Blue-footed booby

Sula nebouxii is a seabird of the family Sulidae described by Milne-Edwards in 1882 ^[1]. In Peru it is called «camanay» ^[2] and also «piquero patas azules» ^[3]. It breeds in the Gulf of California, the Gulf of Panama, Galápagos and on Lobos de Tierra and Lobos de Afuera islands in northern Peru ^[4]. On Lobos de Tierra Island it feeds mainly on anchoveta, which it catches by plunging into the water from the air ^[5]. The IUCN Red List classifies it as Least Concern ^[6].

Females are clearly bigger than males. On Lobos de Tierra Island, 169 females averaged 1723 g (between 1350 and 2000 g) and 139 males 1319 g (between 1125 and 1500 g); females turned out 31 % heavier and between 6 and 9 % larger in body measurements, and their wing chord averaged 43.27 cm against 40.92 cm in males ^[5].

Eye and voice also tell the sexes apart: the dark patch in the centre of the iris is larger and more irregular in the female, and the male gives whistles while the female grunts ^[5]. The iris is yellow, and in the male the pupil looks small ^[7].

In males, the blue of the feet combines a structural component, made of ordered collagen fibres, with pigments; in an experiment, their feet grew duller within 48 hours when food was withheld and brightened again once they were given fresh fish, and changes in dietary carotenoids shifted both colour and immune response together ^[8].

Similar species

• Sula variegata: The Peruvian booby has red eyes and grey legs, whereas Sula nebouxii has yellow eyes ^[7]. The secondary wing feathers of the Peruvian booby carry a variegated pattern that the brown secondaries of Sula nebouxii lack; on Lobos de Tierra and Lobos de Afuera intermediate birds have been seen, with a light brown head, orange eyes and grey legs ^[4].

It breeds in the Gulf of California, the Gulf of Panama, Galápagos and, in Peru, on Lobos de Tierra and Lobos de Afuera islands, where it lives alongside the Peruvian booby but far outnumbers it ^[4]. A genetic study sampling 173 juveniles at 9 colonies between Mexico and northern Peru found weaker differentiation between colonies than in any other tropical booby studied, with much gene flow within Mexico and within the southern part of the range but less between the two regions; the authors put that weak differentiation down to greater dispersal, which they link to its specialisation in cold upwelling waters ^[9].

In Peru its breeding islands lie where the cold Peruvian Current meets warm, nutrient-poor water from the equatorial Pacific, and there it nests on flat ground and on slopes ^[7]. Lobos de Tierra is an arid island of about 1426 ha, 12 km from the mainland; in 2002 and 2003 the colonies covered almost two-thirds of its surface, with nests spread evenly in subcolonies of up to 10000 pairs, separated by rocky hills ^[5].

In the 2014 monthly counts on the islands and headlands of the Reserva Nacional Sistema de Islas, Islotes y Puntas Guaneras it turned up almost only on those two islands; farther south numbers were much lower and did not recur every month, peaking at 960 birds on Isla Chao in June, and it reached as far as Punta San Juan, where 8 birds were counted in June ^[2].

On Lobos de Tierra it breeds all year round, although hatching peaks at the end of December ^[5]. Raising a chick takes it 5 to 6 months: some 42 days of incubation, about 100 days of rearing in the nest and at least 28 more days in which the parents keep feeding the fledged young at the colony ^[10]. In the 2003 season, 88 % of the adults measured on Lobos de Tierra were moulting tail feathers while tending their chicks ^[5].

The colour of the male's feet tells the female about his condition: when, the day after the first egg was laid, the feet of some males were painted a duller blue, their mates laid a smaller second egg than control females did, which makes it easier for the brood to be reduced ^[8]. With age and accumulated breeding seasons the colour of the male's feet deteriorates, but males that skip a year of breeding show showier feet than those that bred the year before ^[11].

Genetic analysis of 5 intermediate-looking birds caught on Lobos de Tierra and Lobos de Afuera confirmed that they were hybrids with the Peruvian booby: 4 were males and 1 a female, and all carried Peruvian booby mitochondrial DNA; according to the authors, such crosses seem rare and confined to the islands where both species breed ^[12].

On Lobos de Tierra, between 2002 and 2003, regurgitations held 16 species of fish and 1 of squid, but anchoveta (Engraulis ringens) dominated with 79 to 97 % of the mass; 80 % of the anchoveta were adults of 11 cm or more, and females ate somewhat larger prey than males ^[5].

It fishes by day, with plunge dives. Depending on sex and year, the mean depth of dives was 3.3 to 5.1 m; females went deeper and stayed down longer than males, the deepest dive reached 22 m and the deepest ones clustered between 10:00 and 14:00 ^[5]. Each fishing trip lasted about 3 hours on average, and 86 % of that time was spent flying ^[5].

Using direction recorders, 26 birds from Lobos de Tierra were followed over 59 trips: they mostly headed east of the island, over the continental shelf and its cold waters, where anchoveta is usually more plentiful; the farthest point from the colony lay at a median of 39 km (between 3 and 109 km) and 90 % of trips stayed less than 30 km from the coast ^[13]. In the winter of 2002 they went farther and into more oceanic waters than in the summer of 2003, in step with the seasonal shifts of anchoveta ^[13].

Its global category is Least Concern ^[6]. In the direct-use zone of Lobos de Tierra Island, the 2026-2031 master plan of the Reserva Nacional Sistema de Islas, Islotes y Puntas Guaneras requires its resting and breeding areas, like those of other guano birds, to be kept undisturbed, and guano to be harvested only when guano birds are not courting, nesting or rearing chicks ^[14].

In the Reserva Nacional Mar Tropical de Grau, informal tourism that lands on Isla Foca or sails close inshore disturbs the nesting and resting areas of guano birds, this species among them, and causes nest desertion; at Punta Veleros, urban growth threatens a refuge for boobies ^[3].

H5N1 avian influenza also struck it: by 29 November 2022, SERFOR had counted 614 dead camanay among more than 13869 seabirds killed by the virus along the Peruvian coast ^[15].

In Galápagos, the archipelago's own population has bred poorly since 1998 and, in a 2012 census, numbered about 6400 adults, against a rough estimate of 20000 in the 1960s; the authors link the problem to sardines all but vanishing from its diet ^[10].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

During the 2022 H5N1 avian influenza epizootic, SERFOR advised people not to approach seabirds or take them home, so as not to spread the virus or infect poultry, and asked for every case to be reported to the authorities ^[15].

On Lobos de Tierra, the area where it rests and breeds is the same one where AGRO RURAL harvests island guano, an activity carried out there historically ^[14].

In Galápagos the authors of one study call it an icon of biodiversity and of ecotourism, and warn that its decline in the archipelago has important implications for both ^[10].

Its large Peruvian colonies are on Lobos de Tierra and Lobos de Afuera islands. In the 2014 monthly counts up to 239980 birds were estimated on Lobos de Tierra, in January, and up to 60000 on Lobos de Afuera, in March and April ^[2]. On Lobos de Tierra a breeding population of 75000 to 100000 pairs was estimated in 2002 and 2003 ^[5].

Both islands belong to the Reserva Nacional Sistema de Islas, Islotes y Puntas Guaneras, and in the wild zones of Lobos de Afuera where it rests and breeds even research and photography need prior assessment and authorisation from the reserve's headquarters ^[14]. Lobos de Afuera lies 93 km west of Lambayeque, and in 2004 and 2005 the researchers who visited it held an entry permit from Proabonos, the guano extraction company ^[4].

According to the 2026 master plan of the Reserva Nacional Mar Tropical de Grau, it also nests on Isla Foca, mainly on the cliffs ^[3], and keeps permanent populations on cliffs in the reserve ^[3]. The upper part of Isla Foca, where it nests with the Peruvian pelican and the guanay cormorant, is a strict protection zone: people may not enter it, nor sail, swim or dive there ^[3].

It also appears, as «piquero de pata azul», in the 2023 bird list of the Santuario Nacional Los Manglares de Tumbes ^[16].