Lesser Frigatebird Fregata ariel Scientific name definitions

Restricted to Ilha da Trindade off the coast of Brazil (and rare even there), this relatively small frigatebird occurs elsewhere in the Western Hemisphere as an extremely rare vagrant. Primarily a bird of the southwest Pacific and Indian oceans, it has occurred just four times in North America, and is not known away from Trindade in South America. As with all frigatebirds, this species can wander, and observers should check all unusually plumaged or out-of-range frigatebirds with this species in mind.

66–81 cm (1 Howell, S. N. G., I. Lewington, and W. Russell (2014). Rare Birds of North America. Princeton University Press, Princeton, NJ, USA. Close ); male 625–875 g, female 760–955 g; wingspan 155–193 cm (1 Howell, S. N. G., I. Lewington, and W. Russell (2014). Rare Birds of North America. Princeton University Press, Princeton, NJ, USA. Close ). Much the smallest species. Smallest frigatebird. Breeding male is brownish black with blue, purple and greenish gloss on head  , neck, mantle and scapulars; upperwing lacks pale panel; has a diagnostic white crescent over central axillaries and anterior flanks; iris blackish brown; narrow bare eyering black or dark grey; bill mostly blackish grey to pale pinkish; gular pouch  bright red; legs pink or pink-red. Female is mostly blackish brown with little gloss, feathers of mantle browner with pale fringes; most of lesser upperwing secondary coverts similarly edged with pale brown to whitish, forming a noticeable diagonal wing panel; white variably tinged with buffy on chest down to central breast , foreflanks and axillaries, and linking to white collar on hindneck, but most of belly is dark; bare eyering pink or pink-red; bill pale bluish grey or light pink; legs pink. Juvenile  has apricot to tawny-brown head and neck down to central chest, variably mixed with whitish buff, separated from white belly, anterior flanks and proximal axillaries by broad blackish brown pectoral band; mantle and scapulars with pale brown or pale buff margins; upperwing has bold pale panel formed by broad sandy to whitish buff fringes to most of lesser and some median coverts; some contrast on underwing between forewing and browner more glowing remiges and underwing greater coverts; iris very dark; narrow bare eyering; bill and gular pouch pale blue-grey, more pale horn at tip; legs pale greyish or pale dull pinkish; later on, immature has less blackish on pectoral region, and gradually acquires adult plumage after several intermediate stages. Races based mainly on measurements, but far from being clear. Smallest frigatebird; adult male with diagnostic white crescents on sides of underparts, differs from <em>F. andrewsi</em> , the only other adult male frigatebird with white on underparts, by dark belly, smaller size and plainer dark upperwing, see text of Fregata minor for separation from some extreme males of that species; adult female has bold white collar conspicuous in lateral or dorsal view resembling larger F. andrewsi in this respect, differs from same plumage of all other congeners, especially from that of F. magnificens, in overall size, the abdominal white usually forming a triangular spur on axillaries springing from rear portion of white abdominal region (see F. andrewsi), in F. minor the white may reach to axillaries but in a broader and indistinct way and the hood in not complete and sharply contrasting with centre of breast, from F. magnificens also by eyering colour. Juvenile differs from others by size and by relatively narrow triangular white ventral patch, from that of F. minor by much more dark brown across pectoral area, and from F. magnificens also by having solid white spur on axillaries.

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Editor's Note: Additional distribution information for this taxon can be found in the 'Subspecies' article above. In the future we will develop a range-wide distribution article.

Tropical and subtropical seas, breeding on small, remote islands , in mangroves or bushes/scrub (Pemphis, Lepturus, Tournefortia); more prepared to use lower vegetation than F. minor on Aldabra, and can even nest on ground, e.g. in Phoenix and Line Is (SC Pacific), Raine I (NE Australia). Feeds in adjoining ocean, usually in waters over 22°C in pelagic zone.

Sedentary, with dispersal of immatures and non-breeders throughout tropical seas, especially across Indian and Pacific Oceans. Results from ringing of some 13,000 juveniles in SC Pacific indicate that they follow prevailing winds W to Coral Sea, NE of Australia, before heading N via New Guinea towards Philippines, with some reaching Japan and NE Russia (up to 10,000 km from their breeding sites) (1 Howell, S. N. G., I. Lewington, and W. Russell (2014). Rare Birds of North America. Princeton University Press, Princeton, NJ, USA. Close ); recent evidence suggests possible mixing with Australian birds, with some heading further W, e.g. to Cocos (Keeling) Is; may be attempting to colonize Christmas I, Indian Ocean. As many as 5000 individuals have been recorded at mixed Fregata roost on Mantanani Is (Sabah) (3 Robson, C. (2014). From the field. BirdingASIA. 21:121–127. Close ) and up to 1000 per day passed Buru in Oct 1995 (4 Reeve, A. H., T. Haryoko, M. K. Poulsen, P.-H. Fabre, and K. A. Jønsson (2014). New ornithological records from Buru and Seram, south Maluku, Indonesia, 1995–2012. Forktail 30:10–22. Close ). Four records from North America, all in late summer and autumn (Jul to mid Sept), from Maine (Jul 1960), Wyoming (Jul 2003), Michigan (Sept 2005) and California (Jul 2007) (1 Howell, S. N. G., I. Lewington, and W. Russell (2014). Rare Birds of North America. Princeton University Press, Princeton, NJ, USA. Close ). Several records from India, one of them 175 km inland (5 Huilgol, A. K. (2007). Sighting of the Lesser Frigate Bird Fregata ariel at Ranganathittu Bird Sanctuary, Karnataka. Indian Birds. 3(3): 103–104. Close ), with additional observations from Andaman and Nicobar Is, including a flock of 28 in Jun 1997 (6 Sivakumar, K. and Sankaran, R. (2002). New records of birds from the Andaman and Nicobar Islands. Forktail. 18: 149–150. Close ), and a recent record (Dec 2013) from Mekong R, on Thai/Lao border, at least 300 km inland (7 Limparungpatthanakij, W. (2014). A Lesser Frigatebird Fregata ariel seen over the Mekong River on the Thai-Lao border. BirdingASIA. 21: 113–114. Close ), while in New Guinea species has not only been observed well inland but also at highland localities up to 2750 m above sea-level (8 Beehler, B. M., and T. K. Pratt (2016) Birds of New Guinea: distribution, taxonomy, and systematics. Princeton University Press, Princeton, New Jersey. Close ). Vagrant to China, Japan, Siberia, NE USA and New Zealand  . Has also wandered to Oman (five records, Jul–Oct), Kuwait, Yemen and S Israel (two records) (9 Aspinall, S. and Stanton, D. (2010). Lesser Frigatebird Fregata ariel new to Yemen. Sandgrouse. 32(1): 41–42. Close , 10 Van Welie, L. (2000). Lesser Frigatebird at Eilat, Israel, in May 1999. Dutch Birding. 11: 16–17. Close ).

Mostly fish, especially flying fish (Cypselurus, Exocoetus, Evolantia) of 10–20 cm, and squid (Ommastrephidae) of 4–12 cm; also seabird eggs and chicks, carrion and fish scraps. Surface-dipping main method for obtaining food. Kleptoparasitism , of such species as Masked Booby (Sula dactylatra) and noddies (Anous), occurs but available evidence suggests that it accounts for relatively minor proportion of diet. One study found no sex-specific differences in kleptoparasitic behaviour, unlike that reported for F. minor (11 Congdon, B. C. and Preker, M. (2004). Sex-specific chick provisioning and kleptoparasitism in the Least Frigatebird, Fregata ariel. Emu. 104: 347–351. Close ).

Usually silent away from colonies. Calls at nest include several rather gull-like grating and squealing calls, plus hissing; lacks warble during display of F. andrewsi and F. minor. Arrival call of male a series of short whistles, “weese-weese-weese”, while female emits a chicken-like “kaaaa-chuk-chuk-chuk-chuk-chuk”. Also mechanical bill-clapping by both sexes.

Throughout much of year at different localities; some preference for egg-laying in dry season. Probably biennial, when successful. Colonial , with sub-groups of up to 100 nests; often in mixed colonies alongside other species of Pelecaniformes, sometimes with F. minor. Nest is stick platform, usually up to 15 m up tree. Single egg  ; incubation c. 45 days; chicks naked, grow white down ; fledging 20–24 weeks; post fledging care 4–6+ months. Age of sexual maturity unknown. Success (eggs to fledging) 12% Aldabra. Association of unpaired males in communal display groups and clustering of nests around these display sites, as generally described for frigatebird species, may not occur in present species: study on Aldabra found that unpaired males did not form stable display clusters, aggregating only at sites of female interest, remained for short periods and did not fight for display sites. Unlike female F. minor, females of present species perform ritualized aerial display before landing beside an advertising male, begin settlement soon after first male display, and show no preference for colonies of different size (12 Reville, B. J. (1991). Nest spacing and breeding success in the Lesser Frigatebird (Fregata ariel). Condor. 93: 555–562. Close ).

Not globally threatened (Least Concern). World population probably several hundred thousand birds; main threats are probably habitat destruction, disturbance and direct persecution by humans for food. Several thousand pairs in Indian Ocean, including 6000+ at Aldabra; minimum c. 15,000 pairs on islands off N & E Australia (13 Walker, T. A. (1992). A record Crested Tern Sterna bergii colony and concentrated breeding by seabirds in the Gulf of Carpentaria. Emu. 92: 152–156. Close ); most spectacular numbers in SC Pacific, where both Phoenix and Line Is may hold tens of thousands of pairs, with possible breeding in another ten island groups; El Niño Southern Oscillation events can cause partial or total breeding failure in C Pacific. Atlantic race trinitatis may deserve species status (14 Olson, S. L. (2017). Species rank for the Critically Endangered Atlantic Lesser Frigatebird (Fregata trinitatis). Wilson Journal of Ornithology 129(4):661–675. Close ). It formerly bred on St Helena and possibly also Martin Vaz Is, but is now restricted to Trindade, off E Brazil, where fewer than 20 pairs were found breeding on a small islet in 1975/76 (estimated maximum population of 50 birds) (15 Olson, S.L. (1981). Natural history of vertebrates on the Brazilian islands of the Mid South Atlantic. Natl. Geog. Soc. Res. Reports 13: 481-492. Close , 14 Olson, S. L. (2017). Species rank for the Critically Endangered Atlantic Lesser Frigatebird (Fregata trinitatis). Wilson Journal of Ornithology 129(4):661–675. Close ). During 60 days of surveys in 2013, only six birds (two adult males, two adult females and two juveniles) were recorded, and no nesting observed (16 Port, D., Branco, J.O., Alvarez, C.E. and Fisch, F. (2016). Observations on endangered frigatebirds (Fregata ariel trinitatis and F. minor nicolli, Suliformes: Fregatidae) at Trindade Island, Brazil. Pan-American Journal of Aquatic Sciences. 11(1): 87–92. Close ). Decline of trinitatis may have been caused by a combination of factors, including suppression of the regeneration of nesting trees by pigs (Sus scrofa) and goats (Capra aegagrus hircus), introduced as early as 1700 but extirpated in 1965 and 2005 respectively; tree cover began to disappear by the 19th century (14 Olson, S. L. (2017). Species rank for the Critically Endangered Atlantic Lesser Frigatebird (Fregata trinitatis). Wilson Journal of Ornithology 129(4):661–675. Close ). Over-fishing of the waters around the islands and direct consumption of eggs have also been postulated as contributors to the decline (16 Port, D., Branco, J.O., Alvarez, C.E. and Fisch, F. (2016). Observations on endangered frigatebirds (Fregata ariel trinitatis and F. minor nicolli, Suliformes: Fregatidae) at Trindade Island, Brazil. Pan-American Journal of Aquatic Sciences. 11(1): 87–92. Close ). Feral cats (Felis catus) were present 'in substantial numbers' on Trindade and are likely to have predated birds; they were eliminated by 1994. House mice (Mus musculus) remain abundant and are likely to prevent recolonisation of the main island (14 Olson, S. L. (2017). Species rank for the Critically Endangered Atlantic Lesser Frigatebird (Fregata trinitatis). Wilson Journal of Ornithology 129(4):661–675. Close ). Taxon trinitatis is considered Critically Endangered at the national level in Brazil (17 Silveira, L. F., and F. C. Straube (2008). Aves. Pp. 378–679 in:. Close , 18 MMA (2014). Lista Nacional Oficial de Espécies da Fauna Ameaçadas de Extinção. Portaria No 444, de 17 de dezembro de 2014. Diário Oficial da União - Seção 1. Nº 245, quinta-feira, 18 de dezembro de 2014. Close ).