Inca Tern Larosterna inca Scientific name definitions

The Inca is the most aberrant member of its family and is placed in its own monotypic genus. Its body is charcoal grey, with dark black primaries and black cap, and bright red bill and legs. The most distinctive feature of this species are its prominent white moustaches which, starting at the base of the bill, are quite long and curl down around the cheek. The Inca Tern is primarily coastal occurring from north central Chile to Ecuador. It is quite common along near shore waters where it forages for anchovetta but are most easily found along rocky coasts where they breed on sea cliffs and guano islands. Though highly distinctive at close range, from a distance, this species can easily be confused with the Grey Gull, especially juveniles, but note structure and especially on the adult, the bright red bill.

39–42 cm; 180–210 g (in captivity, average 189 g). Unique and unmistakable; body dark slate, paler on throat and underwing-coverts ; white stripe curling back and downwards from gape to side of neck, where it fans out into long satiny feathers; trailing edge of wing white, and white edges to four outer primaries; iris brown, bill and legs dark red; yellow bare area or wattles at base of bill; wing shape rounded, and tail moderately forked; has characteristic fluttering flight, with rapid wingbeats; serrated flange on middle toe unique among terns. Juvenile uniform blackish, with small grey tufts at base of bill. Subadult has brown cast, and dark horn-coloured bill which reddens with age; curling gape plumes dull brownish.

Humboldt Current region from N Peru (Lobos de Tierra I) S to C Chile (at least to R Aconcagua, Concon Is (1 Simeone, A., Luna-Jorquera, G., Bernal, M., Garthe, S., Sepúlveda, F., Villablanca, R., Ellenberg, U., Contreras, M., Muñoz, J. and Ponce, T. (2003). Breeding distribution and abundance of seabirds on islands off northcentral Chile. Rev. Chilena Hist. Nat. 76(2): 323–333. Close ) ).

Mainly found on inshore “guano islands”, but also 67 km offshore on Hormigas de Afuera I; typically along rocky coasts, or where sandy beaches are backed by cliffs. Nests on rocky sea cliffs and guano islands, also in artificial structures .

Permanently resident, with no systematic migration. Non-breeders move opportunistically to follow food. Some disperse N to Ecuador. Recorded as vagrant from Costa Rica (2 Obando-Calderón, G., P. Camacho-Varela, J. Chaves-Campos, R. Garrigues, M. Montoya, O. Ramírez-Alán, and J. Zook (2014). Lista oficial de las aves de Costa Rica. Actualización 2014. Zeledonia 18(2):33–50. Close ) and Panama.

Mainly small anchovetta (Engraulis ringens); also planktonic crustaceans; offal and scraps. Associates with fishing boats; large flocks (average 100+ in C Peru) attend fishing activities, including dynamiting. Rapidly detects a surfacing sea lion, and is the most numerous species associating with these mammals. Feeding flocks number up to 5000. Forages mainly by plunge-diving, and contact- and surface-dipping; scavenges for scraps left by sea lions and avian predators.

Probably aseasonal. Eggs found Apr–Jul and Oct–Dec; young found mid-Jul. In the north of the range, on the Lobos de Afuera islands off N Peru, chicks, juveniles and displaying adults have been found in November and courting, mating and incubating birds in August (3 Figueroa, J., and M. Stucchi (2008) Las aves de las Islas Lobos de Afuera (Perú) en la primavera de 2004. Ornitología Neotropical 19: 377–390. Close ). Nests in fissures, burrows and small caves, in troughs in guano or sand, and at base of or under rocks and boulders on island slopes; in abandoned petrel burrows or at entrance of penguin burrows; also on ledges in and under buildings and piers. Many nest on abandoned dredges and barges in harbours. Often with Peruvian Diving-petrel (Pelecanoides garnotii) or Red-legged Cormorant (Phalacrocorax gaimardi). Where vultures present, nests more hidden; sometimes forced to abandon breeding attempt when other seabirds begin nesting.

Clutch size is 2 eggs, sometimes 1, usually well hidden in tunnel or crevice; incubation period not reported; chick dark grey above , paler grey below, with faint speckling on head; fledging c. 4 weeks; fully dependent for at least 1 month further, during which practises foraging techniques. This species is monogamous and both sexes incubate and provision the young. The distinctive head ornaments; the long white moustache plumes and fleshy yellow wattles, are similar in both sexes and have a role in mutual signalling of body condition, and prediction of reproductive performance and chick quality, moustache length being  the most reliable signal in both sexes (4 Velando, A., Lessells, C. M. and Márquez, J. C. (2001). The function of female and male ornaments in the Inca Tern: evidence for links between ornament expression and both adult condition and reproductive performance. Journal Avian 32: 311–318. Close ).

Not globally threatened. Currently considered Near Threatened. Numbers fluctuate from year to year, depending on food availability in relation to El Niño; populations decline greatly during severe occurrences of El Niño, but rebound quickly, suggesting mass emigration rather than mass starvation; total population estimated to vary around c. 50,000 pairs. In 2011 estimated to total around 150,000 individuals (5 Wetlands International (2015). Waterbird Population Estimates. Wetlands International, Wageningen, The Netherlands. Close ). Main abundance on C coast of Peru among inshore guano islands, particularly Chinchas, Pescadores and Asia Is. Formerly considered present in enormous numbers, but neither as abundant, nor as vulnerable, as the typical guano species. Main nesting habitat is not limited. Formerly confined to coastal Peru; first bred in Chile during late 1930s and is now common S to Valparaíso.