Gull-billed tern

    Sterna nilotica

Castilian: Pagaza piconegra

Catalan: Curroc

Gallego: Carrán de bico curto

Euskera: Txenada mokobeltza

CLASIFICACIÓN:

Orden: Charadriiformes

Family: Sternidae

Migratory status: Summer resident

CONSERVATION STATUS:

On the National List of Threatened Species, it appears in the “Of Special Interest” category. In the 2004 edition of the Red Book of Spanish Birds (Libro Rojo de las Aves de España) it is listed as “Vulnerable”.

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THREATS

Its own reproductive behaviour represents a problem given that the reproductive population is concentrated in very few areas and because it breeds in islets, which can cause the nests to be swept away by flood waters or, if they dry up, can leave the nests vulverable to predators (foxes, rats, and other mammals). The presence of aerial predators, such as falcons and gulls, is important, as is the drying up of wetlands. Another problem is the disappearance of the food supply that the species used to obtain due to agricultural intensification, the abuse of pesticides, and the elimination of unfarmed land and wastelands.

Length / size: 33-43 cm / 85-103 cm

Identification: Medium- to large-sized tern with a short, thick, black bill, long and slightly angled wings, and a forked tail. Its plumage on its back is light grey, its underparts are white, and it has a dark spot behind the eye that turns into a pointed hood during mating season, extending across the nape and reaching the back.

Song: Very noisy in colonies. It makes a fast "gweek gweek gweek" when alarmed, while in flight its normal call is a nasal and deep "gareek".

Diet: It feeds on insects, specifically ortopterans (grasshoppers) and beetles, although its diet also includes other types of invertebrates.

Reproduction: It breeds in colonies, whether they are monospecific or mixed (with other gulls or waders), and breeding begins in late April. It nests in islets with certain amounts of plant cover. Both adults incubate the eggs and feed the chicks. Within a few days of birth, the chicks leave the nest to take refuge in the vegetation.

HABITAT

It occupies vast wet areas, near water, with subaquatic vegetation and with islets with little vegetation where it installs its nests; these can be lagoons, river deltas, marshes, steppe lakes, etc.

DISTRIBUTION

In Spain: It is distributed throughout the southern half and certain areas of the Mediterranean basin. During breeding season, it is concentrated in the Guadiana basin and the Guadalquivir marshes, and to a lesser extent in the Tajo basin and the Ebro Delta.

In Castile and León: Routine presence in Villafáfila (Zamora), its only breeding place.

Movements and migrations: Migratory species that reaches our latitudes in April and leaves in August. Northern European populations migrate to their wintering areas in the western coasts of Africa and in the region of the River Niger by crossing the Iberian Peninsula, generally by going through inland areas. Because of this, it can be observed in prenuptial passage in March and postnuptial passage in until September.

POPULATION

In Spain: There is an estimated population of 3000-3500 breeding pairs.

In Castile and León: