Description

It is the only booby regularly encountered on Diego Garcia and hundreds can be observed in the early evening passing the Downtown area, returning to the islets in the mouth of the lagoon to roost. Over 99.9% of the birds occurring in BIOT are of the wholly white morph; though there are two records of two white-tailed brown morph birds on Diego Garcia in 1995 and in November 2008 and again in November 2009, in the same nest, a brown morph adult was found incubating on Petite Coquillage, Peros Banhos.

Identification Guide: A beautiful bird in breeding plumage, the intensity of the colours of the feet and bill increase as peak breeding condition is reached. Adults are readily distinguishable by their black and white wings with a distinctive black patch at the bend of the wing on the underside and the diagnostic yellow on the head. Juveniles require more care in identifying them from the other two booby species: the all-brown body of juveniles of this species is diagnostic.

Status and Distribution: Common breeding resident. This is the commonest Sulidae occurring in BIOT, found throughout the entire Territory. It appears to be expanding its range into areas that it most likely formerly bred in and has seemingly increased in numbers since at least 1970. It has (re)colonised the now uninhabited Salomon Islands since at least 1996, when this atoll was surveyed and no birds were found breeding; in November 2008, there were over 100 pairs breeding on Mapou and smaller numbers on Ile du Passe and Takamaka. It has also (re)colonised the Egmont Islands with at least 30 pairs breeding on Ile Carre Pate in February 2010. On Diego Garcia in 1971, it was only ever recorded on the lagoon islets; by 2010, there were an estimated 5,325 breeding pairs, nesting from Cust Point ocean-side to Shark's Cove lagoon-side. It has a very complicated breeding phenology, with differing breeding periods in the same colony as well as between islands and atolls. The peak breeding period appears to be between December and April, though breeding birds can be found on all atolls throughout the year.