Sulidae Totally Explained

Everything about Sulidae totally explained

The bird family Sulidae comprises the gannets and boobies. Both groups are medium-large coastal seabirds that plunge-dive for fish. The species in this family are often considered congeneric, placing all in the genus Sula. However, bones of Sula (boobies) and Morus (gannets) at least can in most cases be readily distinguished, and Abbot's Booby has traits of morphology and behavior not found in any other species and appears to be an ancient lineage maybe closer to the gannets than to the true boobies (Friesen et al. 2000).

Description

Sulids vary in length from 60 to 85 cm (23.5 to 33.5 inches) and in wingspan from 1.41 to 1.74 m (4.6 to 5.7 feet). They have long, narrow, angled wings and a rather long, graduated tail (the outer feathers are shorter than the central ones). Their flight muscles are rather small and their wing loading is high. Thus they must be streamlined, so their bodies are "torpedo-shaped", as well as somewhat flat (Nelson 2003).
Sulids have stout legs and webbed feet, with the web connecting all four toes. In some species the webs are brightly colored and used in displays. The bill is brightly colored, 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 are closed. The eyes are placed forward to provide binocular vision (Nelson 2003).
The plumage includes white underparts (light brown in some races of the Red-footed Booby and at least some dark brown or black above. Sulids have a preen gland whose waxy secretions they spread on their feathers for waterproofing and pest control. They molt during periods of relatively stress. They molt their tail feathers irregularly and the flight feathers of their wings in stages, so that starting at the first molt, they always have some old feathers, some new ones, and some partly grown ones (Nelson 2003).

Feeding

All species feed entirely at sea, mostly on fish and squid; some species follow fishing boats to scavenge on waste. Many species feed communally. The typical behavior is a dive from mid-air taking the bird a meter or two under water, after which it may swim with the legs and wings after its prey (Nelson 2003).

Reproduction

All sulids breed in colonies. Males examine the colony area in flight and then pick a nest site, which they defend by fighting and by territorial displays that derive from displaced aggression. Males then advertise to females by a special display and call. Females search the colony in flight and on foot for a mate. Once they select males, pairs maintain their bonds by preening each other and by frequent copulation (Nelson 2003).
The eggs are whitish, pale blue, green, or pink, unmarked till they become stained, and have a coating that resembles lime. Their weight ranges from 3.3 percent to 8 percent of the female's. Both sexes incubate; they don't have brood patches, but their feet become vascularized and hot, and the birds place the eggs under the webs. Eggs lost during the first half of incubation are replaced. Incubation lasts 42 to 55 days, depending on the species (Nelson 2003).
At hatching, parents move the eggs and then the hatchlings to the tops of their webs. they soon develop white down. They beg by touching the parent's bill and take food straight from its gape. After two weeks, both parents leave the nest unguarded at times while they obtain food. The times for the chicks to fledge and to become independent of their parents depend greatly on the species' food supply. Parents can't bring more than one chick to maturity except in the Peruvian Booby (which has the biggest clutches, two to four eggs) and occasionally in the Blue-footed Booby (Nelson 2003).

Systematics and evolution

The fossil record of sulids is quite extensive due to the many Miocene/Pliocene forms that have been recovered. The initial radiation formed a number of genera which are now completely extinct, such as the freshwater Masillastega or the bizarre Rhamphastosula which had a bill shaped like an Aracari's; at least the modern genus Sula is (like most genera of extant birds) documented from the Miocene onwards, with the doubtfully distinct Microsula being somewhat intermediate between boobies and gannets (Olson 1985). Family Sulidae

Genus Sula - boobies (6 living species, possibly 1 recently extinct)

Genus Papasula - Abbott's Booby

Genus Morus - gannets (3 species) Prehistoric sulids only known from fossils are:

Genus Masillastega (Middle Eocene of Messel, Germany)

Genus Eostega (Middle/Late Eocene of Cluj-Manastur, Romania)

Sulidae gen. et sp. indet. (Thalberg Late Oligocene of Germany: Darga et al. 1999)

Genus Empheresula (Late Oligocene of Gannat, France - Middle Miocene of Steinheimer Becken, Germany)

Genus Microsula (Late Oligocene of South Carolina, USA - Grund Middle Miocene of Austria) - doubtfully distinct; includes Pseudosula

Genus Sarmatosula (Middle Miocene of Credinţa, Romania)

Genus Miosula (Late Miocene of California)

Genus Palaeosula (Early Pliocene? of California)

Genus Rhamphastosula (Pisco Early Pliocene of SC Peru)

Sulidae gen. et sp. indet. (Late Piocene of Valle di Fine, Italy: Lambrecht 1933) Placement of "Sula" ronzoni (Early Oligocene of Ronzon, France) in the Sulidae is somewhat uncertain; it was initially described as a Mergus sea-duck, but this is incorrect. Later, it was proposed to be related to cormorants and the genus Prophalacrocorax was erected for it; this seems incorrect also (Olson 1985). For prehistoric species of the extant genera, see the genus articles.

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