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

Sounds and Vocal Behavior

Introduction

The euphonious cries of the Bristle-thighed Curlew are perhaps the most evocative sounds of w. Alaska's upland tundra. Although several calls are derived from the low whistles characteristic of other curlew species, these simple pure tones are elaborated dramatically in the Bristle-thighed Curlew. Sweeping portamentos, dramatic frequency spikes, and multiple patterns of sequential frequency shifts characterize the nuptial vocalizations of this species. These layers of complexity create a repertoire both aesthetically pleasing and scientifically intriguing. Vocalizations described here by BJM unless referenced otherwise.

Vocalizations

Development

As in Whimbrel (Skeel and Mallory 1996), young chicks produce Peep Calls when attempting to locate parents and a harsh, sibilant Whee Call when threatened or captured (BJM, REG, TLT). Whee Call (see Figure 4A) starts and ends near 2.20 kHz, lasts 720 ms, and peaks near 3.50 kHz for nearly 400 ms. Frequency and amplitude are roughly coupled (BJM). Repertoire develops rapidly; by 3 wk chicks capable of Whines, Growls, and Chiu-eets, although still use Peep Calls frequently, and by 5 wk attempt Complex Whistle (see below); Chiu-eets distinctively hoarse (relative to adults), at least through fall staging (BJM, REG, TLT).

Vocal Array

As in Whimbrel (Skeel and Mallory 1996), Bristle-thighed Curlew Song not distinctive vocalization, but rather a combination of other vocalizations with a distinctive syntax (see below).

A “clear insistent whistle . . . remarkably like human attention whistle” (Sibley 2000); Yup'ik Eskimo name “Chiuit” derived from this call (Kyllingstad 1948). Chiu-eets characterized by smooth, rapid transitions from an initial brief frequency rise through a more pronounced descent and rise in frequency (spanning >1 kHz), to a descending mirror image of the initial frequency rise; generates a U-shaped sonogram, typically more or less symmetrical (e.g., Figure 4A, first female Chiu-eet in Figure 4B). From 16 recorded Chiu-eets (n = 2 individuals), mean duration 386 ms ± 93 SD (range 213–496 ms), mean peak frequency 2.97 kHz ± 0.24 SD (range 2.53–3.23), mean lowest frequency 1.76 kHz ± 0.24 SD (range 1.34–2.16), and mean frequency range 1.22 kHz ± 0.12 SD (range 1.03–1.41). Amplitude varies dramatically (contra Sibley 2000); greatest at start and end of call (although amplitude profiles not necessarily symmetrical), with low-frequency portion always corresponding to lowest amplitude (Figure 4D, first call).

In series of Chiu-eets, calls vary in frequency, amplitude, and rate (and may exhibit sequential gradation in all 3) depending on context (see below). Preliminary analyses indicate sexual variation. Chiu-eets of males higher pitched than those of females owing to differences in fundamental frequencies.

Low Whistle. Homologous with comparable call of Whimbrel (see Skeel 1978); occasionally Low Whistles of 2 species sound virtually identical and very similar to warning beeps of dump trucks in reverse. Much more frequently, however, Low Whistles begin and end with rapidly descending and ascending portamentos, respectively, which may span 1.5 kHz. Phonetically rendered as wiiteew (Sibley 2000). Resulting sonogram structure resembles profile of Viking ship, with portamentos at “bow” and “stern” (see introductory Low Whistle in Figure 4C) and a mean base frequency (i.e., “body” of the ship) of 1.59 kHz ± 0.11 SD (range 1.45–1.83, n = 21; unless specified otherwise, sample sizes reflect number of calls or intervals in 7 songs from 2 individuals). Amplitude patterns need study.

Low Whistles usually given in series (up to 30), and typically introduce Songs (see below); less frequently given without other vocalizations. Low Whistles introducing Songs average 589 ms ± 183 SD (range 327–915, n = 14); those ending Songs average 660 ms ± 247 SD (range 331–1108, n = 8). Intervals between Low Whistles in a series average 161 ms ± 91 SD (range 101–447, n = 13).

Complex Whistle. Elaborates on “Viking ship” structure of typical Low Whistles; phonetically rendered pidl WHIDyooooo (Sibley 2000). Between initial and closing portamentos, Complex Whistles exhibit 1 to several sharp frequency spikes (e.g., 3 in both Complex Whistles of Figure 4C). Primary spikes often followed by conspicuous secondary and even tertiary spikes, usually (but not always) peaking at lower frequency than primary spike. Alternatively, frequency variation immediately following primary spikes may be more subtle (e.g., coarse frequency modulation following primary spikes in Figure 4C). Within Complex Whistle, sequential gradation in peak frequency of primary spikes common. Peak frequencies of primary spikes may rise or fall across Complex Whistle; rarely graded rise and fall within same Complex Whistle.

Among Complex Whistles in Songs, mean base frequency 1.74 kHz ± 0.18 SD (range 1.54–2.45, n = 34); mean duration of Complex Whistles 568 ms ± 199 (range 225–928, n = 27), and mean interval between Complex Whistles 137 ms ± 17 SD (range 100–162, n = 27). Complex Whistles usually given in series; such series typically given in Song (e.g., 2 in Figure 4C; see Song, below) but may be given independently of other vocalizations. Among series of Complex Whistles given in Song, mean peak frequency reached by highest Complex Whistle (invariably at start or end of call) 2.95 kHz ± 0.32 SD (range 2.60–3.39, n = 7 songs), and mean peak frequency of highest primary spike 2.52 kHz ± 0.16 (range 2.40–2.83, n = 7 songs).

Whine. Homologous with similar call of Whimbrel (Skeel 1978) but with gentle modulation across length in frequency and amplitude. Most typical Whine a wavering, plaintive whistle resembling whee-ooo-whee-ooo-whee. Mean duration of 11 Whines (from 3 songs by 3 individuals) 1,071 ms ± 240 SD (range 780–1,710), mean peak frequency 2.49 kHz ± 0.18 SD (range 2.23–2.79), mean low frequency 1.72 kHz ± 0.07 SD (range 1.64–1.87), mean frequency range 0.78 kHz ± 0.16 SD (range 0.57–1.11). At end of Song, Low Whistle may intergrade into Whine (Figure 4C, last element).

Song. Typically includes series of introductory Low Whistles, followed by series of Complex Whistles, then closes with Low Whistles and/or, less frequently, Whines (Figure 4C). Song includes a distinctive Complex Whistle transitional between introductory Low Whistles and typical Complex Whistles (compare first and second Complex Whistles in Figure 4C). Transitional whistle characterized by asymptotic rise in frequency following initial (i.e., descending) portamento and preceding first frequency spike. Asymptotic rise has mean duration of 255 ms ± 119 SD (range 121–410, n = 7) and mean frequency range of 0.73 kHz ± 0.18 SD (range 0.47–1.01, n = 7).

Following from sample of 50 songs recorded from ≥10 birds in Nulato Hills (n < 50 reflects incomplete or inadequate recording of song element). Mean number introductory Low Whistles 2.28 ± 1.53 SD (range 0–7, n = 46), mean number Complex Whistles 6.26 ± 3.69 (range 2–21), mean number closing Low Whistles 1.51 ± 1.06 SD (range 0–4, n = 47). Mean number of primary peaks/Complex Whistle/song 2.35 ± 0.62 SD (range 1.0–3.8, n = 49; maximum number primary peaks in any single Complex Whistle = 5). Because of variation in number of Low Whistles and Complex Whistles, Song duration quite variable; from Nulato Hills, mean Song duration 8.77 s ± 3.22 SD (range 5.24–19.09, n = 21). Significance of such variation unknown.

Within Songs, often multiple patterns of sequential frequency gradation. In Low Whistles, changes in initial, base, and closing frequencies may be sequentially graded (usually increasing during introductory whistles and decreasing during closing whistles for all 3 patterns); these patterns frequently correlated with one another (e.g., initial, base, and closing frequencies may increase across series of Low Whistles). Even when correlated, frequency range over which changes occur may vary (e.g., in a series of introductory Low Whistles, terminal frequency of successive whistles usually rises farther and at a faster rate than similarly graded initial frequency). Among successive Complex Whistles within single Song, peak frequencies of both primary and secondary frequency spikes may be sequentially graded. Portions of Songs typically characterized by pure whistles occasionally exhibit small-scale, rhythmic frequency modulation; such atypical frequency modulations produce quavering whistles that may occur in base frequency portions of Low Whistles (either introductory or closing) or across the asymptotic rise in the transitional Complex Whistle. As with variation in number of elements within and among Songs, significance of variation in frequency patterns needs study.

Shrill Whistle. Harsh, screaming whistle; may have almost gull-like quality. Frequency and temporal characteristics need study. Shrill Whistle depicted in Figure 4D (final call) 0.4 s at 2.50–3.00 kHz; ≥1 harmonic overtone. Amplitude high and constant for almost entire duration of call (i.e., rapid rise to and fall from peak frequency at start and end of call, respectively). Occasionally, Shrill Whistles transition rapidly from Chiu-eet s (as in Figure 4D).

Growl. Harsh snarl dominated by broad-band noise. As with Shrill Whistle, Growl may be derived from Chiu-eet . When so derived, call differs from typical Chiu-eet in 2 respects: (1) Chiu- eet portion of Growl bracketed by nearly vertical frequency rise and fall at very start and end, respectively (brackets continuous with and do not exceed in frequency readily identifiable start and end of Chiu-eet portion); and (2) Chiu-eet clearest during first half; broad-band noise predominates later in call (e.g., 5 of 6 Growls described below ended in broad-band noise). From series of 6 consecutive Growls (by same bird) where broad-band noise superimposed on discernible Chiu-eet, mean duration 373 ms ± 29 SD (range 327–397), mean total duration of broad-band noise 227 ms ± 70 SD (range 132–327), mean portion of call duration consisting of broad-band noise 60% ± 16 SD (range 38–84), and mean number of broad-band portions/call 1.83 ± 0.75 SD (range 1–3).

Other Calls. Less common and/or less well-documented calls: (1) Curlew Call—includes diversity of calls, usually of low amplitude, frequently given by paired birds in close proximity and rendered phonetically as curlew, curleeoo, and purr. . . purr . . . purr; (2) Brooding Call—used when calling to nearby chicks; (3) Copulation Calls—variety of poorly documented calls; includes derivatives of other calls (e.g., hoarse curlew calls, gurgling Whines, soft and/or warbling Complex Whistles) and calls heard in no other context, such as soft whistles and calls comprised of 2–5 elements characterized by sharp frequency breaks (similar to butterfly-flight call of American Golden-Plover [Pluvialis dominica]; Fig. 5 in Connors et al. 1993); and (4) Nonbreeding calls—e.g., on wintering grounds, curlews give soft twee or klee calls while walking or standing, typically when not interacting with conspecifics (JSM, REG); also give klee calls during migratory departures in spring (see Distribution and Habitat: Migratory Behavior, above). Klee calls may be variation of Shrill Whistle (BJM). Other vocalization known only from nonbreeding grounds, a repeated, whistled cheu-tu-tu similar to shortened version of Complex Whistle, apparently given only during agonistic interactions; e.g., by curlews in crouched, arched-back, dropped-wing posture during and shortly after birds run toward each other (JSM, REG). Context, range of variation, and significance of variation in these calls need study.

Phenology

Most vocalizations heard throughout year. Chiu-eet most common call throughout annual cycle. Low, Complex, and Shrill whistles, as well as Whines and Growls, given on and away from breeding grounds, relative importance in vocal array varies seasonally. For example, Low Whistles common as introduction to breeding Songs, but rare on staging grounds, usually from flocked birds; Whines common from courting and paired birds generally prior to incubation, and also among flock mates throughout breeding and fall staging period. Some vocalizations season-specific. Songs limited to breeding season; used from first day of arrival through brood-rearing, but less frequently as season progresses (BJM, REG, TLT). Nonbreeding calls (see above) known only from boreal winter (JSM, REG, BJM).

Daily Pattern Of Vocalizing

All call types and Songs heard throughout 24-h period on breeding grounds; breeding phase and context, rather than time of day, appear most important determinants of types of vocalizations given (BJM, REG, TLT).

Places Of Vocalizing

All major call types as well as Songs given in air and from ground. Relative frequency of air versus ground variable; most strongly skewed for Shrill Whistles (usually in flight) and Whines (primarily from ground). Exception to latter are Whines by flocked birds both from ground and air. Growls most often from flying birds on breeding grounds and roosting birds on staging grounds; also given year-round by birds in hand immediately following capture.

Repertoire And Delivery Of Songs

No information. Songs of any individual may be variable (e.g., variation in number and structure of Low and Complex whistles), but not known if variation continuous or organized into recognizable classes (BJM); needs study.

Social Context And Presumed Functions

Most given in wide range of contexts. Not known how variation within vocalizations corresponds to variation in context.

Chiu-eet. Given year-round by flocked and solo birds; delivered in wide range of contexts from ground and air. Most common vocalization in response to predators; call rate, amplitude, and frequency may increase as predator approaches. Usually first vocalization after flushing from nest (see Behavior: Predation, below). Given by territorial birds responding to presence and/or vocalizations of neighbors and transients; often given during intraspecific chases. In intersexual contexts, by nest-building male, by female approaching Scraping male, by male after landing with waving wings while courting unpaired female, and as contact call between paired birds (BJM, REG, TLT). Curlews readily respond to human imitation of Chiu-eet.

Low Whistle. Given most frequently in series as introduction to Song by males and females. Less frequently by males in series from air and ground without other vocalizations. Such series may lack portamento (and thus resemble Whimbrel's Low Whistle) during Undulating Flight Display (see Behavior: Sexual Behavior, below) and when returning from chasing intruder or predator off territory or away from brood. May lead directly into series of Whines; occasionally given softly by male when near mate on territory (BJM, REG, TLT).

Complex Whistle. Given in Song in multiple contexts (see below); occasionally given at end of Song (after landing with wings waving) without closing Low Whistles. Complex Whistle given alone as contact call between mates (particularly when predator or human passes through territory), by Scraping male, by female approaching male in nest scrape, and while Tossing at nest with incomplete clutch. Also, when young threatened by predator and when stooped upon by other attack-mobbing species (BJM, REG, TLT). On wintering grounds, used during intraspecific aggressive interactions (JSM, BJM).

Whine. Primary vocalization accompanying ground displays by males on territory. Given as announcement call from hummocks (particularly prior to pairing), and most common vocalization during Scraping display; may engage in Whining “duels” with neighbors. Occasionally given at end of Song (both sexes); for males in Territorial Flight Display (see Behavior: Spacing, below), most frequently during, or just after, landing. Whines may follow Complex Whistles, closing Low Whistles, or form hybrids with closing Low Whistles (BJM). Male also Whines after displacing rivals, when territory invaded by neighboring conspecifics tending broods, and in response to human imitation. Female Whines when visiting male territory prior to pairing, when approaching Scraping male, and as contact call with mate. Fledglings in brood aggregations Whine back and forth to each other and in response to Chiu-eets of parents. Off-duty breeding adults in communal flocks Whine as they forage, when returning to flock after tracking aerial predator, or as they arrive/depart communal areas (TLT, REG, BJM, JSM).

Song. Typically given by males in Territorial Flight Display, but also in many other contexts. Regularly given in response to songs of neighbors and in presence of transients flying through territories, particularly by males (from ground or after launching flight display); also by male returning to territories after driving off predators or rivals, and during agonistic intraspecific ground interaction. May be given softly by male during Pointing display once female enters nest scrape. Given by females in several contexts, including when on male territory while prospecting for mates, when male Whining from nest scrape, and when with male in Courtship Flight (see Behavior: Sexual Behavior, below). Once pairing occurs, regularly given as contact vocalization between mates foraging out of sight of each other, and when flying short distances together within territory. Female frequently initiates such singing when they fly together; sometimes only female sings. Both sexes also sing prior to nest exchanges. Atypically, Song and/or Shrill Whistle (see below) used by female “patrolling” over her territory. Song also used occasionally by parents in vicinity of nest or young in response to passing raptors, after being flushed from nest, and when returning to nest after bout of distraction display; common from adults in brood aggregations (BJM, REG, TLT).

Shrill Whistle. Given by adults near nest or young when latter threatened by predator. Chiu-eet s typical alarm call when predator initially approaches nest or young, but Shrill Whistles become more frequent, and may dominate vocalizations, once predator in close proximity to eggs or brood. When attack-mobbing, particularly near hatching and during brood-rearing, Shrill Whistle may be dominant vocalization (e.g., typically gives Shrill Whistle when diving at humans near its brood, frequently just as curlew flares at >1 m). Shrill Whistles may be given by members of territorial pairs in response to nest/egg predators even before nesting; occasionally by breeding birds when feeding off-territory in presence of potential predator and rarely, by either sex during early courtship. Shrill Whistles usually given in flight, but occasionally from ground, e.g., during bouts of Injury-feigning (BJM, REG, TLT).

Growl. During breeding, most typically given in flight by territorial males driving off intruding conspecifics, but many such chases lack Growls. When used in chases, may be accompanied by, or completely replace, Chiu-eet s. Less frequently, incubating adults Growl when approaching intruder after initial silent flush from nest, when attack-mobbing avian predators, and when captured by humans. Growls by off-duty breeders in communal flocks first heard in late Jun, just prior to hatching. Curlews also growl when attacked by other breeding birds (e.g., Long-tailed Jaegers [Stercorarius longicaudus]), after flushing in response to potential aerial predator, and as conspecifics land in midst of feeding flock. In fall, staging birds Growl when conspecifics arrive at tightly packed communal roosts (TLT, REG).

Nonvocal Sounds

None known.

Bristle-thighed Curlew Figure 4. Vocalizations of Bristle-thighed Curlews.
Enlarge
Figure 4. Vocalizations of Bristle-thighed Curlews.

Vocalizations of Bristle-thighed Curlews. A. Chick’s Whee call between 2 adult Chiu-eets, with sound spectrogram above and oscillo-gram below (Andreafsky Wilderness, AK, 5 Jul 1986, BJM). B. Adult Chiu-eets; male calls 1, 5, and 7; female calls 2–4, 6, and 8–9; note overlap between first male (faint) and female calls (recording details as in A). C. Song, with 5 elements including 2 introductory Low Whistles, a tran-sitional Complex Whistle (with asymptotic rise in frequency after initial descending portamento), a typical Complex Whistle, and a terminal Low Whistle grading into a Whine (Andreafsky Wilderness, AK, 9 May 1990, BJM). D. Alarm call series with Chiu-eet (first call) grading into Shrill Whistle (third call), with sound spectrogram above and oscillogram below; note second call intermediate in both frequency and amplitude pattern (recording details as in A). Prepared by E. H. Miller, Memorial University of Newfoundland, using Kay Elemetrics CSL 4100 (with effec-tive frequency resolution of 161.5 Hz and a 256-point FFT transform size).

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