Sounds

No detailed studies, except that Veen (1987) analyzed structures and motivations of 3 types of call. This account drawn largely from Cramp 1985, with un-published observations of the author. For contexts of calls, see Behavior: agonistic and sexual behavior, below. For sound spectrograms of common calls, see Cramp 1985, Veen 1987 .

Development

Chicks peep in egg from about 24 h before hatching. During first 2–3 d, chicks give soft peep call as they peck parents bill, developing into squeaky cheeping at ages 3–6 d. Distress Call (e.g., when unattended at night) penetrating zeee . Chicks >6 d old give persistent Begging Call kri-kri-kri-kri-kri . Begging continues as fledglings accompany parents for 2–3 mo post-fledging, especially when parent catches fish. Older fledglings give grating krrri, equivalent to adults kip call.

Vocal Array

Vocabulary large and varied. All calls have distinctive sharp, irritable timbre; lower pitched and harsher than corresponding calls of Arctic Tern.

Kip Call is a sharp kip given in a variety of social situations, including flock-feeding, where it probably expresses low-level aggression to nearby birds, during ascent stage of High Flight, or by adult accompanying fledgling. Similar call used in take-off from territory or from resting flock, or at landing in nest territory,

Advertising Call (Long Call of Veen 1987) is down-slurred keeur or keeuri (up-slurred at end); sometimes prolonged into series keeur-keeuri-keeuri-keeuri-keeuri . Given when approaching colony or nest-site, especially when carrying fish; also in High Flight and sometimes in territorial defense. This call varies among individuals and is probably used for recognition (Stevenson et al. 1970): chicks emerge from hiding-places and beg when their own parent approaches.

High-Intensity Alarm is harsh, shrill kee-arr or keeee-aarr; emphasis usually on first syllable but sometimes on second; occasionally single keeerr . Given from high overhead when human enters colony; also in antagonistic encounters with other terns, e.g., in High Intensity Threat displays.

Fear Call is loud, musical, descending kyew, given when surprised by intruder or attack by conspecific.

Kyaar Call is harsh, descending kyaar, given by one or both birds during ascent stage of High Flight or at Pass.

Attack Call (Rattle and Growl of Veen 1987) is staccato kek-kek-kek-kek, given in confrontations and fights; also when attacking human intruder, commonly ending in loud kyaaarr as bird strikes intruder and swoops up.

Korr Call is low-pitched korr-korr-korr or keeurr-krorr-krorr-krorr, commonly given in Bent Posture (e.g., when intruder approaches standing adult in nest territory or feeding territory); also given in High Flights.

Broody Call is low, crooning, krrr-krrr-krrr-krrr, usually given when scraping, turning eggs during incubation, or brooding chicks.

Begging Call is shrill ki-ki-ki-ki-ki, given by female soliciting food from mate (or, occasionally, other males); like chick’s begging call but less grating. Also given at low intensity by female in pre-copulatory display, usually reflecting submission or willingness to copulate. Occasionally given by either sex at low intensity in other situations involving close approach (e.g., during nest reliefs), probably signaling appeasement.

Copulation Call is quiet, squeaky kyi-kyi-kyi-kyi, given by male during pre-copulatory display and while mounted.

Several other calls described (e.g., Marples and Marples 1934, Palmer 1941, Glutz von Blotzheim and Bauer 1982, Cramp 1985, Veen 1987), but homologies, contexts, and functions are unclear and require systematic study.

Sexual Differences

Copulation Call given by male; Begging Call usually by female; no others reported.

Geographic Variation

No information.

None reported.