The family Sulidae (collectively called "sulids") consists of three genera of strictly marine and primarily pelagic seabirds: Morus (gannets; four species worldwide, only one occurring in the Northern Hemisphere), Sula (boobies; 5 species worldwide with primarily Pantropical distribution), and Papasula (Abbott's Booby; endemic to Christmas Island in the Indian Ocean). All sulids are characterized by a long, dagger-like, conical bill (slightly more hooked on Abbott's Booby), long pointed wings, and long wedge-shaped tails. Sulids fly with several deliberate strokes followed by a glide. All species are superb plunge divers, often beginning their dive from great heights. When a bird sights its fish prey, it gains height above the water, then folds its wings close to its body, and falls like a dart towards the surface of the water, often at an angle. If captured, fish are consumed under or at the surface of the water. Sulids search for schools of small fish, or are drawn to their prey by the sight of other feeding birds, marine mammals, or large fish (like tuna). Their characteristic flight silhouette (reminiscent of a slender, long-winged pelican or heavy-bodied shearwater) can be detected from long distances. All species are essentially pelagic, coming ashore only to nest or roost. All species, except Red-footed, are primarily diurnal feeders, returning to roost at the breeding colony, or on some offshore substrate: platform, or ship rigging, or some flotsum. Masked Boobies have been reported to rest on the backs of sea turtles. Red-footed Booby is reported to feed at dusk and even through the night. Northern Gannets often roost on the water during the non-breeding season. All species have a distinct juvenal plumage and require two or more years, and a number of transitional plumage types (age/plumage sequence of many species remains unclear), to attain definitive (full adult) plumage. Adult breeding and non-breeding plumages are identical. The coloration of the soft parts (bill, facial and gular skin, legs and feet) intensifies in anticipation of the breeding season. One species, Red-footed Booby, is polymorphic. Two distinct morphs (and intermediates) characterize this species' definitive plumage. The main character separating gannets from boobies is the shape of the bare skin in the gular (throat) area. The gular skin of gannets extends from the base of the bill in a narrow strip, extending down the throat and terminating in a point. In contrast, the bare gular skin pattern of boobies is squared-off along the bottom of the throat, similar to the pattern found on cormorants. This distinction between gular patterns can easily be seen at close range.

Status and distribution. Of the four species of sulids thus far documented for Louisiana, only two are detected with any reliability. The Northern Gannet (Morus bassanus) breeds spring through summer on sea cliffs in the North Atlantic. Birds winter within the breeding range, as well as move south along both coasts, mostly over the continental shelf, reaching the Gulf of Mexico and the coast of north Africa. Northern Gannet is the most plentiful sulid in Louisiana, and is the expected species to be observed from or on shore. It has become an uncommon to fairly common winter resident on Louisiana's offshore "green" waters and can regularly be seen from coastal vantages of the open Gulf. It is less common in the brown waters of the Mississippi River plume, but is regularly observed from shore off Cameron Parish. The species' peak occurrence is between early November and late April, which coincides with the species' non-breeding season. A few individuals (sub-adults or sickly birds) attempt to summer on the Gulf, and stragglers are occasionally encountered on Louisiana's beaches. This species is regularly attracted to bird activity behind trawlers.

Unlike the gannet, the Masked Booby (Sula dactylatra) is a strictly a "blue water" species. Masked Booby ranges throughout all tropical oceans. Louisiana records involve the nominate subspecies (S. d. dactylatra), which breeds (seasonality not well-defined, more often fall through spring) in the Caribbean, on the Cayman Islands, Jamaica, off Puerto Rico, the Virgin Islands, and Lesser Antilles. Non- breeding birds range at sea within the breeding area as well as move north into the Gulf of Mexico. Most Louisiana records are from July to late October. Because blue water is usually far off the Louisiana coast, the chances of seeing a healthy, non-storm related Masked Booby from shore is slim. Masked Boobies can be adversely affected by tropical storms and hurricanes. Occasionally, windblown birds may be found on shore following these storms (often dead or moribund), or even driven far inland depending on the ferocity of the storm. The farthest inland this species has been recorded in Louisiana is East Feliciana Par., courtesy of Hurricane Carla. Masked Boobies have been reliably found on LOS and other pelagic trips to deep water, where they are seen roosting on buoys or oil platforms, or feeding over fish schools (such as anchovies and flying fish). Masked Boobies often investigate boats and will often circle several times checking for potential meals (chum or fish "flushed" by the boat). Currently on the LBRC Review List, recent work offshore is revealing that this species is regular and removal from the Review List may be warranted.

Brown Booby (Sula leucogaster) is another Pantropical species. Louisiana records pertain to the nominate subspecies, S. l. leucogaster, which breeds in the southern Atlantic and in the Caribbean off Yucatan, the Bahamas, and south to the Antilles. This is another Review List species, with only six confirmed or LBRC-accepted records for the state. Texas currently accepts six records (including two winter records). This species is likely more numerous in the northwestern Gulf of Mexico than current records from Louisiana and Texas would indicate. The records span April through mid-October. As with Masked, this booby can be attracted to and will follow boats. It is only a matter of time before one is located on a LOS Pelagic Trip! Because this species prefers deep blue water, it is not likely to be encountered on or near shore, unless driven there by a tropical storm or sickness.

Red-footed Booby (Sula sula) also has a Pantropical distribution. The nominate subspecies nests in the Carribean off Yucatan, Belize, the Cayman Islands, the Bahamas, Puerto Rico, the Virgin Islands, and the Grenadines. It primarily ranges within the breeding area during the non-breeding season. It is the rarest sulid in the northwestern Gulf of Mexico and is on the Review List. There is only one currently accepted Louisiana record, a specimen of a juvenile collected at the mouth of Bayou Scofield, Plaquemines Par. on 1 November 1940. Two recent reports are pending LBRC review. It has only been recorded once off Texas (March 1983). Red-footed Booby is also a blue water species. It is reported to be more "sedentary" than Brown and Masked boobies, which may account for the paucity of records. Wouldn't a Red-footed be a real treat on a LOS trip?

No other species of sulid is expected (as a natural vagrant) to occur on Louisiana waters. Blue- footed Booby (Sula nebouxii), a Pacific Coast species, breeding on islands off Mexico, Ecuador, and northern Peru and the Galapagos Islands, has occurred twice in the interior of Texas, records that may have been associated with tropical storms (driving the birds well inland) or human intervention (boobies are exceptionally tame compared to other birds). Several reports of this species from Louisiana either remain unsubstantiated or have proven to be either Northern Gannets or Masked Boobies.

Identification. Sulid identification is not too difficult with respect to the four species that have occurred in Louisiana (we will focus only on these four). The main characters used in identification are: size and plumage color/patterns (notably color of head, upper wing and under wing coverts, secondaries, tail, and rump). To put size into some perspective, compare size of the large Northern Gannet (slightly smaller wingspan than a Brown Pelican) to the medium-sized Masked and Brown boobies (wingspan slightly larger than a Herring Gull or a Double-crested Cormorant), to the small Red-footed Booby (approximately the wingspan of a Laughing Gull or Neotropic Cormorant). Remember that size of individual birds can be difficult to judge - use nearby species as a reference. Soft part colors (bill, facial and gular skin, legs and feet) may be useful for field identification, but are not easily observed under most field conditions.

Northern Gannet is separated from boobies in any plumage by its larger size and the shape of the gular patch. The facial skin and gular "stripe" are dark gray. Unlike the uniform-colored legs and feet of boobies, those of the Northern Gannet have a two-tone coloration formed by a stripe running the length of the tarsus and out each toe. These "racing stripes" are chartreuse and are usually prominent on the otherwise dark gray background. These three features make separation of gannet versus booby straightforward at close range. Identification of sulid species in Louisiana should always start with elimination of Northern Gannet. This species has been confused with Masked, Brown, and even Blue- footed boobies!

A Northern Gannet takes 4-5 years (prehaps longer) to attain definitive basic plumage. The juvenal plumage is sooty brown above, speckled with small white dots (visible only at close range). The chest is somewhat darker than the remainder of the underparts, each feather with spots or finely edged with white, imparting a mottled appearance on very close inspection. The uniform underwing linings are somewhat paler than the underparts. The flight feathers and tail are brownish-black. The rump has a pale diagnostic "U." The bill is dark gray and the eye is bluish-gray. Birds at a great distance look essentially all dark. Through subsequent molts, the juvenal coloration is replaced with portions of the black and white adult plumage. Sub-adult plumages are quite variable. Feather wear may also alter the otherwise dark plumage, bleaching flight and tail feathers to a pale brown. The diagnostic pale "U" remains through subsequent plumages. The "whitening" process progresses on the underparts, upperwing coverts, tail, and secondaries. Sub-adult Northern Gannets in black-and-white transitional plumage stages can be distinguished from all boobies by possession of a few to many white secondaries or black and white tail feathers. The Northern Gannet in full adult plumage is a dazzling sight with a golden head, black primaries and primary coverts, and the rest of the plumage is entirely snow white, including all of the secondaries. No other species shares this combination of plumage characters.

The Masked Booby is one of the two "medium-sized" boobies, but much smaller than a Northern Gannet. Like the gannet, it has a black and white definitive plumage, but differs in the greater extent of black on the wing (includes all of the secondaries), entirely black tail, and lacks the golden cast to the head. The black tail further separates it from definitive white morph Red-footed Booby. Its old name, "Blue-faced" Booby, focused on its deep grayish-blue facial skin and gular patch as a distinguishing feature from the other species of boobies. Its legs and feet vary from yellow (adults) to dull olive to bluish- gray (sub-adults; no doubt responsible for some reports of Blue-footed Booby) to black (juveniles). The bill is generally light-colored, ranging from a dull yellow (adults) to light slate gray (juveniles). Masked Booby takes 2-3 years (possibly longer) to attain full adult plumage.

Juvenal-plumaged Masked Booby is uniform dark brown above, broken by a whitish collar, and is entirely white below. (But beware, the white underparts may become soiled with oil; one bird salvaged off the coast is entirely brown below and could potentially be confused with a Brown Booby if not for noting other Masked Booby characters!) The flight and tail feathers are blackish-brown. The feathers of the upperparts have small white edges, the broadest edges in the upper mantle. These edges further highlight the pale collar. The underwing linings are white, contrasting with the dark primaries and secondaries, and are bisected lengthwise with a dark brown bar. The overall appearance of juvenile Masked Booby is quite unique. Only Brown Booby (in definitive plumage) shows a similar stark brown and white plumage pattern, but differs from Masked, by its dark brown neck and chest and uniformly dark brown upperparts. Transitional plumages of Masked Booby gain more white, most apparent on the head, back, and upper wing coverts. During the Masked Booby's transitional sub-adult plumage, when essentially "black-and-white" it can be confused with a sub-adult gannet. Most gannets, even those still with entirely black secondaries, will show some gold color on the head or some white tail feathers, but if these gannet-features are missing, Masked Booby differs by its smaller size, as well as having an entirely black face and gular pouch and dull yellow bill. The "Nazca Booby" recently highlighted in FieldNotes is a Pacific Ocean form, not likely to occur in Louisiana waters.

Like Masked, Brown Booby is a medium-sized booby. The adult in definitive plumage is dark brown above, including the head and chest. The remainder of the underparts are white. White extends on the underwing linings and is encircled by brown on the leading and trailing edges of the wing and the brown primaries and their coverts. Bill color is variable, but is generally greenish-yellow blending towards a grayer tip. Facial skin color is also variable, generally aqua around the eye blending to gray with a greenish-yellow gular pouch. The eyes at all ages are whitish. The legs and feet are generally orangish- yellow or dull greenish-yellow. Brown Boobies acquire their full adult plumage in 2-3 years. The juvenal plumage shares the definitive pattern, but the white is replaced with a pale brown. The underparts "whiten" through subsequent molts. Brown Boobies are fairly easy to identify in definitive plumage, only the Masked Booby is similar (see above). The juvenal-plumaged Brown Booby is most most similar to the juvenal-plumaged Red-footed Booby. This represents the greatest identification challenge among Louisiana's sulids, especially to those observers not familiar with size and proportions of the two species. Red-footed is the smaller, more delicate, slender-winged, and longer-tailed of the two species, and with ample experience, these characters should facilitate identification. Although most immature Brown Boobies are distinguishable by the shadow appearance of the definitive plumage (dark head and chest divided from somewhat paler underparts), some Red-footeds may show a similar pattern. The best distinguishing character for birds in juvenal plumage is the more uniformly dark underwing linings of Red-footed Booby. Brown Booby wing linings are paler, nearly concolor (or lighter) with the belly. Red-footed Booby often has pale tips to the tail feathers, but this would be difficult to confirm without close inspection, as to eliminate wear as a possible cause of such coloration. Leg color is not a reliable feature, as many young Red-footeds may have yellow or yellowish-orange legs and feet, that look essentially the same in the field as the flesh, or orange-flesh legs of the juvenal Brown. Also beware the feet of a Brown Booby can look much "redder" when back-lit.

The Red-footed Booby is the smallest species. Red-footeds are slighter in overall proportions than the other species, possess a more shearwater-like flight, and have a bill with a somewhat more hooked-tip (visible only at very close range). Unlike the other species, it is polymorphic. There are two main adult plumage types: 1) white morph with white tail (black tail on Galapagos); and 2) brown morph with white rump and tail (occasionally all brown). Intermediate plumages also occur. The adult white morph is characterized by black primaries, secondaries, and black carpal patch on the primary coverts of the underwing, contrasting with an otherwise all white plumage, including the tail; the head is tinged with gold. No other species shows this combination of characteristics. The brown morph is quite different. The head and underparts are uniformly grayish brown, the mantle somewhat darker, and set off from the white belly, rump, and tail. No other sulid species possesses a uniformly dark body and a white tail. Caribbean birds are generally white morph; the brown morph being fairly rare. All adults have bright red legs and feet. The bill (non-breeding condition) is light bluish-gray, pink at the base; this color also extends across the forehead. The facial skin is a combination of blues and pinks. Iris is apparently dark in Caribbean birds. Red-footeds is superficially similar to the larger and bulkier Masked in the black and white plumage, but lacks the black tail (except Galapagos form). Like the other boobies, Red-footeds attain their adult plumage in 2-3 years. The juvenal-plumaged Red-footed Booby is all dark brown, slightly paler below with a faint, but slightly darker chest band. The bill is dark gray, facial skin purplish-gray. Adult brown morph brown- tailed individuals are similar to juveniles, but have adult soft part colors and a golden cast to the head. Plumage transition from juvenal to adult plumage depends on the morph type, but is a gradual "whitening" either just the rump/tail or the entire upperparts. In the latter case, it is similar to the progression of Masked Booby. The juvenal plumage is most similar to Brown Booby (already discussed) but could also be confused with a gannet, if not for the incredible size difference. Both birds are essentially all dark. The Red-footed Booby is tiny compared to a gannet, and has unicolored yellow or orange legs and feet and a dark bill, and lacks the white speckling and "U" rump patch characteristic of the young gannet. Despite their relatively small size, Red-footed Boobies could be confused with various other species. The sub-adult gannet could potentially be confused with a white morph adult Red-footed Booby; white morph Red-footed Booby has an all white plumage, except for black primaries and secondaries. Red-footed Booby is much smaller and has a diagnostic black carpal patch similar to that of a White-tailed Kite. If a mystery bird is essentially "black and white," then note the color of the following: head, secondaries, tail, underwing coverts. The best distinguishing character between sub-adult Masked and Red-footed boobies is size and the color of the tail. It is important to be familiar with these distinctions so as to be prepared in the case of a chance encounter.

---Donna L. Dittmann and Steven W. Cardiff, LSU Museum of Natural Science