SPECIES

Bristle-thighed Curlew Numenius tahitiensis Scientific name definitions

Jeffrey S. Marks, T. Lee Tibbitts, Robert E. Gill, and Brian J. McCaffery
Version: 1.0 — Published March 4, 2020
Text last updated January 1, 2002

Breeding

Phenology

Pair Formation

Spring migrants usually arrive singly or in groups of 2, occasionally in flocks (largest 38). Over 3-yr period at Neva Creek, both members of most pairs (73%, n = 55 within-pair comparisons) first observed on same date but not necessarily in same vicinity. Females never observed before mates in same year; males seen 1–6 d before mates. Over 3-yr period in Nulato Hills, both members first observed on same date in 3 pairs, male preceded female (by 1–6 d) in 7 pairs, and female preceded male by 1 d in 1 pair.

Nest-Building

Paired birds and unpaired males observed nest-scraping within 1–3 d of arrival. Addition of nest-lining continues during egg-laying.

First/Only Brood Per Season

Figure 5 . At Nulato Hills (1987–1991), clutch initiation 17 May–9 Jun (n = 23); median clutch initiation (all years combined) 26 May. Most nests (19 of 23) initiated last 2 wk of May. Thirteen successful nests (from 5 different site-years) hatched from 15 to 30 Jun (greatest within-year span in hatching dates also 15–30 Jun). Elsewhere in southern breeding area (Allen Creek), size of captured chicks indicated hatching in late year (1992) delayed until 25 Jun–10 Jul (REG, BJM). At Neva Creek (1989–1993), clutch initiation 18 May–18 Jun (based on direct observation or backdating from estimated hatching dates; n = 79); median clutch initiation 24–31 May (n = 5 yr), about 2 wk after arrival of females. Late clutches (initiated 9–18 Jun) attributable to late-arriving females rather than renesting attempts. Over same 5-yr period, median hatching dates 22–28 Jun, with only a few nests hatching in Jul (latest 17 Jul). Between 95% and 100% of pairs hatched within 8–10 d in 2 early years and 21–22 d in 1 late year at Neva Creek.

Second Brood Per Season

Not known to occur. Replacement clutch after first failed suspected ≥2 times but could not be confirmed (BJM, TLT).

Nest Site

Selection Process

No information.

Microhabitat And Site Characteristics

See Distribution and Habitat: Habitat in Breeding Range, above. Nests placed on ground, often well concealed by low vegetation and generally difficult to detect owing to adult's cryptic plumage and secretive behavior. Most nests found in dwarf-shrub meadows (Allen and Kyllingstad 1949, BJM, TLT, REG); mean distance to nearest shrub thicket 38.0 m (range 7.9–96.6) at Nulato Hill (n = 14 nests) and 8.4 m (range 0.2–93.0) at Neva Creek (n = 16). In Nulato Hills, nests found beneath dwarf willows more likely to hatch; 4 of 5 located under willows hatched, whereas only 5 of 15 without adjacent willows hatched (McCaffery and Gill 1992, BJM). Among nests not sheltered by overhead willow, most still with lateral protection. At Curlew Lake, nests protected by a hummock or shrub located <50 cm away on an average of 4.1 (of 8 possible) aspects (BJM); the first 2 nests known to science were placed “by the side of a hummock” (Allen and Kyllingstad 1949: 345). All nests at Neva Creek (n = 16) sheltered on 1–3 of 4 principal aspects by tussocks (usually by old or decaying plants) and/or shrubs and sedges 10–25 cm tall.

Vegetative cover and species richness highly variable within 1-mplots centered on nest bowls (n = 14 at Nulato Hills and n = 16 at Neva Creek). Total vegetative cover at Nulato Hills 4–49% dwarf shrubs, 5–35% herbaceous plants, 1–60% moss, and 5–89% lichens. Species richness at both Curlew Lake and Neva Creek 1–2 species of mosses, 1–3 species of lichens, and 1–13 species of vascular plants. Shrub species most commonly observed at Neva Creek nests: dwarf birch 94% of nests, willows 94%, Labrador tea 88%, black crowberry 63%, and lingonberry 56%. Nests at Neva Creek were 15–330 m from nearest creek or river. See photos in Gill et al. 1988 and McCaffery and Gill and Redmond 1992 for examples of vegetation at nest sites.

Nest

Construction Process

Male selects sites for ritualized prenesting displays (see Behavior: Sexual Behavior, above) and creates scrape by lowering breast to ground, rubbing it back and forth, kicking out material with feet, and repeating these actions as he pivots in bowl. Both sexes add material (e.g., bits of lichen) and work on nest during displays. Not known if female visits nest in absence of male; no information on selection of ultimate nest site.

Structure And Composition Matter

Typical of most Numeniini. A rather deep depression in tussock or moss with thick layer of material in bottom (contra Baicich and Harrison 1997), mostly decayed leaves (e.g., willow, birch, blueberry), lichen (particularly Cetraria cucullata), and fragments of mosses, sedges, and twigs (Allen and Kyllingstad 1949, BJM, TLT, REG). Most materials lining nest present in immediate vicinity (TLT; but see Allen and Kyllingstad 1949); materials continue to be added during incubation (J. Pearce pers. comm.).

Dimensions

Of 16 nests at Neva Creek, mean outside diameter 188 mm ± 15 SD (range 160–235); mean depth (with lining) 62 mm ± 9 SD (range 50–85); lining from 12 nests 5–40 mm thick. Elsewhere, 2 nest bowls near Curlew Lake were 172 and 178 mm across and 64 and 83 mm deep, respectively (Allen and Kyllingstad 1949).

Microclimate

No information.

Maintenance Or Reuse Of Nests, Alternate Nests

No birds known to reuse previous year's nest bowl (n = 11; TLT, BJM).

Nonbreeding Nests

Male may construct multiple nest scrapes on territory.

Eggs

Shape

Ovate pyriform (Allen and Kyllingstad 1949, REG).

Size

For 16 eggs from 7 clutches (5 Neva Creek; 2 in Allen and Kyllingstad [Allen and Kyllingstad 1949]), mean length 60.4 mm ± 2.50 SD (range 57.5–65.0); mean breadth 42.5 mm ± 1.00 SD (range 41.5–44.7).

Mass

From single clutch of 4 eggs found mid-incubation, mean mass 55.9 g ± 2.5 SD (range 52.3–57.8), mean volume 55.1 ml ± 2.8 SD (range 51.0–57.0). Clutch mass about 53% of average female body mass during incubation (REG).

Color

Described by Allen and Kyllingstad (Allen and Kyllingstad 1949) from terminology of Ridgway (Ridgway 1912) as buffy brown with spots of mummy brown; also noted that egg color changed within several months of collection, ground color becoming buffy olive and spotting light-brownish drab to bistre or raw umber. Following references to color names and numbers after Smithe 1975 . From single fresh clutch at Neva Creek, ground color generally Grayish Horn (91) with markings of Raw Umber (223), Prout's Brown (121A), and Vandyke Brown (121). From large intact shell fragments of hatched eggs (n = 10 nests; eggs stored in dark) at Neva Creek examined several years after collection, ground color quite variable (both among and within clutches), but mostly Raw Umber, Light Drab (119C), Dark Drab (119B), Tawny Olive (223D), Grayish Horn, or Smoke Gray (45). Markings similarly variable, including Natal Brown (219A), Warm Sepia (221A), Sepia (219), Mars Brown (223A), Raw Umber, Burnt Sienna (132), Army Brown (219B), Fuscous (21), Prout's Brown, and Vandyke Brown. Markings (spots, splotches, squiggly lines) scattered over entire egg but concentrated at larger end. Photographs of eggs appear in Allen and Kyllingstad 1949 and McCaffery and Gill 1992 .

Surface Texture

Slightly glossy, becoming glossier as incubated (REG).

Eggshell Thickness

From eggs collected at Neva Creek in 1992–1993 (3 clutches, 8 eggs, shell plus membranes at equator, 6–12 measurements per egg; REG), mean thickness per egg 0.239 mm ± 0.0058 SD (range 0.232–0.250).

Clutch Size

Usually 4. See Demography and Populations: Measure of Breeding Activity, below.

Egg-Laying

Little information. Appears to take 5 d to lay 4-egg clutch; interval between eggs 1–2 d (BJM).

Incubation

Onset Of Broodiness And Incubation In Relation To Laying

Observations of males and females flushed from nests containing 2 and 3 eggs suggest incubation begins before clutch completion. One pair tended initial 2 eggs of clutch for 95% of 10-h period (BJM).

Incubation Patches

Both sexes with 2 large, elliptical patches, 1 on each side of belly midline; likely develop at onset of incubation (REG). Not known when patches recede.

Incubation Period

Average 24 d from laying of fourth egg until start of hatching (range 22–26, n = 5).

Parental Behavior

Incubation shared by both parents (BJM, REG, TLT). One incubating male was completely motionless for 61-min observation period; during other periods only moved when repositioning eggs (3 and 8 times during 2- and 4-h observation periods, respectively). Same bird did not move or vocalize when avian predators flew through territory (J. Pearce pers. comm.). Based on repeated visits to nests and timing of sightings in communal flocks of off-duty birds, no apparent sex-specific diel incubation pattern (neither between pair members nor within local populations), but needs study (TLT, REG). Beginning 2–3 d before hatching, nest occasionally left unattended for short periods while adult(s) forages nearby (TLT).

Hardiness Of Eggs

Information limited. Both study areas occasionally covered by snow in spring; if during laying, eggs must get covered with snow for day or more, but such events usually occur when daytime temperatures above freezing (REG, BJM, TLT). Effect on hardiness of eggs unknown.

Hatching

Preliminary Events And Vocalizations

No information.

Shell Breaking And Emergence

About 3 d between first crack in egg (star pip) and hatching (BJM).

Parental Assistance And Disposal Of Eggshells

No information. Variable amounts of eggshells found in recently hatched nests; often large pieces of each egg remain (BJM, TLT).

Young Birds

Condition At Hatching

See Appearance: Hatchlings, above. Chicks precocial and nidifugous, covered in down, eyes open. Chicks lose egg tooth either in nest or within day of leaving nest (TLT). For chicks captured 1–24 h after hatching, average body mass 37.6 g ± 2.7 SD (n = 17 from 8 broods); exposed culmen 17.0 mm ± 2.1 SD (n = 9 from 5 broods); and diagonal tarsus 38.2 mm ± 2.5 SD (n = 13 from 5 broods; REG, TLT). Culmens of hatchlings about 18%, and tarsi about 64%, of adult length (sexes averaged; REG).

Departure From Nest

Young depart nest within 12 h of all eggs hatching (n = 7 nests; REG, TLT). Parents lead chicks by repeatedly walking or flying short distances and calling chicks toward them. Broodmates stay close together for at least first day out of nest but soon disperse; siblings 5–8 d old found >50 m apart. At Neva Creek during first week posthatching, broods move upslope; linear distances moved/brood extremely variable, averaging 325–1,000 m/d in given season. Extreme by single brood 2.2 km over 2–3 d (Lanctot et al. 1995). At Curlew Lake, maximum brood movements 2.6 km in 27 h and 3.8 km in 50 h (BJM).

Growth And Development

Chicks grow rapidly, especially during second week; mean mass 43.7 g ± 9.5 SD at 2–6 d old (n = 36 from 19 broods) and 180.9 g ± 67.4 SD at 8–15 d old (n = 9 from 9 broods; REG, TLT). One 2-d-old chick gained 1 g in 3 d (from 38 to 39 g), and 14-d-old chick gained 5 g in 2 d (from 230 to 235 g). Time between hatching and first flight 21–24 d (Lanctot et al. 1995); time between hatching and independence 33–41 d (REG, TLT).

Parental Care

Very active and aggressive parental care. Both parents care for chicks for 3–4 wk, after which many adults depart, leaving broods in aggregations that are tended by small numbers of adults. One of only a few shorebird species to exhibit brood amalgamation (see below).

Brooding

Both parents brood. Chicks brooded in nest for up to several hours after hatching, thereafter outside of nest for short periods at frequent intervals (largely dependent on ambient temperature) over next 4–7 d (Gill et al. 1991). From about 1–7 d of age, chicks respond to predators by crouching, freezing, and remaining silent while parents attack-mob predator. Parent-chick brooding bond very strong during first week posthatching, e.g., captured adults assume brooding posture and give Brooding Calls in holding bag upon hearing Peep Calls of nearby chicks (REG, TLT).

Brood-Rearing

From Lanctot et al. 1995 . Within day of hatching, parents lead broods upslope away from nest. Parents defend wide radius around brood, attack-mobbing potential predators and chasing away conspecific adults and other shorebirds. As season progresses, most families engage in complex process of brood amalgamation. Process entails 4 stages over 4–5 wk. (1) Early stage, during which broods form temporary, incidental associations that develop shortly after hatching (median 4 d, range 2–11, n = 11 broods), persist <3 d, involve ≥2 adjacent (<200 m) broods, and entail alloparental care vis-à-vis defense against predators. (2) Intermediate stage 2–3 wk posthatching, during which adult desertion of young first occurs and many broods become clumped; about half of broods participate in extended associations in which pairs spend ≥6 d together, move around as a group, and receive alloparental care. (3) Late stage 4–5 wk posthatching, when most young volant, most parents have departed, and broods are tightly clumped; such aggregations usually tended by single adult male (his offspring always present) for additional 5 d after other male parents have departed. (4) Independent stage, when all young are volant and in flocks for additional 2–6 d before departing breeding area and after last adult male(s) has departed. About half of 27 broods that successfully fledged during 3-yr period at Neva Creek participated in early and/or intermediate stage associations; all were part of a late stage aggregation. Brood amalgamation appears widespread; broods at Nulato Hills traveled to same site across years and occurred in early and intermediate stage associations; predators scattered young and/or depredated them before aggregations could form (BJM).

Feeding

Chicks feed themselves by pecking and jabbing at objects. Initially, both parents tend broods and lead them to foraging areas (Lanctot et al. 1995); later, alloparent(s) presumably assumes this role.

Nest Sanitation

Not applicable.

Carrying Of Young

Not known to occur.

Cooperative Breeding

Not known to occur.

Brood Parasitism by Other Species

Not known to occur.

Fledgling Stage

Departure From Nest

See Young birds, above.

Growth

See Young birds, above. Five just volant fledglings (22–27 d old) had attained 77% of average mass of breeding adults (sexes combined), 44% of adult bill length, 105% of tarsal length, and 70% of wing length (REG, TLT). Juveniles continue to grow during first year posthatching; e.g., on Laysan I., birds 10–11 mo old with culmen and wings 88% and 90%, respectively, of breeding adult lengths (n = 166; data pooled for both sexes).

Association With Parents Or Other Young

See Parental care, above. Most parents remain with chicks until a few days before fledging; thereafter, male (1 exception in 20 marked pairs, see below) or male alloparent defends chicks and fledglings against predators, but only until young capable of strong flight (Lanctot et al. 1995, BJM). At Neva Creek, females of fledged broods always deserted before males; median number of days of brood attendance for males and females was 29 and 23, 32 and 28, and 25 and 23, respectively, during 1990–1992 (Lanctot et al. 1995). Information from Nulato Hills equivocal (BJM); of 2 pairs that fledged young, female attended brood longer than male in 1 case (27 versus 24 d), and male attended brood longer in another (41 versus 21 d); also, in 1 pair where brood taken by predator late in brood-rearing, female attended brood 4 d longer than male (22 versus 18 d). At least until fledging, siblings always together. Extent of sibling associations after fledging unknown, but extensive sightings of marked birds suggest juveniles remain with same brood aggregation (only one observation of juvenile switching aggregations, this after alloparent departed aggregation; TLT). Extent of sibling association after leaving breeding grounds unknown; observation of entire brood aggregation (n = 20 juveniles) departing Neva Creek as flock (J. Pearce pers. comm.) suggests association at least through initial stages of migration.

Immature Stage

Immatures stay on brood-rearing areas 2–6 d after last adults depart (Lanctot et al. 1995), where regularly associate with juvenile conspecifics and Bar-tailed Godwits from own and nearby brood aggregations. Flocks of juveniles engage in frequent local flights within 8-km radius of area; often do not react defensively to avian predators and are easily approached by humans. Arrive on Yukon Delta staging grounds about 2 wk after adults have reached peak numbers (Handel and Dau 1988); there comingle with adults for about 3 wk before departing (TLT, REG).

Bristle-thighed Curlew Figure 5. Annual cycle of molt, breeding, and migration of the Bristle-thighed Curlew.
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Figure 5. Annual cycle of molt, breeding, and migration of the Bristle-thighed Curlew.

Thick lines show peak of activity; thin lines, off-peak. Molt data from Laysan I. (Marks 1993 ).

Bristle-thighed Curlew Nesting habitat; Alaska, June.
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Nesting habitat; Alaska, June.

Central Seward Peninsula, Alaska.  June 2006.  Curlews nest on tundra-covered slopes of rolling hills intersected with numerous drainages. © Lee Tibbitts; photographer Lee Tibbitts

Bristle-thighed Curlew Bristle-thighed Curlew chick, 1 day old; Seward Peninsula, AK, June
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Bristle-thighed Curlew chick, 1 day old; Seward Peninsula, AK, June

One-day old chick in upland tundra vegetation.  Chicks are highly precocial and capable of walking great distances (100s m/day) within hours of hatch.  © Lee Tibbitts; photographer Lee Tibbitts

Recommended Citation

Marks, J. S., T. L. Tibbitts, R. E. Gill, and B. J. McCaffery (2020). Bristle-thighed Curlew (Numenius tahitiensis), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.brtcur.01