompson and Hackman 1968 Thompson, M. C. and C. D. Hackman. (1968). Birds of the Tokelau Islands. Notornis 15:109-117. Close , Amerson 1969 Amerson, Jr., A. B. (1969). Ornithology of the Marshall and Gilbert islands. Atoll Research Bulletin 127. Close , Clapp 1977 Clapp, R. B. (1977). Notes on the vertebrate fauna of Tongareva Atoll. Atoll Research Bulletin 198. Close , Holyoak 1980 Holyoak, D. T. (1980). Guide to Cook Islands birds. Wellington, New Zealand: Cook Islands Library and Mus. Soc. Close , Smart 1981 Smart, J. B. (1981). Notes on the occurrence of waders in Fiji. Notornis 28:267-279. Close , Holyoak and Thibault 1984 Holyoak, D. T., and J.-C. Thibault. (1984). Contribution à l’étude des oiseaux de Polynésie orientale. Mémoires du Muséum national d’histoire naturelle Serie A, Zoologie 127:1–209. Close , Gill 1995a Gill, B. J. (1995a). Notes on the birds of Wallis and Futuna, south-west Pacific. Notornis 42:17-22. Close , Buden 1996 Buden, D. W. (1996). Reptiles, birds, and mammals of Pakin Atoll, eastern Caroline Islands. Micronesica 29:37-48. Close , Blanvillain et al. 2002 Blanvillain, C., C. Florent and V. Thenot. (2002). 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). Biological Conservation 103:139-149. Close ).

Reports of 1,000 Bristle-thighed Curlews on Laysan I. Apr 1915 and Sep 1918 (Munter 1915 Munter, W. H. (1915). Report of destruction of bird life on Laysan Island. Annu. Rep., Coast Guard for 1915:130-140. Close , Ely and Clapp 1973 Ely, C. A. and R. B. Clapp. (1973). The natural history of Laysan Island Northwestern Hawaiian Islands. Atoll Research Bulletin 171. Close ) almost surely overestimates (JSM, R. Clapp pers. comm.). Counts made by nonbiologists visiting island when curlews in flocks associated with migration and when most vegetation removed by European rabbits. Thus, curlews would be aggregated and readily visible but easily overcounted as flocks flushed multiple times.

Trends

Needs study. Systematic counts by U.S. Fish and Wildl. Serv. at Tern I. in Northwestern Hawaiian Is. (D. O'Daniel unpubl.) provide only long-term trend data from wintering grounds. Average number of birds present throughout winter declined steadily from 11.8 in 1988 to 0.6 in 2000 (R 2 = 0.72, P < 0.001; data log transformed). Tern I. not major wintering site for curlews (Amerson 1971 Amerson, A. B. (1971). The natural history of French Frigate Shoals, Northwestern Hawaiian Islands. Atoll Research Bulletin 150:1-383. Close , JSM), however, so data may not be indicative of population trends elsewhere on wintering grounds.

Needs study. Given high survival of all age classes on Northwestern Hawaiian Is. (see Lifespan and survivorship, above), events on winter range probably had little influence on population regulation before arrival of humans. Increased mortality in winter owing to human encroachment and predation by exotic mammals likely important in current population regulation. Not known whether current nesting success adequate to maintain population stability.