Sulidae Boobies and Gannets
Version: 1.0 — Published March 4, 2020
Introduction
Their comical courtship displays, showing off brightly colored feet to potential mates, together with their resolute attendance of their nests and relative slowness on land, gave boobies their name. But at sea, where they spend most of their lives, the sulids are most impressive predators. Scissoring their long wings behind them, they plunge from great heights in pursuit of schooling fish near the surface, slicing down into the water at speeds over 100 km per hour. It is thus no accident that they lack external nostrils. Sitting in a small boat among a flock of boobies or gannets sizzling into the water is one of the most exciting experiences an ornithologist can have.
Habitat
Gannets and boobies are primarily pelagic during most of the year, although they usually do not range far beyond the continental shelf. Sulids typically nest on small offshore islands away from mammalian predators.
Diet and Foraging
Gannets and boobies feed on a wide variety of fish and squid. Sulids have a spectacular method for catching prey, often diving from as high as 100 m above the water. When diving, they are truly torpedo-like, pulling back their wings into a streamlined configuration that allows them to plunge to 10 m, followed by further pursuit of their prey underwater up to depths of 25 m. This foraging strategy allows sulids to exploit large shoals of energy-rich fish that are off limits to other birds.
Breeding
Sulids are monogamous, many with long-lasting pair bonds and biparental care. Their highly developed courtship displays often emphasize brightly colored feet. Nesting substrates vary among species, ranging from flat or steeply sloping ground to cliffs and trees. Most ground-nesting boobies make simple scrapes whereas gannets build mounded cones of seaweed, grasses, and feathers, which are cemented with guano. Red-footed Booby Sula sula and Abbott’s Booby Papasula abbotti build simple stick nests in trees. Clutch size varies from 1 to 3, with the gannets laying only a single egg, Blue-footed Booby S. nebouxii and Peruvian Booby S. variegata regularly laying up to 3, and the other boobies laying 1 or 2. Both members of a pair participate in all aspects of parental care, including incubation, brooding of chicks, and provisioning of young. Incubation takes 41 to 45 days (up to 57 days in Papasula), and the chicks fledge after about 2.5 months of feeding (5 months in Papasula). The can be fed by their parents occasionally up to nine months postfledging.
Conservation Status
Two species of sulids (20%) are at risk (1 VU, 1 EN). The endangered Abbott’s Booby Papasula abbotti is restricted to Christmas Island, where it is rapidly declining due to habitat destruction, hunting, and introduced mammalian predators.
Systematics History
Sulidae has traditionally been considered part of the order Pelecaniformes, but more recent morphological and molecular studies have found it to be sister to the clade formed by Phalacrocoracidae and Anhingidae (Livezey & Zusi 2001, Ericson et al. 2006a, Hackett et al. 2008). These families together are sister to Fregatidae (Livezey & Zusi 2001, Ericson et al. 2006a, Hackett et al. 2008), forming the group that we recognize as Suliformes.
Conservation Status
Least Concern |
80%
|
---|---|
Near Threatened |
0%
|
Vulnerable |
0%
|
Endangered |
20%
|
Critically Endangered |
0%
|
Extinct in the Wild |
0%
|
Extinct |
0%
|
Not Evaluated |
0%
|
Data Deficient |
0%
|
Unknown |
0%
|
Data provided by IUCN (2023) Red List. More information