Blue-gray Noddy Anous ceruleus Scientific name definitions

25–28 cm; 41–69 g (average 45·4 g, but non-breeders significantly lighter); wingspan 46–60 cm. Distinctive pale noddy  , with relatively short, slender black bill and short, slightly forked tail; all-grey head and body, with only slightly paler underparts  ; white partial spectacle behind eye  and small black spot in front; upperwing has slightly darker grey or brown-tinged coverts, and blackish primaries; below, shows little contrast between primaries and underwing-coverts; eye brownish black; bill and legs black. Smaller than A. albivitta, which is also paler grey above, and white below and on head. Races differ mainly in plumage tone, but some confusion exists; nominate ceruleus, at least in Marquesas, apparently darkest; teretirostris has paler head and underparts, but is significantly paler in Tuamotu Is than in Society Is.

Editor's Note: This article requires further editing work to merge existing content into the appropriate Subspecies sections. Please bear with us while this update takes place.

Genetic data suggest that both species formerly placed in Procelsterna should be included in genus Anous (1 Cibois, A., Thibault, J.-C., Rocamora, G. and Pasquet, E. (2016). Molecular phylogeny and systematics of Blue and Grey Noddies (Procelsterna). Ibis. 158(2): 433–438. Close ). Closely related to A. albivitta, with which often considered conspecific, but significant differences in size and coloration (see below); the two are sometimes incorrectly treated as pale and dark morphs of a single species; some authors have claimed that races skottsbergii and imitatrix of A. albivitta belong to present species, but specimen evidence refutes this. Internal taxonomy confused at present, with much overlap of forms, e.g. birds from Society Is significantly darker than those from Tuamotu Is and may not be referable to same race; validity of races and their distributions require careful systematic revision based on known breeding specimens, but these are lacking from various parts of the species’ range. Five subspecies currently recognized.

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 oceanic islands. Breeds on cliffs or rocky areas. Forages over lagoons and inshore waters.

Not known. Usually remains close to breeding colonies.

Has narrowest gape of any tern, and takes tiniest fish (average length 17 mm; mainly larval Synodontidae, Exocoetidae, Mullidae, Bothidae), squid, crustaceans, and pelagic sea striders (Halobates sericeus, H. micans); proportions vary seasonally and geographically. Fish present in 97% of samples, and squid in 50%. At Kiritimati over 50% of food items (75% of food volume) fish, with squid and crustaceans equally represented. At sea, species is the only primarily insectivorous pelagic tern. Usually feeds in small groups close inshore at breeding islands. Flies low over water with quick shallow wingbeats, dipping to surface to snatch tiny prey; often hovers low, foot-pattering on surface. Adults do not carry fish in bill.

In Hawaii reported to breed throughout year, with laying peak Feb–Mar, few nests in May, Aug and Nov, hence probably an asynchronous spring breeder, rather than truly aseasonal; Aug–Nov at Kiritimati, and Jun–Aug in Phoenix Is. On Hatutu, Marquesas Is, nests found in Jun, Aug, Sept and Nov (2 Thibault, J.-C., Cibois, A., Butaud, J.-F., Jacq, F.A., Poroi, E. and Meyer, J.-Y. (2013). Breeding birds of Hatuta’a, Marquesas Islands: species inventory and influence of drought on their abundance. Bull. Brit. Orn. Club 133(3):168–177. Close ). Loose colonies of up to 100 pairs on islets in lagoons. Nests on rocky substrate using crevice, ledge or concavity in cliffs or rock crops, or on gravel or coral rubble, usually on slopes; also under coral slabs or vegetation, seldom fully concealed; nest generally inaccessible to most predators. Usually no material, but may assemble a few shells, bones, feathers or stems around egg. Clutch single egg; incubation period not known; chick uniform whitish, with black bill and eye; hatching weight under 10 g; fed by regurgitation, and brooded continuously for 2–3 weeks. Productivity estimated at 0·5 young/pair on Nihoa (Hawaii); some eggs predated by Nihoa Finch (Telespyza ultima). Age of first breeding not reported, but some may breed at 1 year where nest-sites not limiting. Recorded longevity of 11 years.

Not globally threatened (Least Concern). Global population unknown but censuses over a small part of its range have recorded at least 30,000 pairs and the overall total may be closer to 100,000 pairs. The most numerous subspecies is probably nebouxi, which numbers well over 100,000 birds; race saxatilis is estimated at 10,000–25,000 birds and nominate at fewer than 10,000 birds (3 Wetlands International (2015). Waterbird Population Estimates. Wetlands International, Wageningen, The Netherlands. Close ). For NW Hawaii (saxatilis) there is an estimate of 4000 pairs plus 8000 non-breeders. Up to 10,000 pairs each in Line Is (nominate) and Phoenix Is (nebouxi); up to 1000 individuals in Gambier Is (murphyi) (4 Lacan, F. and Mougin, J.L. (1974). Les oiseaux des Îles Gambier et de quelques atolls orientaux de l'archipel des Tuamotu (Océan Pacifique). Oiseau et RFO. 44: 191-280. Close , 5 Waugh, S., Champeau, J., Cranwell, S. and Faulquier, L. (2013). Seabirds of the Gambier Archipelago, French Polynesia in 2010. Marine Ornithology 41(1):7–12. Close ), 2000 individuals on Kiritimati (nominate). Difficult to census as it uses inaccessible sea-cliff nesting sites, which protect it from egging and predators in most places. The availability of cliff nesting habitat is a limiting factor. The colony on Kaula I (Palmyra, Line Is) was eliminated when the island was used as a bombing range.