Magnificent frigatebird

Fregata magnificens is a seabird of the family Fregatidae, described by Mathews in 1914 ^[1]. In Peru, the master plan of the Los Manglares de Tumbes National Sanctuary lists it as «avefragata magnífica» ^[2]. The authors of the IMARPE study describe it as the largest and most coastal, and in Peru its only known breeding colony is on Los Pájaros Island, in Tumbes ^[3]. When the sea warms abnormally, as in El Niño episodes, it was recorded farther south than usual ^[3].

It lives mostly in tropical seas: in the Pacific from California to Ecuador, the Galápagos Islands included, and in the Atlantic from Florida to southern Brazil, taking in the whole Caribbean Sea ^[3]. The total nesting population is estimated at 59000 to 71000 pairs, and the largest colonies are in Baja California and the eastern Pacific, with 48000 to 58000 pairs ^[3].

Along the Peruvian coast, IMARPE monitoring and cruises between October 2015 and December 2019 added up to 73 sightings and 646 birds between 4° S and 7° S; 622 of those birds were counted at 4° S and 5° S, and the largest number, 383, at 5° S, off Paita ^[3]. At 4° S, 5° S and 7° S most of the birds were within 10 miles of the coast, whereas at 6° S they were seen beyond 20 miles ^[3].

Its usual southern limit moves with the warmth of the sea. In El Niño 2015-2016 and El Niño Costero 2017 it reached 8° S, off Chicama, whereas from May 2017 to December 2019 it was recorded only as far as 5° S, in waters of about 19 to 20 °C ^[3]. The authors also cite a study that recorded birds during El Niño periods even at Pantanos de Villa, in Lima, at 12° S, an area outside its normal range ^[3].

It builds stick nests in trees or shrubs: the male supplies the material and the female assembles the nest ^[3]. In Peru it nests at a single known place, Los Pájaros Island, within the Los Manglares de Tumbes National Sanctuary, where 1643 active nests were counted ^[3].

Among all the birds of the world, frigatebirds have the lowest ratio of body weight to wing area, which lets them take off easily and glide for hours on high thermals ^[3]. With short legs, very large wings and a small uropygial gland, which oils the plumage, they are never seen resting on the water and take their food from the surface ^[3]. In Peru, sightings of flying birds were concentrated between 06:00 and 18:00 hours, with 179 individuals at 06:00 and 171 at 10:00 ^[3].

In the Caribbean, on the Cayman Islands, birds rearing chicks were followed with GPS loggers and cameras: some trips were coastal, over the continental shelf, and others went out to sea; males ranged farther from the nest and went out to open sea more often than females ^[4].

It is also known as the pirate of the seas because it chases other seabirds in flight, mainly boobies, until they regurgitate, and takes their food; it also makes use of fishing waste ^[3]. Reported prey include flying fish, squid, jellyfish, turtle hatchlings, eggs and chicks of seabirds, and fish remains ^[3].

At the Dry Tortugas, off the Florida Keys, researchers compared how adult and subadult birds go about stealing food ^[5]. Adult females approached other birds mostly in the air (92% of encounters), whereas subadults did so more with birds on the ground (61%); approaches from the water were rare in subadults and made by no adult ^[5]. Adult females spent more time on each chase and sought out solitary birds (69%), whereas subadults seemed to prefer groups (78%) ^[5].

On the northern coast of Peru, the authors of the IMARPE study suggest that the greater concentration between 4° S and 5° S could be due to the distance between colonies and to the birds travelling near the coast because of the food available by fishing ports, and that their southward movements in warm years could use rising warm air to spend little energy ^[3].

The bird list in the master plan of the Los Manglares de Tumbes National Sanctuary assigns it no threat category under Supreme Decree 004-2014-MINAGRI; it is among the 158 bird species recorded in the sanctuary between 2015 and 2020 ^[2].

Even so, the species depends on few places: in Peru only one breeding colony is known ^[3]. Human disturbance and introduced predators have eliminated many historical colonies of the species, and this is likely to continue as more coastal areas are developed ^[3].

The IMARPE authors argue that the appearance of this bird farther south than usual coincides with warm events, so it could serve as a biological indicator of the warming of surface waters during anomalous episodes such as El Niño ^[3].

It also feeds on fishing waste, so it cleans coves and fishing ports along the coast, and its droppings fertilise the waters of the mangroves with nutrients used by the vegetation ^[3].

In the IMARPE monitoring and cruises of 2015 to 2019, the largest number of birds was counted at 5° S, off Paita, and at 4° S, and at 4°, 5° and 7° S most were within 10 miles of the coast ^[3].

Its only known breeding site in Peru is Los Pájaros Island, in the Los Manglares de Tumbes National Sanctuary ^[3], an area where it is included among the birds recorded from 2015 to 2020 ^[2].