Sounds

Information on Eastern Willet from Douglas 1996, unless referenced otherwise.

Development

Soon after hatching, first vocalization is high pitched “ eeee ” serving as distress call. At age 5 wk, vocalization “ phwee-hoo ” given frequently just prior to acquiring flight capability (Hansen 1979); this call probably same as “ kyah-yah ” (Sordahl 1979) and associated with flight enticement and appeasement.

Vocal Array

Moderately complex commun-ication system utilizing both discrete and graded vocalizations; 9 vocalizations common in both subspecies, several intermediates of these vocal forms, and 6 other rare vocalizations (fluted whistle, croak, growl, stutter, gleep) described for adult Eastern Willets (Douglas 1996). One rare vocalization, “whistle,” described for juvenile Western Willets (Sordahl 1979) not reported for Eastern Willets. Graded transitions between common vocalizations occur coincidentally with shifts in motivational states. Intermediate forms of common vocalizations employed in special contexts; e.g., with broods. “Note” defined as continuous tracing on sonogram (Nelson and Marler 1990); “syllable” represents aurally distinct component of call; “song units” or “call units” recognized as discrete, repeating structures for which within-unit intervals always significantly shorter than between-unit intervals (Isaac and Marler 1963); “interval” refers to cessation of sound between signal elements; “sequences” are strings of similar units; “phrases” are combinations of dissimilar call units; “variant” is distinct variation of vocalization; “duration” is length of time over which vocalization is audible; and “form” is inclusive term including phrases, transitions, graded series, and intermediates.

PWW (Pill-Will-Willet) Call. Figure 2A, 2B . Three variants of PWW Calls may occur in association with agonistic behavior and alarms. Call comprised of 3 distinct syllable types: pill, will, and willet . These repetitive stereotyped song units (often >200/flight display) begin with strongly pulsed amplitude modulations in first syllable type (pill; repeated mean 3.1 times ± 0.46 SD; range 3–5, n = 123 PWW Calls) and shift to frequency modulation in latter 2 syllables (will with 1 hump-shaped frequency modulation and willet with 2 hump-shaped frequency modulations). First pill note of PWW Call has highest amplitude and also most harmonics (mean 4.4 harmonics ± 1.3 SD; n = 57). Fundamental frequency and odd harmonics usually suppressed in will and willet . Sound energy concentrated in second harmonic. Occasionally sound energy dis-placed upwards from second harmonic to higher harmonic or single harmonic may degrade into broad-band lower and upper formants. These characteristics found in 3 variants of male PWW Call. Shifts in concentration of sound energy may occur coincident with changes in behavioral states and often followed by transitions into other call types. Female song in Eastern Willets (and presumably in Western Willets) lower in frequency, less tonal, and less modulated in frequency. By comparison, female song sounds less musical and flatter than that of male. Males augment flight song with wing displays that alternate between fixed and oscillatory modes, prominently exhibiting conspicuous white wing-stripe. Acoustical and optical displays not coupled. Repetition of song units continues unbroken in flight display, and interval between song units highly uniform within individuals (mean 0.23 s ± 0.37 SD; n = 204 intervals for 1 individual) and between individuals (mean 0.16 s ± 0.05 SD; n = 102 individuals). Male PWW Call audible up to 700 m away, depending upon topography, atmospheric conditions, and altitude of broadcast.

Kyah-yah. Figure 2C . Kyah-yah used as appease-ment when crossing territories, flight enticement preceding flight, and as contact call within groups when flying from foraging areas to breeding areas; also used in migration; given in response to Scream Calls by Willets joining predator mobbing event; also given by Willets after successfully repelling predators from nesting territory. Variants, ranging from 1 to 7 syllables, uttered in strings or with other calls. Syllables begin with sharp frequency upsweep, followed by broad midsection, and ending in sharp frequency downsweep. Up to 8 harmonics can be seen in sonogram (depending on sensitivity setting) with maximum harmonic frequency of 14.6 kHz. Second harmonic often emphasized; fundamental usually weaker. Variable in frequency modulation, duration and intervals, distribution of spectral energies between harmonics, and tempo and number of call units in sequence or phrase. Very short notes may ornament beginning or end of syllables. Shift in emphasis upwards to higher harmonics often precedes or accompanies change in behavior and transition to other calls.

Kleep. Five to 12 harmonics; maximum harmonic frequency 16.8 kHz. Fundamental frequency often weak or hidden. Duration to interval ratio appears to vary systematically and recognized as measure of intensity (Sordahl 1979). Relative length and shape of notes changes with intensity ranges. Duration increases with increasing intensity and ap-pears related to motivational state of signaler. At very low intensity, Kleep Calls are single staccato notes, unvariable in frequency. Low-intensity Kleep most commonly consists of apostrophe-shaped note, increasing sharply in frequency, followed by pennant-shaped note that decreases less sharply in frequency, and separated by very brief break in sound energy. Videotape analysis revealed that signal frequency in Kleep positively correlated with changes in angle of beak opening. Signal frequency (kHz) increased as beak opened wider, and decreased as bill closed. Relative distribution of sound energy across harmonics varies and may be related to motivational state.

Klik. Sequence of similar double-noted calls, resembling low-intensity Kleep, but uttered at more rapid tempo. First note increases sharply in frequency, second note decreases sharply in frequency and very brief interval separates the 2. Second har-monic consistently emphasized and first harmonic sometimes hidden. Maximum of 6 harmonics and some 3- and 4-note calls occurred in agonistic interactions. Tempo, duration, and duration/interval ratios more variable in agonistic interactions, while in courtship these parameters tended to be uniform and ritualized. Tempo increased in agonistic encounters as display progressed and distance between aggressor and opponent decreased.

Dik. Repetitive, single-note call with harmonic structure, short duration, rapid onset, and little or no frequency modulation. Sound intensity generally concentrated in lower harmonics than is true for Kleep . Uttered by female at tempo approximately half rate of Klik during courtship. Emphasized frequencies of these 2 calls are similar but not the same, and Sordahl (1979) noted that this created sensation-like acoustic beats.

Cluck. Soft and inaudible at distances >30 m. Appears to be random jumble of low staccato notes in various conformations. Emphasized frequency, note duration, and tempo of Cluck Calls probably related to intensity of display.

Hunker-hunk. Some elements of call appear homologous with PWW Call, suggesting this call as subdued form of PWW Call.

Scream. Relatively high-pitched, graded vocal form variable in duration, amplitude modulation, frequency modulation, and number of syllables. In Eastern Willet, mean emphasized frequency of Scream calls ranged from 2.4 kHz to 3.0 kHz, with the highest harmonic at 7.9 kHz. Amplitude and frequency modulation may occur simultaneously or independently and increase or decrease within single-call unit. Scream Calls sometimes given in multisyllabic forms similar to Kyah . Duration in Eastern Willet ranges from 0.10 to 0.93 s. Within call, duration of elements typically increase or decrease, suggesting that rate of amplitude modu-lation is related to levels of motivation. Up to 6 harmonics may be present, but normally only 3 apparent. Fundamental frequency suppressed, and second, fourth, and sixth harmonics emphasized, while odd harmonics weak. Highest recorded harmonic frequency 7.9 kHz. Scream Calls distinguished as having relatively long (Scream Attack) or short (Scream Flee; Sordahl 1979) durations.

Geographic Variation

Eastern and Western willets share vocal repertoire. Between subspecies, PWW Call of males differs statistically in both acoustical frequency and temporal characteristics (Douglas 1996). Eastern Willets discriminate between male songs of Eastern and Western willets (Douglas 1998). Vocal repertoire of Western Willets highly uniform within populations (Sordahl 1979), but 2 individuals from n. California had song dur-ations significantly longer than those recorded in Utah (Douglas 1996, Douglas and Conner 1999). This difference was greater than that found among Eastern Willets from Nova Scotia to Florida, where no geographic variation in vocalizations detected (Douglas 1996). More studies needed, especially for Western Willet.

Phenology

Willets relatively quiet during nonbreeding season, quieter than other shorebirds; even alarm calls and contact calls at roost less fre-quent (Douglas 1996). PWW Call rarely heard in winter but can be provoked by tape playbacks (McNeil and Rompré 1995). Some Western Willets begin uttering PWW Calls on wintering grounds in San Francisco Bay, CA, just prior to departing northward (H. Cogswell pers. comm.).

Daily Pattern

During breeding season, daily bouts of PWW Calls most intense in early morning and evening; countersinging may occur between competing males at any hour of day or night, on both nesting territories and foraging areas. Frequencies of PWW Calls and display flights sharply reduced at start of egg-laying and during incubation. After eggs hatch, intense vocalizing (Scream, Kleep) and antipredator displays become more frequent as frequency of PWW Calls and flight dis-play continue to decline, ceasing completely by time adults abandon young.

During brood-rearing, some adults regularly assume high perch on tip of tall conifer approximately 1 h prior to sunset and vocalize incessantly (Kleep) for up to 1 h without pause, though intensity may vary between low and high repetition rates. During these vocal displays, other Willets can be heard giving similar displays, almost like a chorus. After sunset, adult glides from its perch to ground and presumed brood center; activity of adults and chicks and vocalizations cease. This daily pattern of behavior is in marked contrast to pattern during prenesting period, when vocalizations may be heard at any hour of day or night.

Places Of Vocalizing

See Figure 3 . Male Eastern Willets frequently vocalize in aerial displays over nesting, foraging, and chick-rearing territories. Willets scold intruders from perches on bushes, trees, fences, posts, rocks, buildings, and utility poles (Bent 1929, HDD). In the Chebogue River Estuary, Yarmouth Co., Nova Scotia, males utilize low hummocks on their territories for countersinging when neighboring males perform flight displays (HDD). During brood-rearing, adult uses tips of highest conifers like sentry posts from which to vocalize about potential threats. These sentry signals relayed by adult on ground, and chicks respond predictably, either foraging or hiding, in response to temporal and frequency characteristics of calls (Douglas 1996). Periodically adults exchange roles and positions; during such exchanges, they maintain contact vocally.

Repertoire And Delivery Of Songs

PWW Call functions similar to oscine song in that it is used in territory defense and/or self advertisement (Douglas 1996). This call highly uniform within in-dividuals and geographically. Largest number of song sequences measured in single aerial display >209 PWW Calls given in 162 s; calls within this series averaged 0.56 s ± 0.02 SD (n = 209) in duration, separated by mean interval of 0.23 s ± 0.04 SD (n = 204). Along coast from Nova Scotia to Florida, PWW Calls averaged 0.59 s ± 0.042 SD (n = 127); separated by intervals of 0.16 s ± 0.051 SD (n = 102). Largest number of female PWW Calls in single display >88, delivered from hummock in salt marsh, duration 107 s and highly uniform, as in male song. PWW Call duration averaged 0.6 s ± 0.06 SD (n = 88), and interval between calls averaged 0.3 s ± 0.3 SD (n = 83).

Social Context And Presumed Functions

See Vocal array, above.

None known.