Peruvian tern

Sternula lorata is a tern of the family Laridae, described by Philippi and Landbeck in 1861 ^[1]. In Peru it is called «gaviotín peruano» ^[2]. It is a bird of the Humboldt Current that, unlike other seabirds, breeds in the coastal desert; at Paracas its nests lay between 1 and 3.7 km from the sea ^[3]. It nests on the coast of Peru and northern Chile ^[4], and Peru's official list of threatened wildlife approved in 2014 places it in the Endangered category ^[5].

It is among the smallest terns: about 23 cm in total length, with chicks reaching a top weight of about 50 g ^[4]. Its eggs, cream with dark brown spots, blend into the desert floor; at Paracas they averaged 31.84 mm in length and 23.88 mm in width ^[3]. Chicks up to one day old weighed 6.7 g on average and had beige down with black spots on the head, wings and back, white down on the breast and belly, and pink legs ^[3].

In the Paracas desert its nest is a plain hollow with no decoration, whereas that of the snowy plover (Charadrius alexandrinus), which breeds in the same area, tends to be lined with pebbles or shell fragments; the plover's eggs are also white with black markings ^[6].

Between 2003 and 2008 it was recorded at 14 localities on the Peruvian coast, from the San Pedro de Vice mangrove (5° 31′ S) to the Ite wetlands (17° 56′ S), a stretch of about 2200 km ^[4]. Wandering birds have been reported as far north as Salinas, in Ecuador, and its known southern limit is La Rinconada, in Chile, a few kilometres south of the Mejillones Peninsula ^[4].

Of those localities, 43 % were coastal wetlands, 36 % desert plains less than 2 km from the sea and 21 % open ocean, up to 45 km offshore ^[4]. At Paracas the nests lay on flat plains below 100 m in altitude, on coarse sand and salt crust with scattered stones; about 92 % of them were associated with stones, which help to shelter and camouflage the chicks ^[3].

In 2011 signs of breeding were found on three plains in La Libertad, Río Seco, Pacasmayo and Urricape, including a nest with 2 inactive eggs at Pampa Urricape ^[7]. In the south, at Pampa El Palo (Ilo, Moquegua), a new colony with a breeding area of about 600 ha was described, where between August 2016 and March 2017 12 active nests were found and from 8 to 324 birds were counted ^[8].

Egg-laying is not synchronised and runs from September or October to January or February; colonies usually hold fewer than 10 nests, and each pair lays 1 or 2 eggs, although generally only one chick fledges ^[4]. At Paracas, between November 2006 and July 2008, 60 nests were located: 59.6 % of clutches had 2 eggs, 36.2 % had one and 2.1 % had three ^[3].

In the 2006-2007 season at least one egg hatched in 55.6 % of the 27 nests followed ^[3]. Active nests were 44.18 m to 3.28 km apart, and the birds showed attachment to their breeding ground: 3 nests were used again that season and 7 in the next ^[3].

In September 2015 geolocators were fitted to 10 incubating adults at Mejillones, Chile, and 3 were recovered the following season ^[9]. All three birds stayed near Mejillones until 31 December 2015; from January to July 2016 they spent the non-breeding season at various points on the Peruvian coast, such as Paracas, the stretch between Eten and Paraíso or the San Pedro de Vice and Paita area, and perhaps in southern Ecuador, and in July 2016 they returned to Mejillones ^[9]. The data showed no second nesting away from Mejillones ^[9].

At 7 of the 15 colonies checked in northern Chile between 2008 and 2018, 146 fish were collected beside the nests; the commonest were Scomberesox saurus and Trachinotus paitensis, with 42 specimens each, and they measured 36 to 192 mm in standard length, 73 mm on average ^[10]. In 14 regurgitations from chicks Engraulis ringens predominated (35.7 %), followed by Sardinops sagax (21.4 %), and small squid also turned up; one adult regurgitated the remains of 8 euphausiids of the genus Euphausia ^[10].

Its main predators are foxes of the genus Pseudalopex and gulls of the genus Larus ^[4]. At Paracas the birds were most active between 6:00 and 9:00 and then all but vanished from the desert; the peregrine falcon (Falco peregrinus), the variable hawk (Buteo polyosoma) and the turkey vulture (Cathartes aura) were also seen there, but only one failed hawk attack and one nest with fox tracks were documented ^[6].

In Peru it is classified as Endangered ^[5]. The 283 birds recorded between 2003 and 2008 at 14 localities were counted over a surveyed area of some 1388 ha, just 0.35 % of the area suitable for nesting along the Peruvian coast, so that figure probably falls short ^[4]. On the Paracas Peninsula up to 605 birds were counted in May 2007, 550 adults and 55 juveniles, and 37 nests in the 2006-2007 season, figures that exceed those reported for other localities ^[6].

The threats identified in Peru are recreational use of beaches, cars driven off the tracks, pollution of wetlands and the diversion of their water for irrigation, turning desert plains into farmland, control of water levels in wetlands, feral cats and dogs, and the search for oil ^[4]. Former sites such as Puerto Viejo and Mollendo were lost to human disturbance ^[4].

At Paracas vehicle traffic through the colony is the greatest risk, because it can crush nests, eggs and chicks: 5 nests lay 30 m or less from a track, one of them at 1.5 m, and tracks multiplied after the Pisco earthquake of 15 August 2007 ^[6]. The 2025-2030 Master Plan of the Paracas National Reserve treats it as a priority species and lists as pressures vehicles driven in prohibited zones, small-scale fishing and the gathering of aquatic resources ^[2].

To reduce these conflicts it has been proposed to limit vehicles on beaches during the breeding season, mark trails, put up signs, run education in nearby towns and give legal protection to Pacasmayo, Tres Hermanas-Yanyarina and Paraíso ^[4]. At the Pampa El Palo colony the threats observed were human in origin: motor vehicle traffic, local fishers passing through and domestic dogs ^[8].

The Paracas Peninsula, in the Paracas National Reserve, holds the colonies of Pampa Lechuza and Pampa Atenas-Cequión, where in the 2006-2007 season more nests and birds were found than at other localities studied ^[6]. Its breeding area in the coastal desert is restricted: the Master Plan allows surveillance, control and biological monitoring by reserve staff there; research, photography and filming only exceptionally and with prior authorisation from the reserve headquarters; and motor vehicles only in exceptional cases ^[2].