Sounds

Development

First vocalizations, peeping sounds, produced when egg pips prior to hatching. These calls appear identical to Begging Calls produced by newly hatched chicks, which are presumed to elicit regurgitation of food from parents. As chicks grow, Begging Call changes. Small chicks simply sit or stand, and peep with head lifting slightly with each call. By 2–3 wk, chicks thrust head forward with mouth open during calling, which is now more intense. By 4–5 wk, chicks beg with head hunched against body, lifting head each time they emit high-pitched peep. Call appears identical to Begging Call in adults (see Vocal array below).

Another vocalization shown by chicks is Shrill Waver, given when chicks pursued or grabbed, either by predator, conspecific, or investigator. Virtually identical vocalization produced by adults in similar contexts. Tinbergen (1960) suggests that this call is similar to Alarm (gakkering, hahaha) Call produced by adults.

During 4-yr transition to adulthood, acquire remaining adult vocal repertoire, although in several cases age of acquisition and ontogeny of specific vocalization unknown. Three-year-old birds show Long-call Note (Keow or Yelp), Long Call (Trumpeting), and Warning Call (Plaintive Yeow) (Tinbergen 1960). Two-year-olds not observed to show these calls (RJP). Calls specifically associated with mating and chick-rearing (Mew Call, Choking, Copulation) only observed in breeding (4- to 5-yr-old) birds.

Vocal Array

No “song,” but species has complex repertoire of at least 8 (Tinbergen 1960), possibly 12–15, calls. Two of these used by prefledged chicks, 3 others exclusively by adults during breeding (Mew Call, Choking, Copulation). Calls influenced by body posture. Behavior associated with calls described under Behavior. Description of calls follows Moynihan (1955, 1958) and Tinbergen (1959, 1960) except where noted.

Long Call. Figure 3A . Also called Trumpeting (Tinbergen 1960). Most elaborate and variable call in repertoire. Almost certainly functions in individual identification in many contexts, e.g., given by both members of pair when 1 returns after absence, first by returning bird, with mate typically responding before first bird has finished. Call consists of several repeated notes produced while bird lowers and then elevates head to Oblique Posture (see Behavior: Agonistic behavior, Communicative interactions; also see Fig. 4). First note(s) longer and lower, probably because of bend in neck and lowered head. Subsequent notes louder and higher pitched (more piercing), show little variation (within an individual) in fundamental frequency, duration, or relative distribution of energy within harmonics (Hand 1979). Final notes flatter and lower pitched, may change into a series of Yelps.

Long-Call Note. Also called Yelp or Keow. Low intensity, single-note version of Long Call. Highly variable among individuals, may function in individual identification. Often given when predator approaches; also by birds observing other birds fighting, and may function to indicate state of agitation. Heard all times of year, most often during breeding when many individuals are crowded together (Tinbergen 1960).

Warning Call. Also called Plaintive Yeow. Simple, clear, slightly descending call, given only by flying birds. Differs among individuals primarily in duration. Tinbergen (1960) considers this call very similar to Long-call Note. Apparent structural differences exist. Warning Call has longer note length, descends markedly in pitch. Difference in structure may result from way in which bird holds neck and head. Flying birds hold neck straight with head and bill in line with neck, in contrast to curve in neck with head perpendicular to neck in Long-call Note. Warning Call is call heard most frequently when visiting (and disturbing) breeding colony.

Mew Call. Figure 3B . Long-drawn, single note invariably linked with distinctive forward bent posture with neck stretched forward and arched. Occurs primarily in four contexts: (1) courtship and precopulation, (2) parent-offspring interactions, (3) nest relief, and (4) aggressive encounters between territorial birds and neighbors. In courtship given primarily by male after returning from absence when about to regurgitate food for mate-feeding; may serve to call mate to be fed. Parents carrying food also use Mew Call to attract offspring; call can be given with beakful of food. In nest relief, given by bird approaching nest, sometimes with nesting material in beak. In these cases appears to function as affiliative call, to get attention of mate or chick. In aggression, given by birds that appear highly agitated; can be last vocalization produced prior to attacking or being attacked.

Begging Call. Simple Klee-ew call, accompanied by Head-tossing in which bird assumes a hunched posture and flicks head up sharply while emitting call. Given by female in response to Mew Call by returned male, also given by both male and female prior to mounting. Call virtually identical to food-begging call of chicks (see above, Development) but has softer, less-demanding quality.

Copulation Call. Only call produced solely by males. Loud and regular in rhythm, staccato and guttural in quality, with energy concentrated in 1–2 heavy bands. Tinbergen (1960) describes call as more or less intermediate between Choking and Alarm Calls, but Hand (1979) shows low-intensity Copulation Calls not clearly distinguishable from Choking. Call produced by male after mounting, initiated during phase when tail is lowered and cloacal contact begins, continued until completion of copulation. Probably functions to advertise highly motivated state of male and to discourage interruptions.

Choking. Named after accompanying visual display (Moynihan 1958, Tinbergen 1959). Usually performed in tandem by mated pair. Birds squat, or crouch, with breasts lowered to ground and tails elevated. Call uttered as head and neck pump with hyoid bone lowered, producing huoh-huoh-huoh sound. Occurs in 3 contexts: (1) agonistic encounters, where territorial birds engage neighbors across shared boundary, (2) early stages of courtship, especially during nest-site choice, and (3) during nest exchanges. Appears to indicate tendency to remain in specific physical location (Hand 1979); may explain similarity to Copulation Call, with which males also indicate disinclination toward displacement.

Alarm Call. Figure 3C . Also called Eh-Eh, HaHaHa, or Kek-Kek Call. Given in response to predator (observer), especially on breeding colony (Tinbergen 1959, 1960). Given primarily when predator is first seen but does not pose immediate threat. If predator comes closer, birds shift to Yelping or take to air uttering Warning Calls. Call structure has wide frequency distribution with closely spaced harmonics. May indicate tendency to flee (Tinbergen 1959, 1960). Often alternates with Charge Call, so may also indicate conflict between flight and attack.

Charge Call. Given when diving at intruder or predator, or during aerial pursuit of conspecific or predator. Tinbergen (1960) regards this as modified Long-call Note; however, more similar structurally to Mew Call (Hand 1979) and may indicate high state of arousal.

Shrill Waver. As described for chicks (see Development, above), call given when bird is grabbed or attacked unexpectedly, either by predator or conspecific. Structurally related to Begging Call. Females grabbed by mate or male they are courting may Head-toss, give Shrill Waver, or combine the 2. Begging Call and Shrill Waver are first 2 vocalizations developed.

None described.