Sounds

Highly vocal, particularly on breeding grounds, where males and females share most of repertoire. Numerous vocalizations described by Bergman (1953, 1956); summarized below from Cramp 1985, except where noted.

Development

Young birds begin vocalizing while still in egg; respond to Fish Call (see below) with weak Begging Call, and react to Alarm Call (see below). Newly hatched young (3–6 h old) produce ee, ee, ee or i-i-i sound before feeding. Use this vocalization when pecking at adult’s bill to solicit food. Young beg with a vibrating, high-pitched whistling note i-i-i-i- (as in “see”) of varying length. Older chicks express hunger by vui or vi, which grows stronger and changes to ivi close to fledging; after fledging, begging call becomes more protracted and penetrating, uivi or uivii . Aggressive calls, identical to begging calls, are extremely common during first 3 wk. When able to fly and independent of territory, Contact Call (see below) develops. All calls become much stronger with development of flight. Weeeee (Whistle) heard when offspring accompany parents in flight or on ground (Fig. 2B).

Vocal Array

Calls only, given in various contexts.

Contact Call. Loud, relatively protracted rau or rrau; most common vocalization heard in undisturbed colony. Heard from mates at nest or from bird with brood.

Alarm Call. Figure 2A . Loud, barking ra, ra, ra, raeu, rra . Commonly given when intruder approaches colony; also during High Flight (see Behavior: sexual behavior, below).

Gakkering Call. Vehement, rasping ra ra ra-ra-rarau; disyllabic final note observed in ca ca ca crau-au (Miller 1943); comprises elements of Alarm Call run together to produce sequence of increasing frequency, ending in note louder and more extended than Alarm Call at closest point to intruder during air-to-ground or aerial swoop.

Fish (Advertising) Call. A 4- to 5-note ra-ra-ra-ratschrau; probably facilitates individual recognition (mate–mate, parent–offspring). Uttered throughout breeding period and delivered mostly in flight, especially by male arriving with fish for female. As tern calls, performs series of expressive movements in flight, referred to as Fish-Bending or Fish-Bowing: First contracts neck, then stretches head forward and downward, uttering first rra of call; then quickly raises head and bill diagonally, almost straight upward; simultaneously raises tail and utters last syllables of call, with emphasis on last syllable, then assumes normal posture. Also performs this movement on the ground, often with fish in bill. Call usually given 2–5 times at about 5-s intervals, or by both sexes when they have young. Also given on ground to summon young from hiding or danger; sometimes preceded by Alarm Call.

Female Begging Call. Soft begging rea rea rea or graa, graa; high, weak, reedy reee or raa; used to sol-icit courtship-feeding and copulation from male.

Other Sounds. Birds often produce aggressive vocalizations when fighting and rushing each other. Short hard aeh, aeh . . . or kraeh, kraeh . . . uttered in quick succession; may turn into hard, whirring rro-rro-rra-rrerrerre . In courtship flights, occasionally utters calls such as rrou, rrou .

During High Flight in courtship (see Behavior: sexual behavior, below), birds produce a nonvocal sound with wings while in steep glides. Sound similar to nonvocal sound made by Common Nighthawk (Chordeiles minor) in dive, a soft, descending buzz (FJC).