Sulidae – Gannets & Boobies

Red-footed Booby Sula sula ©Gregg Yan (Creative Commons) Website

The bird family Sulidae comprises the gannets and boobies. Collectively called sulids, they are medium-large coastal seabirds that plunge-dive for fish and similar prey. The ten species in this family are often considered congeneric in older sources, placing all in the genus Sula. However, Sula (true boobies) and Morus (gannets) can be readily distinguished by morphological, behavioural and DNA sequence characters. Abbott’s booby (Papasula) is given its own genus as it stands apart from both in these respects. It appears to be a distinct and ancient lineage, maybe closer to the gannets than to the true boobies

Sulids measure about 60 to 85 cm in length and have a wingspan of about 140 to 175 cm. They have long, narrow and pointed wings, and a quite long, graduated and rather lozenge-shaped tail whose outer feathers are shorter than the central ones. Their flight muscles are rather small to allow for the small cross section required for plunge-diving, and thus their wing loading is high. Consequently, they are very streamlined, reducing drag, so their bodies are “torpedo-shaped” as well as somewhat flat.

They have stout legs and webbed feet, with the web connecting all four toes. In some species the webs are brightly coloured and used in courtship displays. The bill is usually conspicuously coloured, long, deep at the base, and pointed, with saw-like edges. The upper mandible curves down slightly at the tip and can be moved upward to accept large prey. To keep water out during plunges, the nostrils enter into the bill rather than opening to the outside directly. The eyes are angled forward, and provide a wider field of binocular vision than in most other birds.

The plumage is either all-white (or light brownish or greyish) with dark wingtips and (usually) tail, or at least some dark brown or black above with white underparts; gannets have a yellowish hue to the head. The face usually has some sort of black markings, typically on the lores. Unlike their relatives (the darters and cormorants), sulids have a well-developed preen gland whose waxy secretions they spread on their feathers for waterproofing and pest control. They moult their tail feathers irregularly and the flight feathers of their wings in stages, so that starting at the first moult, they always have some old feathers, some new ones, and some partly grown ones. Moult as a response to periods of stress has been recorded

The sulids are distributed mainly in tropical and subtropical waters. Particularly gannets, however, are found in temperate regions too. These birds are not truly pelagic seabirds like the related Procellariiformes, and usually stay rather close to the coasts. But the abundant colonies of sulids that exist on many Pacific islands suggest that they are not infrequently blown away from their home range by storms, and can wander for long distances in search of a safe place to land if need be.

All species feed entirely at sea, mostly on mid-sized fish and similarly-sized marine invertebrates such as cephalopods. Many species feed communally, and some species follow fishing boats to scavenge discarded by-catch and chum. The typical hunting behaviour is to dive from mid-air, which takes the bird a meter or two under water. If their prey manages to escape the diving birds at first, they may give chase using their legs and wings for underwater swimming.

There are just 10 species in the Sulidae familly; they are:

Northern Gannet Morus bassanus Linnaeus, 1758

Cape Gannet Morus capensis Lichtenstein, MHK, 1823

Australasian Gannet Morus serrator Gray, GR, 1843

Abbott’s Booby Papasula abbotti Ridgway, 1893

Blue-footed Booby Sula nebouxii Milne-Edwards, 1882
S. n. nebouxii Milne-Edwards, 1882
S. n. excisa Todd, 1948

Peruvian Booby Sula variegata Tschudi, 1843

Masked Booby Sula dactylatra Lesson, R, 1831
S. d. dactylatra Lesson, R, 1831
S. d. melanops Hartlaub, 1859
S. d. tasmani van Tets, Meredith, Fullagar & Davidson, P, 1988
S. d. personata Gould, 1846

Nazca Booby Sula granti Rothschild, 1902

Red-footed Booby Sula sula Linnaeus, 1766
S. s. sula Linnaeus, 1766
S. s. rubripes Gould, 1838
S. s. websteri Rothschild, 1898

Brown Booby Sula leucogaster Boddaert, 1783
S. l. leucogaster Boddaert, 1783
S. l. brewsteri Goss, 1888
S. l. etesiaca Thayer & Bangs, 1905
S. l. plotus Forster, JR, 1844

Number of Species
  • Number of bird species: 10

Useful Reading
  • Pelicans, Cormorants and their Relatives - The Pelicaniformes

    by J Bryan Nelson, illustrated by John Busby, Andrew Mackay and Bas Teunis OUP 2005
    See Fatbirder Review ISBN: 0198577273 Buy this book from NHBS.com
  • Seabirds

    by Peter Harrison - Helm 1985 ISBN: 071363510X Buy this book from NHBS.com
  • The Atlantic Gannet

    Bryan Nelson - Fenix Books Ltd 2nd Edition 2002
    See Farbirder Review ISBN: 095411910X Buy this book from NHBS.com
Organisations
  • Southern Oceans Seabird Study Association

    Website
    SOSSA was founded by members of the New South Wales Albatross Study Group (NSWASG) in 1994. It was set up to be an umbrella organisation for many study groups concerned with studies of Southern Ocean bio-diversity. SOSSA is a wildlife research and conservation group which consists of dedicated people both professional and amateur. These people share a common interest and concern for the environment and the wildlife of the Southern Oceans
  • The Seabird Group

    Website
    The Seabird Group, a registered charity, was founded in 1966 to promote and help coordinate the study and conservation of seabirds
Other Links
  • Seabird Osteology

    Website
    The Seabirds Skull Gallery, existing since 2002, has only been changed a bit and was given a new name that covers the subject more properly. After two years working on this site it is not only skulls anymore that are shown. Regular visitors have already noticed that since December 2004 the scope has widened. It now includes also other parts of the seabird skeleton. In the Seabird Osteology section general aspects of seabird osteology are treated and in the species section you willl find a listing of families and groups with links to pages on skeletons of particular species or groups. There is always work in progress, which means that there will be additions and improvements from time to timeā€¦
Photographers & Artists
  • Brown Booby Sula leucogaster

    Webpage
    Image
  • Nazca Booby Sula granti

    Gallery
    Images

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