Peruvian Tern Sternula lorata Scientific name definitions

The Peruvian Tern is endemic to the Humboldt Current zone along the Pacific Coast of South America, from central Ecuador south to northern Chile. It is included in the cosmopolitan Sternula superspecies, of which two other representatives occur in the Neotropics, the boreal migrant Least Tern Sternula antillarum and Amazonian resident Yellow-billed Tern Sternula superciliaris, neither of which occur within the range of the Peruvian Tern. The Peruvian Tern nests well above the tide line on broad beaches or dunes but will also nest on barren stony desert a considerable distance inland. It feeds primarily on anchovetta although the diet also includes krill; Peruvian Terns capture their food by plunge-diving from heights of up to 10 m.

22–24 cm. Typical small tern: white forehead extending over eye, contrasting with black cap and lores; pale grey upperparts ; dark outer primaries; pale greyish white sides of neck and underparts; yellow bill tipped black, dark yellow legs. Non-breeding adult has crown streaked with white. Juvenile has broad dark brown face mask from lores to ear-coverts; buffy underparts; beige upperparts with bold black chevrons on lesser coverts, less pronounced on greater coverts; blackish primaries; dark-tipped yellowish bill and pinkish legs.

Humboldt Current zone from C Ecuador (Guayaquil) to N Chile (Antofagasta). Few confirmed breeding sites in Peru (Pacasmayo, Paraíso, Puerto Viejo, Pampa Lechuzas, Yanyarina) (1 Zavalaga, C.B., Plenge, M.A. and Bertolero, A. (2008). Nesting habitat and numbers of Peruvian Terns at five breeding sites in the central-southern coast of Peru. Orn. Neotrop. 19(4): 587–594. Close ) and Chile (Mejillones Peninsula and nearby areas) (2 Guerra, C. (2003). Nidificación del Gaviotín Chirrío, Sterna lorata en Bahía Mejillones del Sur: Mitigación y Manejo para la Protección de las Poblaciones Locales. Informe 2002, Año 1. Corporación Nacional del Cobre de Chile, CODELCO FUREME, Antofagasta, Chile. 75 pp. In Spanish. Close , 3 Guerra, C., Guerra, C., Moya, I. and Páez-Godoy, J. (2007). Plan de Recuperación, Manejo y Conservación para Gaviotín Chirrío (Chico) Sterna lorata en el Norte de Chile. Comisión Nacional de Energía. 37 pp. In Spanish. Close ).

Coastal. Breeds on broad sandy beaches and sand dunes, often more than 1000 m from tide-line; and on barren stony desert several kilometres inland. Shallow waters of estuaries and coastal lagoons appear to be important as foraging areas (4 Zavalaga, C.B., Hardesty, J., Mori, G.P., Chávez-Villavicencio, C. and Tello, A. (2009). Current status of Peruvian Terns Sternula lorata in Peru: threats, conservation and research priorities. Bird Conservation International. 19(2): 175–186. Close ).

Unknown, but returns to colony sites in mid-October. Post-breeding dispersal occurs from April until July, to unknown areas, probably offshore (5 Mackiernan, G., P. Lonsdale, N. Shany, B. Cooper, and P. Ginsburg (2001). Observations of seabirds in Peruvian and Chilean waters during the 1998 El Niño. Cotinga 15:88–94. Close ). Hundreds were sighted 25–200 km offshore during the 1997–1998 El Niño event, which indicates an ability for wide dispersal when conditions demand (1 Zavalaga, C.B., Plenge, M.A. and Bertolero, A. (2008). Nesting habitat and numbers of Peruvian Terns at five breeding sites in the central-southern coast of Peru. Orn. Neotrop. 19(4): 587–594. Close ). 

Mainly small fish  , particularly anchovetta (Engraulis ringens); 10% of diet reported by one study was krill (Euphausia). Feeding methods similar to those of allospecies. Prey remains found at nests have included Peruvian Silversides Odonthestes regia regia and Mote Sculpins Normanichthys crockeri (6 Zavalaga, C. B., M. A. Plenge, and A. Bertolero (2008). The Breeding Biology of the Peruvian Tern (Sternula lorata) in Peru. Waterbirds 31(4):550–560. Close ). 

The vernacular name in Chile, chirrio, is onomatopoeic. The frequent contact call is a short and sharp "chirrio, chirrio".

October–January (mainly November); full-grown juveniles in mid-February. Semi-colonial to solitary; nests more than 50 m apart in very sparse colonies of 2–15 pairs on back beaches and on desert plains. Scrape on unvegetated flats , usually near some object such as stone, shell, bone, stick. 1–2 eggs  ; incubation  22–23 days; chick pale grey, finely spotted black on head and back; hatching weight 6–7 g. Many eggs disappear; usually only 1 chick raised. May skip nesting in El Niño years. Nesting behaviour may be adapted to withstanding high rates of predation, notably by foxes (Pseudalopex spp.); a study in Peru found that egg-laying is asynchronous both within and between breeding groups, extending from mid October to late January; the low nest density (five to seven nests/km²), absence of nest material, camouflage of eggs and chicks, and high mobility of chicks few days after hatching are traits that may decrease nest detection by predators (6 Zavalaga, C. B., M. A. Plenge, and A. Bertolero (2008). The Breeding Biology of the Peruvian Tern (Sternula lorata) in Peru. Waterbirds 31(4):550–560. Close ). 

ENDANGERED. Previously considered not globally threatened. Status very poorly known; species probably rather rare. Estimated maximum population in Peru 5000 pairs but the global population may be no more than 1000–2500 individuals (7 Wetlands International (2015). Waterbird Population Estimates. Wetlands International, Wageningen, The Netherlands. Close ). Potential predators include Peregrine Falcon (Falco peregrinus), grey fox (Dusicyon culpaeus), and skunk (Conepaetus rex). Vulnerable to egg loss. Unattended nests may quickly be buried by sand. Current threats include recreational activities, off-road driving by fishermen and tourists, wetland pollution, conversion of desert plains to agricultural land, management of wetland water levels, presence of feral cats and dogs, and oil exploration on the desert plains (4 Zavalaga, C.B., Hardesty, J., Mori, G.P., Chávez-Villavicencio, C. and Tello, A. (2009). Current status of Peruvian Terns Sternula lorata in Peru: threats, conservation and research priorities. Bird Conservation International. 19(2): 175–186. Close ).The construction of a new seaport at Pampa Mejillones, Chile, is on the site of the principal colonies in Chile, which are accordingly threatened.