Movements and Migration

Long-distance transoceanic migrant between breeding grounds in w. Alaska and wintering grounds in central and s. Oceania. Birds migrating between southernmost wintering islands and Alaska (>8,500 km) possibly use stopover sites in Central Pacific (Marks and Redmond 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 , Marks and Redmond 1994b Marks, J. S. and R. L. Redmond. (1994b). Migration of Bristle-thighed Curlews on Laysan Island: timing, behavior and estimated flight range. Condor 96:316-330. Close ). Few coastal spring records in Alaska indicate direct flight most years to breeding grounds (Gill and Handel 1981a Gill, Jr., R. E. and C. M. Handel. (1981a). "Shorebirds of the eastern Bering Sea." In The eastern Bering Sea shelf: oceanography and resources, edited by D. W. Hood and J. A. Calder, 719-738. Seattle: Univ. of Washington Press. Close ). Young birds typically remain on wintering grounds until 3–4 yr old before making first northward migration (Marks and Redmond 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 ).

Follows Central Pacific Flyway. Exact routes unknown. Migration largely oceanic, presumably in direct line between wintering islands and breeding grounds, with birds seldom landing in Americas outside of Alaska (but see below).

From 1988 to 2002, 7 birds color-banded on southern breeding grounds in Nulato Hills seen in Northwestern Hawaiian Is. (JSM, S. Bailey, B. Casler, and J. Gilardi pers. comm.). Similarly, 7 birds color-banded in Northwestern Hawaiian Is. seen in Nulato Hills (BJM). Four individuals marked in Alaska seen in winter 1992 at Palmyra Atoll, 2,000 km south of Hawaiian Is. (E. Flint pers. comm.); 2 were from Neva Creek on Seward Peninsula, but breeding origin of other 2 not determined. Thus, birds that winter in Northwestern Hawaiian Is. seem to come from southern breeding population in Nulato Hills, and those that breed on Seward Peninsula apparently winter south of Hawaiian Is., suggesting leapfrog migration. Birds from the 2 breeding populations must overlap in distribution somewhere in Central Pacific, but data lacking. Some movement among Hawaiian Is., especially during southward migration by adults and by nonbreeding 2-yr-olds in late summer (see below), but such movements poorly understood.

Spring

Peak in numbers Apr–May on Christmas I. (Gallagher 1960 Gallagher, M. D. (1960). Bird notes from Christmas Island, Pacific Ocean. Ibis 102 (4):489-502. Close ) and at several sites in Northwestern Hawaiian Is. (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 , Amerson et al. 1974 Amerson, A. B., Jr, R. C. Clapp and III W. O. Wirtz. (1974). The natural history of Pearl and Hermes Reef, Northwestern Hawaiian Islands. Atoll Research Bulletin 174. Close , Clapp and Wirtz Clapp and Wirtz II 1975 Clapp, R. B., and W. O. Wirtz II (1975). The natural history of Lisianski Island, northwestern Hawaiian Islands. Atoll Research Bulletin 186. Close ), but birds unmarked. Northward departure of marked birds monitored closely at Laysan I. in 1991 (Marks and Redmond 1994b Marks, J. S. and R. L. Redmond. (1994b). Migration of Bristle-thighed Curlews on Laysan Island: timing, behavior and estimated flight range. Condor 96:316-330. Close ). The 16 observed departures occurred 1–13 May, with most (75% of departures, 91% of individuals) occurring 1–9 May. Observations at French Frigate Shoals, Laysan I., and Midway Atoll in other years also support notion that departure from Northwestern Hawaiian Is. typically occurs during first 2 wk of May (JSM).

Most northbound migrants overfly Aleutian Is. to arrive at breeding areas in first 3 wk of May. At Mountain Village, AK, at southern end of breeding range, first birds seen 9–18 May from 1944 to 1947 (Kyllingstad 1987 Kyllingstad, H. C. (1987). In search of an Alaskan curlew. Birder's World 1 (3):22-26. Close ). More recently, first arrivals 3–6 May 1988–1991 in Nulato Hills 32 km north of Mountain Village and 8–18 May 1990–1992 at Neva Creek, suggesting earlier arrival for southern population. First spring birds in Nulato Hills probably passage migrants rather than local breeders. Over 3 yr at 1 site, first returning marked breeders arrived average of 4 d after species first detected (range 0–8 d; BJM). Arrival of returning breeders highly synchronous. Last returning breeders arrived average of 9 d after species first detected (range 5–16 d), but only 5 d (range 2–8) after first known breeders (BJM). At Neva Creek, all resident breeders present 12–14 d after first arrival (REG, TLT). Records elsewhere in w. Alaska generally consistent with arrival dates on breeding grounds, but nowhere reported in large enough numbers to suggest regular stopover; e.g., casual (1–4 individuals/sighting) mid- to late May on Aleutian Is., including Attu I., Amchitka I., Shemya I., Buldir I., and Adak I. (Gibson 1981 Gibson, D. D. (1981). Migrant birds at Shemya Island, Aleutian Islands, Alaska. Condor 83:65–77. Close , Byrd and Day 1986 Byrd, G. V. and R. H. Day. (1986). The avifauna of Buldir Island, Aleutian Islands, Alaska. Arctic 39 (2):109-118. Close , Tobish and Isleib 1992a Tobish, Jr., T. G. and M. E. Isleib. (1992a). Alaska Region. American Birds 46:462-465. Close , UAM unpubl.); small numbers almost every year on Pribilof Is. in mid-May (UAM unpubl.), earliest 5 May 2001 (P. Tomkovich pers. comm.); a few records 9–18 May from Izembek Lagoon on north side of Alaska Peninsula (UAM unpubl., TLT). Recorded Yukon Delta most years, but numbers irregular (mean arrival 14 May ± 7 d SD [range 3–21 May 1985–1996]; C. Ely unpubl.).

North of Yukon Delta, recorded at St. Michael, 24 May 1880 (Nelson 1887a Nelson, E. W. (1887). Birds of Alaska with a partial bibliography of Alaska ornithology. In Report upon Natural History Collections Made in Alaska Between the Years 1877 and 1881 (H. W. Henshaw, Editor). Signal Service, U.S. Army, Arctic Series Publication 3. U.S. Government Printing Office, Washington, DC, USA. pp. 19–226. Close ), at Golovin, 13 May 1981 (Kessel 1989 Kessel, B. (1989). Birds of the Seward Peninsula, Alaska: Their Biogeography, Seasonality and Natural History. University of Alaska Press, Fairbanks, AK, USA. Close ), and in Nome area, 23 May 1905 and 28 May 1922 (Bent 1929 Bent, A. C. (1929). Life histories of North American shorebirds, Part 2. United States National Museum Bulletin 146. Close ). Interesting “shortstop” by migrants in 1992 occurred at Alaska Peninsula estuaries where species previously unrecorded, including earliest Alaska record, a bird at Port Heiden 24 Apr (Tobish and Isleib 1992a Tobish, Jr., T. G. and M. E. Isleib. (1992a). Alaska Region. American Birds 46:462-465. Close ), and several groups of 1–6 seen 2–23 May (UAM unpubl., REG); occurrence apparently related to late spring throughout w. Alaska and near-record late snow on northern breeding area that year (REG). Elsewhere in Alaska, small numbers regularly recorded early May at n. Gulf of Alaska (Middleton I., Kachemak Bay), 900–1,100 km east of breeding range (West 1993a West, G. C. (1993a). Shorebird guide for Kachemak Bay and Homer, Alaska. Homer, AK: Birchside Studios. Close , UAM unpubl.).

Before 1998, only one verified record from Pacific Northwest, a bird collected on Vancouver I., British Columbia, 31 May 1969 (Richardson 1970 Richardson, F. (1970). A North American record of the Bristle-thighed Curlew outside Alaska. Auk 87:815. Close ). Six other records from Pacific Northwest, 3 each from spring and fall, possibly valid (Paulson 1993 Paulson, D. R. (1993). Shorebirds of the Pacific Northwest. University of Washington Press, Seattle, Washington, USA. Close , Mlodinow et al. 1999 Mlodinow, S. G., S. Feldstein and B. Tweit. (1999). The Bristle-thighed Curlew landfall of 1998: climatic factors and notes on identification. Western Birds 30:133-155. Close ). Unprecedented “fallout” of ≥13 birds (perhaps up to 25) along Pacific Coast from Point Reyes, CA, to Tatoosh I., WA, 6–25 May 1998, coincided with extreme weather over Pacific Ocean that presumably pushed birds far east of normal migration path (Mlodinow et al. 1999 Mlodinow, S. G., S. Feldstein and B. Tweit. (1999). The Bristle-thighed Curlew landfall of 1998: climatic factors and notes on identification. Western Birds 30:133-155. Close ).

Fall

Stages from Jun to Aug along coastal Yukon Delta (Handel and Dau 1988 Handel, C. M. and C. P. Dau. (1988). Seasonal occurrence of migrant Whimbrels and Bristle-thighed Curlews on the Yukon-Kuskokwim Delta, Alaska. Condor 90:782-790. Close ); small groups occur Jul-Aug along coastal Seward Peninsula (Kessel 1989 Kessel, B. (1989). Birds of the Seward Peninsula, Alaska: Their Biogeography, Seasonality and Natural History. University of Alaska Press, Fairbanks, AK, USA. Close ). Best information from study conducted 1975–1979 at central Yukon Delta (Handel and Dau 1988 Handel, C. M. and C. P. Dau. (1988). Seasonal occurrence of migrant Whimbrels and Bristle-thighed Curlews on the Yukon-Kuskokwim Delta, Alaska. Condor 90:782-790. Close ). Birds typically arrive in 2 or 3 peaks mid-Jun to early Aug. First arrivals probably early failed breeders or nonbreeders followed by late failed breeders and then successful breeders and juveniles; first juveniles seen 26 Jul. At Neva Creek (1988–1992), failed nesters left study area in mid-Jun, successful nesters in late Jul, and most juveniles during first week of Aug (REG, TLT). Latest departures from Yukon Delta typically 8–31 Aug (Handel and Dau 1988 Handel, C. M. and C. P. Dau. (1988). Seasonal occurrence of migrant Whimbrels and Bristle-thighed Curlews on the Yukon-Kuskokwim Delta, Alaska. Condor 90:782-790. Close ). Latest record on Yukon Delta 10 Sep (REG, BJM); latest Alaska record 5 Oct on Middleton I. (UAM unpubl.).

Use of Seward Peninsula during postbreeding period poorly known; small numbers of Bristle-thighed Curlews recorded along northern and southern coasts of peninsula in Jul and Aug, including Safety Sound, 3 birds, 22 Jun 1970; Cape Espenberg, 1 and 3 birds, 30 Jun 1976 and 3 Jul 1973, respectively; Lopp Lagoon, 1 and 11 birds, 3 Jul 1974 and 12 Jul 1974, respectively (Kessel 1989 Kessel, B. (1989). Birds of the Seward Peninsula, Alaska: Their Biogeography, Seasonality and Natural History. University of Alaska Press, Fairbanks, AK, USA. Close ). Latest specimen a juvenile male from Safety Sound, 1 Sep 1911 (U.S. Natl. Mus. 2339810; Kessel 1989 Kessel, B. (1989). Birds of the Seward Peninsula, Alaska: Their Biogeography, Seasonality and Natural History. University of Alaska Press, Fairbanks, AK, USA. Close ). Farther north, C. Townsend shot juvenile at Kobuk River mouth near Kotzebue 26 Aug 1885 (Ridgway 1919 Ridgway, R. (1919). The birds of North and Middle America: A descriptive catalogue of the higher groups, genera, species, and subspecies of birds known to occur in North America, Part 8. U.S. National Museum Bulletin 50. Close ), and R. Beck collected “quite a series” of birds near Nome in Aug 1911 (Bent 1929 Bent, A. C. (1929). Life histories of North American shorebirds, Part 2. United States National Museum Bulletin 146. Close ). Nine curlews seen 19 Aug 1988 near Cape Krusenstern, AK (UAM unpubl.), almost certainly juveniles, but ages unknown.

Limited information from 4 adults (2 successful nesters, 2 failed) radio-tagged on breeding grounds in 1989 suggests length of stay on Yukon Delta staging area 2–3 wk (TLT, REG, BJM). Nushagak Peninsula area, n. Bristol Bay, only other site where curlews known to occur in late summer (Murie 1959 Murie, O. J. (1959). Fauna of the Aleutian Islands and Alaska Peninsula. North American Fauna no. 61. U.S. Fish and Wildlife Service, Washington, DC, USA. Close , T. Pogson unpubl.), but extent and duration unknown. Paucity of Jul–Sep records elsewhere in Alaska (e.g., none on Aleutian Is.; occasional on Alaska Peninsula, Pribilof Is., Kodiak I., Nunivak I., Kachemak Bay) indicates migration to wintering islands largely direct from w. Alaska (UAM unpubl., R. MacIntosh unpubl., REG, BJM, TLT).

Based on specimens, Stickney (Stickney 1943 Stickney, E. H. (1943). Birds collected during the Whitney South Sea Expedition: Northern shore birds in the Pacific. American Museum Novitates 1248. Close ) posited that southbound birds arrive in Oceania from late Jul to early Aug. Presumed migratory influxes noted Jul–Sep in Northwestern Hawaiian Is. (Woodward 1972b Woodward, P. W. (1972b). The natural history of Kure Atoll, Northwestern Hawaiian Islands. Atoll Research Bulletin 164. 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 , Clapp and Wirtz Clapp and Wirtz II 1975 Clapp, R. B., and W. O. Wirtz II (1975). The natural history of Lisianski Island, northwestern Hawaiian Islands. Atoll Research Bulletin 186. Close ) and Sep–Oct in Line Is. (Kirby 1925 Kirby, Jr., H. (1925). The birds of Fanning Island, central Pacific Ocean. Condor 27:185-197. Close , Gallagher 1960 Gallagher, M. D. (1960). Bird notes from Christmas Island, Pacific Ocean. Ibis 102 (4):489-502. Close ) and Samoa (Muse and Muse 1982 Muse, C. and S. Muse. (1982). The birds and birdlore of Samoa. Walla Walla, WA: Pioneer Press. Close ). These and other reports of southbound “arrivals” based on unmarked birds of unknown age. Arrival of migrants on wintering grounds best known from study at Laysan I., Northwestern Hawaiian Is., 1988–1991 (Marks and Redmond 1994b Marks, J. S. and R. L. Redmond. (1994b). Migration of Bristle-thighed Curlews on Laysan Island: timing, behavior and estimated flight range. Condor 96:316-330. Close ). Adults arrived in 2 peaks, first 18–24 Jul and second 16–23 Aug; all returning marked adults arrived by first week of Sep. Juveniles arrived mid-Aug to early Sep, earliest 19 Aug. Several arriving flocks consisted entirely of juveniles (JSM), and arrival dates of adults versus juveniles strongly suggest that juveniles undertake southward migration unaccompanied by adults (contra Johnsgard 1981 Johnsgard, P. A. (1981) The plovers, sandpipers, and snipes of the world. University of Nebraska Press, Lincoln, Nebraska. Close , Hayman et al. 1986 Hayman, P., J. Marchant, and T. Prater (1986) Shorebirds: an identification guide to the waders of the world. Houghton Mifflin Company, Boston, Massachusetts, USA. Close ; see Marks and Redmond 1994b Marks, J. S. and R. L. Redmond. (1994b). Migration of Bristle-thighed Curlews on Laysan Island: timing, behavior and estimated flight range. Condor 96:316-330. Close ).

Inter-island Movements

Amadon (Amadon 1953b Amadon, D. (1953b). Migratory birds of relict distribution: some inferences. Auk 70:461-469. Close ) speculated that Bristle-thighed Curlews stopped in Hawaiian Is. and eventually wintered farther south. Based on counts of unmarked birds in spring and fall, Amadon's view supported for Northwestern Hawaiian Is. (Amerson 1971 Amerson, A. B. (1971). The natural history of French Frigate Shoals, Northwestern Hawaiian Islands. Atoll Research Bulletin 150:1-383. Close , Woodward 1972b Woodward, P. W. (1972b). The natural history of Kure Atoll, Northwestern Hawaiian Islands. Atoll Research Bulletin 164. 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 , Amerson et al. 1974 Amerson, A. B., Jr, R. C. Clapp and III W. O. Wirtz. (1974). The natural history of Pearl and Hermes Reef, Northwestern Hawaiian Islands. Atoll Research Bulletin 174. Close , Clapp and Wirtz Clapp and Wirtz II 1975 Clapp, R. B., and W. O. Wirtz II (1975). The natural history of Lisianski Island, northwestern Hawaiian Islands. Atoll Research Bulletin 186. Close ) and echoed by Handel and Dau (Handel and Dau 1988 Handel, C. M. and C. P. Dau. (1988). Seasonal occurrence of migrant Whimbrels and Bristle-thighed Curlews on the Yukon-Kuskokwim Delta, Alaska. Condor 90:782-790. Close ). Studies of marked birds, however, show that Northwestern Hawaiian Is. are migratory terminus rather than stopover, and that most curlews wintering farther south overfly Hawaiian Is. in spring and fall (Marks and Redmond 1994b Marks, J. S. and R. L. Redmond. (1994b). Migration of Bristle-thighed Curlews on Laysan Island: timing, behavior and estimated flight range. Condor 96:316-330. Close ). High counts of curlews in Northwestern Hawaiian Is. in spring and fall result from flocking of local birds at traditional roost sites rather than influxes of transients (see below). Bristle-thighed Curlew banded on Lisianski I. 25 Sep 1967 (Clapp and Wirtz Clapp and Wirtz II 1975 Clapp, R. B., and W. O. Wirtz II (1975). The natural history of Lisianski Island, northwestern Hawaiian Islands. Atoll Research Bulletin 186. Close ) and found in Marshall Is. in 1981 (Dunning 1988a Dunning, Jr., J. B. (1988a). Significant encounters with marked birds. North American Bird Bander 13:9. Close ) is only record of bird from Northwestern Hawaiian Is. occurring in tropical Pacific outside Hawaiian Is.

Three marked adults from Laysan I. seen on main Hawaiian Is. during southward migration, including bird on O‘ahu 8 Aug 1990 that reoriented to Laysan I. and wintered there (JSM). Adults highly faithful to 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 ), but numerous records of marked birds moving among islands in Northwestern chain, especially 2-yr-olds (i.e., 24–27 mo old) that move in late summer at same time adults are migrating south (JSM).

Data from Laysan I. in spring 1991 (Marks and Redmond 1994b Marks, J. S. and R. L. Redmond. (1994b). Migration of Bristle-thighed Curlews on Laysan Island: timing, behavior and estimated flight range. Condor 96:316-330. Close ). No pattern in daily timing of departures, with half of flocks leaving before 14:00 and half after (n = 16 departures). Earliest departure at 09:10 on 7 May and latest at 17:30 on 6 May; no significant relationship between daily timing and date of departure. Unlike in other shorebirds (Lank 1989 Lank, D. B. (1989). Why fly by night? Inferences from tidally-induced migratory departures of shorebirds. Journal of Field Ornithology 60:154-161. Close , Alerstam et al. 1990 Alerstam, T., G. A. Gudmundsson, P. E. Jönsson, J. Karlsson and Å. Lindström. (1990). Orientation, migration routes and flight behaviour of Knots, Turnstones and Brant Geese departing from Iceland in spring. Arctic 43:201-214. Close , Piersma et al. 1990b Piersma, T., L. Zwarts and J. H. Bruggemann. (1990b). Behavioural aspects of the departure of waders before long-distance flights: flocking, vocalizations, flight paths and diurnal timing. Ardea 78:157-184. Close ), diurnal timing of Bristle-thighed Curlew departures unrelated to tidal cycle or sunset.

Just prior to departing, typically stopped at staging site at north end of Laysan I., a spot not used by curlews at other times of year (JSM). Only 4 of 16 departing flocks failed to stop at staging site; these flocks among latest to depart island (9–13 May). Other 12 flocks stopped at staging site for 7–75 min (mean 36 min). Staging birds typically stood quietly in loose flock, facing north. Departures always preceded by increased vocal activity; flocks circled above island as they gained altitude, with birds uttering chiu-eet and klee calls incessantly (see Sounds and Vocal Behavior: Vocalizations, below). All departing flocks flew to north or north-northwest in loose cluster and then formed Vs or echelons, continuing to ascend before disappearing from view.

Some members of departing flocks (5–62%) returned to island in 12 of 16 departures. Nine of these returning flocks scrutinized for color-bands; 58–100% of birds individually marked, and each flock had 1- and 2-yr-olds that were noticeably thinner than adults. These subadults made up large proportion of birds that returned to island after departures. Mean size of flocks 14.1 at first departure (range 1–31) and 10.7 for birds disappearing from view (range 1–22). Mean flock size experienced by average bird (Ýg2/Ýg, where g = flock size) 20.5 and 16.2 for departing and disappearing flocks, respectively. Sizes of departing flocks substantially smaller than in other shorebird species (Alerstam et al. 1990 Alerstam, T., G. A. Gudmundsson, P. E. Jönsson, J. Karlsson and Å. Lindström. (1990). Orientation, migration routes and flight behaviour of Knots, Turnstones and Brant Geese departing from Iceland in spring. Arctic 43:201-214. Close , Blomert et al. 1990 Blomert, A. M., M. Engelmoer and Y. Ntiamoa-Baidu. (1990). The Banc D'Arguin, Mauritania, as a meeting point for Avocets during spring migration. Ardea 78:185-192. Close ), despite theoretical benefits of large flock size at departure (Piersma et al. 1990b Piersma, T., L. Zwarts and J. H. Bruggemann. (1990b). Behavioural aspects of the departure of waders before long-distance flights: flocking, vocalizations, flight paths and diurnal timing. Ardea 78:157-184. Close ).

Upon arrival at Laysan I. from Alaska, incoming birds highly vocal, being audible from >1 km as flocks descend to island (JSM). First landing by adults and juveniles typically occurs at traditional roosting site at south end of island, where curlews congregate year-round (although numbers highest in spring and fall; JSM, Marks and Redmond 1994b Marks, J. S. and R. L. Redmond. (1994b). Migration of Bristle-thighed Curlews on Laysan Island: timing, behavior and estimated flight range. Condor 96:316-330. Close ). Arriving birds invariably drink seawater from tide pools at roosting site within minutes of landing (JSM).

Migrating Bristle-thighed Curlews presumably do not land on water and thus fly night and day. Altitude and flight speed during migration unknown. Based on radar studies, shorebirds fly at altitudes up to 6 km and at ground speeds >70 km/h (Williams and Williams Williams and Williams 1988 Williams, T. C., and J. M. Williams (1988). Radar and visual observations of autumnal (southward) shorebird migration on Guam. Auk 105:460–466. Close , Williams and Williams 1990 Williams, T. C., and J. M. Williams (1990). The orientation of transoceanic migrants. In Bird Migration: Physiology and Ecophysiology (E. Gwinner, Editor). Springer-Verlag, Berlin, Germany. pp. 7–21. Close ). Birds flying from Laysan I. at 75 km/h (Castro and Myers 1989 Castro, G. and J. P. Myers. (1989). Flight range estimates for shorebirds. Auk 106:474-476. Close ) would reach Alaska in 53 h.

Clearly a calendar migrant in spring, based on narrow time window of departure from Laysan I. and arrival in Alaska. On Laysan I., color-banded curlew with broken wing traversed entire island on foot (>3 km) and staged with volant curlews during peak of northward migration, later returning to home range (Marks 1995 Marks, J. S. (1995). Migratory behaviour of curlews with broken wings. Wader Study Group Bulletin 76:37-38. Close ). This injury was ≥1.5 yr old, yet bird deposited fat and “migrated,” indicating that spring migration controlled by endogenous circannual clock (Marks 1995 Marks, J. S. (1995). Migratory behaviour of curlews with broken wings. Wader Study Group Bulletin 76:37-38. Close ). Marked adult with leg injury that affected foraging rate and slowed molt made ≥3 migratory flights between Laysan I. and Alaska (Marks and Underhill 1994 Marks, J. S. and L. G. Underhill. (1994). Moult, migration and mass of a handicapped Bristle-thighed Curlew Numenius tahitiensis. Ardea 82:153-155. Close ).

Gains mass steadily throughout winter following completion of molt in late autumn (Marks 1993 Marks, J. S. (1993). Molt of Bristle-thighed Curlews in the northwestern Hawaiian Islands. Auk 110:573-587. Close ), unlike other shorebirds that maintain low mass in winter and fatten rapidly in spring (e.g., Pienkowski et al. 1979 Pienkowski, M. W., C. S. Lloyd and C. D. T. Minton. (1979). Seasonal and migrational weight changes in Dunlins. Bird Study 26:134-148. Close , Summers and Waltner 1979 Summers, R. W. and M. Waltner. (1979). Seasonal variations in the mass of waders in southern Africa, with special reference to migration. Ostrich 50:21-37. Close ). Presumed gradual accumulation of fat thought to result from relatively unproductive foraging conditions on oceanic islands that preclude rapid fattening in spring (Marks 1993 Marks, J. S. (1993). Molt of Bristle-thighed Curlews in the northwestern Hawaiian Islands. Auk 110:573-587. Close ). Six adults collected at Laysan I. and Midway Atoll during peak of spring migration had lipid indices (fat mass/body mass) ranging from 36.3 to 47.0% (mean 42.5%), among highest fat loads ever measured in shorebirds (Marks and Redmond 1994b Marks, J. S. and R. L. Redmond. (1994b). Migration of Bristle-thighed Curlews on Laysan Island: timing, behavior and estimated flight range. Condor 96:316-330. Close , Piersma and Gill 1998 Piersma, T., and R. E. Gill Jr. (1998). Guts don't fly: Small digestive organs in obese Bar-tailed Godwits. Auk 115:196–203. Close ). Lipid indices of 7 curlews collected mid-Jul 1973 on Eniwetok Atoll ranged from 3.3 to 10.8% (Johnson and Morton 1976 Johnson, O. W., and M. L. Morton (1976). Fat content and flight range in shorebirds summering on Enewetak Atoll. Condor 78:144–145. Close ); birds appeared to be subadults based on molt (Johnson 1977a Johnson, O. W. (1977a). Plumage and molt in shorebirds summering at Enewetak Atoll. Auk 94:222-230. Close , Marks 1993 Marks, J. S. (1993). Molt of Bristle-thighed Curlews in the northwestern Hawaiian Islands. Auk 110:573-587. Close ) and thus were in nonmigratory state.

Measurements from the 6 birds collected in Northwestern Hawaiian Is. indicate that Bristle-thighed Curlews reduce size of gizzard, intestines, and liver in preparation for transoceanic flights (see Piersma 1998 Piersma, T. (1998). Phenotypic flexibility during migration: optimization of organ size contingent on the risks and rewards of fueling and flight. Journal of Avian Biology 29:511-520. Close , Piersma and Gill 1998 Piersma, T., and R. E. Gill Jr. (1998). Guts don't fly: Small digestive organs in obese Bar-tailed Godwits. Auk 115:196–203. Close ). Stomachs of these birds empty, consistent with observations that Bristle-thighed Curlews forgo foraging for at least 1 d before migratory departure (Marks and Redmond 1994b Marks, J. S. and R. L. Redmond. (1994b). Migration of Bristle-thighed Curlews on Laysan Island: timing, behavior and estimated flight range. Condor 96:316-330. Close , JSM).

Based on lipid indices of these 6 birds, flight-range estimates of 3,000–10,000 km (Marks and Redmond 1994b Marks, J. S. and R. L. Redmond. (1994b). Migration of Bristle-thighed Curlews on Laysan Island: timing, behavior and estimated flight range. Condor 96:316-330. Close ). Lower estimates clearly wrong, given that curlews were about to fly 4,000 km over ocean, whereas upper estimates perhaps unrealistically far. However, recent evidence that Bar-tailed Godwits capable of flying 11,000 km nonstop (Piersma and Gill 1998 Piersma, T., and R. E. Gill Jr. (1998). Guts don't fly: Small digestive organs in obese Bar-tailed Godwits. Auk 115:196–203. Close ) raises possibility that Bristle-thighed Curlews fly nonstop to southern end of winter range >8,500 km from Alaska. Likely that assistance from winds aloft important factor in transoceanic migration (Piersma and Sant 1992 Piersma, T. and S. van de Sant. (1992). Pattern and predictability of potential wind assistance for waders and geese migrating from West Africa and the Wadden Sea to Siberia. Ornis Svec. 2:55-66. Close , Marks and Redmond 1994b Marks, J. S. and R. L. Redmond. (1994b). Migration of Bristle-thighed Curlews on Laysan Island: timing, behavior and estimated flight range. Condor 96:316-330. Close ).