The blue-footed bird that fascinated Darwin

Blue-footed booby (Sula nebouxii) was studied by Charles Darwin during his trip to the Galapagos Islands. Definitely, this bird is a wonder of the evolution of the species. We will know more about this amazing bird that is increasingly threatened.

1. WHERE TO FIND IT AND HOW TO RECOGNIZE IT

The Blue-footed booby (Sula nebouxii) is a species of bird of the order Suliformes (gannets and other related birds), family Sulidae (gannets or piqueros), from the American Pacific. They are medium-large-sized coastal birds that feed on catching fish diving on the water. It is distributed along the coasts between Peru and the Gulf of California, and the Galapagos Islands.

map-blue-footed-booby-160-2999-cb1447107513_national geographic
Picture 1: Blue-footed booby distribution map. Source: http://www.nationalgeographic.com

Blue-footed booby is unmistakable for its curious and striking bright blue paws, as its name suggests. However, this characteristic is only present by adult birds, since when they have not yet completed their development the chickens have pale legs as part of their survival strategy to avoid drawing attention to possible predators. To differentiate between adult males and females, we must look at two characters: size, males are smaller than females; and the unmistakable difference in their pupils, larger in females.

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Picture 2: Blue-footed booby male (on the left) and female (on the right), can be observed the difference in the size of their pupils. Source: www.stillnotgrowup.com

They feed mainly on pelagic fish such as pilchards (Sardinops caeruleus), chub mackerel (Scomber japonicus) and flying fishes (Exocoetus sp.). It is fascinating to watch the activity of these birds while they feed: they fly over the sea and dive from the air after their prey, entering the water at high speed, reaching speeds of up to 96 km / hour. This same technique to obtain food is carried out by all the pikemen and gannets. It is a gregarious species both for breeding and feeding, so it is common to see groups of birds hunting in the sea.

pesca_Tui De Roy_Miden Pictures
Picture 3: Group of blue-footed booby feeding on the sea by the diving technique. Source: Roy Tui via Miden Picture.

2. WHY GANNETS AND OTHER CURIOSITIES

Blue-footed booby is a bioindicator species, reflecting both oceanic conditions and marine productivity. They change their diet and growth rate of the chicks according to the available food (Maccall,1982; Ricklefs et al., 1984; and Jahncke and Goya, 2000), as well as their distribution pattern in the marine region during the breeding season (Valle Castillo, 1984; Hayes and Baker, 1989; Tershy et al., 1991).

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Picture 4: Bird resting on rocks in Puerto Ayora, Ecuador. Source: Emilio, Erasmus Photo Puerto Ayora

Courting behavior is very complex (Parkin et al., 1970, Nelson, 1978, Rice, 1984), and its striking blue paws play a very important role. The male shows his legs to the female during the ritual, as it is one of the characters that the female takes into account in the choice of her partner. The color of the legs is due to the accumulation of carotenoids obtained from their diet, which is used as a breeding strategy: it reflects the health status of the individual and increases the chances of success. However, it has been shown that this strategy is not limited to a preference of the females for males with brighter blue paws, but also males show preference for females with brighter colored legs and thus, they may have a higher probability of interactions with other males other than his partner (Torres and Velando, 2003), despite being a monogamous species.

3. THE BLUE-FOOTED BOOBY IN YEARS OF CHANGES

‘El Niño’ is a cyclical climatic phenomenon (every 2-7 years) that wreaks problems worldwide, with the most affected areas being South America and the areas between Indonesia and Australia, causing water warming and huge changes in climate, as it causes severe droughts and floods. Its origin is related to the level of the oceanic surface and its thermal anomalies. The ‘El Niño’ phenomenon reverses the Humboldt current, which brings cold, nutrient-rich water from Antarctica, and warm equatorial water arrives instead, decreasing the number of birds that may depend on marine life.

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Picture 5: ‘El Niño’ phenomenon process. Source: http://www.ecuadordelsur.blogspot.com.es

In years of the ‘El Niño’ phenomenon, the blue-footed booby modifies its habits feeding on coastal fish almost exclusively (Carboneras 1992, Jancke and Goya 2000). In addition, it has been observed that this phenomenon influences its reproduction being negatively affected parameters such as laying size, hatching, success in flying chicks, … related to the low ocean productivity that causes this phenomenon (Wingfield, 1999).

Blue-footed Booby
Picture 6: Laying and hatching of eggs. Source: http://www.darwinfoundation.org

Currently, scientists have shown that due to global warming the frequency of El Niño has increased, and this seriously threatens the survival of the species in Galapagos since it may assume that there is not enough time for the species to recover, leading to their populations to very low populations and even to extinction.

4. A HARD START FOR CHICKS

The blue-footed booby lays 1-3 eggs incubated for 41 days. Chicks fly about 102 days and parents continue to feed them until their full independence.

pollosyprogenitor_Tui de Roy_Miden Pictures
Picture 7: Father and chicks. Source: Tui de Roy, Miden pictures

In clutches, usually two chickens, a hierarchy is usually established in which the first-born chicken is dominant in front of its smaller brother and receives more food from the parents. It is a species that can present or not the phenomenon of reduction of the clutch by means of the fraticide (Anderson, 1989, Anderson and Ricklefs, 1992), causing the older brother the death of the smaller one. In one way or another, the brother born last will have a difficult beginning because he will have to compete with his older brother for food in a continuous struggle for survival.

Blue-footed Booby
Picture 8: Clutches are usually of two chickens and the older brother shows dominance over the small. Source: http://www.darwinfoundation.org

5. REFERENCES

  • CONABIO – www.biodiversidad.gob.mx
  • Effect of food deprivation on dominance status in blue-footed booby (Sula nebouxii) broods – Miguel A. Rodriguez-Girones,” Hugh Drummond,b and Alex Kacelnik’ – Behavioural Ecology, 1996
  • Male preference for female foot colour in the socially monogamous blue-footed booby, Sula nebouxii – Animal Behaviour, 2005 – Roxana Torres, Alberto Velando.
  • Maternal investment in eggs is affected by male feet colour and breeding conditions in the blue-footed booby, Sula nebouxxi – Behavioral Ecology and Sociobiology, 2008 – Fabrice Dentressangle, Lourdes Boeck and Roxana Torres
  • The Effects of an “El Niño” Southern Oscillation Event on Reproduction in Male and Female Blue-Footed Boobies,Sula nebouxii – John C. Wingfield, Gabriel Ramos-Fernandez, Alejandra Núñez-de la Mora, Hugh Drummond – General and Comparative Endocrinology, 1999
  • http://www.lareserva.com/home/Alcatraz_patas_azules
  • http://www.iucnredlist.org/
  • Cover photo: Credit Asahi Shimbum vía Getty Images

Sara de la Rosa Ruiz

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