An island breeder, the Brown Booby forages for fish and squid in surrounding waters by making plunge-dives, sometimes continuing to pursue prey underwater. The Brown Booby nests in colonies, with each pair defending a small area around their nest. While island breeding colonies are typically safe from most predators, falcons and ravens sometimes take young birds.
Most Brown Boobys don’t breed until age four, five, or six. While two eggs are often laid, only one chick usually survives. It is thought that boobys can live to be 30-50 years old, but adequate banding studies to confirm this are lacking.
Length: 30 in.
Wingspan: 57 in.
Photograph © Glenn Bartley
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Description of the Brown Booby
The Brown Booby is a seabird with long, narrow wings, a long, neck, and a long tail. It is brown above with a brown head and neck, white wing linings, and a white belly.
Male in breeding plumage has Grayish-green legs and feet, Bluish throat.
Yellow legs and feet.
Seasonal change in appearance
Juveniles have darker bellies and wing linings.
Fish, squid, and shrimp.
Forages by plunging head-first into the ocean.
Resident off south Florida and farther south, as well as off western Mexico.
Brown Boobies seldom raise more than one chick, unless food is exceptionally abundant.
Brown Boobies are skilled at soaring, and use air currents above the sea to stay aloft with minimal flapping.
Soft whistles and grunts are given on the breeding grounds.
The Blue-footed Booby has white in the upperparts and lacks the brown head and neck.
The nest is a shallow depression on the ground or a sea cliff.
Color: Whitish or blue-green.
Incubation and fledging:
– Young hatch at 40-47 days.
– Young fledge (leave the nest) at 84-119 days but remain with the adults for some time.
Bent Life History of the Brown Booby
Published by the Smithsonian Institution between the 1920s and the 1950s, the Bent life history series of monographs provide an often colorful description of the birds of North America. Arthur Cleveland Bent was the lead author for the series. The Bent series is a great resource and often includes quotes from early American Ornithologists, including Audubon, Townsend, Wilson, Sutton and many others.
Bent Life History for the Brown Booby – the common name and sub-species reflect the nomenclature in use at the time the description was written.
SULA LEUCOGASTRIS (Boddaert)
The common brown booby, or white-bellied booby, often called the brown gannet, is a widely distributed species among the islands of the tropical seas of both hemispheres. At the present time it is imown to be a North American bird merely as a straggler or an occasional visitor on our coasts, though its breeds abundantly at various localities in the West Indies.
Nesting: According to Audubon (1840) it formerly bred on one of the Dry Tortugas; I quote from his account of this colony as follows:
About eight miles to the northeast of the Tortugas Lighthouse lies a small sand bar a few acres in extent, called Booby Island on account of the number of birds of this species that resort to it during the breeding season, and to it we accordingly went. We found it not more than a few feet above the surface of the water, but covered with boobies, which lay basking In the sunshine and pluming themselves. Our attempt to land on the island before the birds should fly off proved futile, for before we were within fifty yards of it they had all betaken themselves to flight, and were dispersing In various directions.
The nest of the booby is placed on the top of a bush, at a height of from four to ten feet. It is large and fiat, formed of a few dry sticks, covered and matted, with sea weeds In great quantity. I have no doubt that they return to the same nest many years in succession and repair It as occasion requires. In all the nests which I examined only one egg was found, and as most of the birds were sitting and some of the eggs had the chick nearly ready for exclusion It is probable that these birds raise only a single young one, like the common gannet or solan goose.
This account of Audubon’s has been discredited by some modern writers, who think he must have been mistaken as to the owners of the nests, because this species is known to nest only on the ground and to lay two eggs instead of one. But, as Audubon studied the birds at close range and shot some 30 specimens, which he described and figured accurately, I see no reason for doubting his statement; moreover, Baird, Brewer, and Ridgway (1884) write that “Peale found it breeding on nearly all the coral islands visited” by the Wilkes exploring expedition, and that “the nests were constructed of sticks and weeds on bushes and low trees, and were generally found to contain but one egg.~~ The best modern account of the habits of the booby on its breeding grounds is by Dr. Frank M. Chapman (1908a). His studies were made on Cay Verde in the Bahamas, which he describes as follows:
Cay Verde lies on the eastern edge of the Columbus Bank, 30 mIles southeast of Little Ragged Island. It Is about 0.5 mIle long by 0.25 mile In greatest width, the longer axis lying approximately north and south, and, roughly esti. mated, contains some 40 acres. On the west and south, or shallow, bank sides there are steeply shelving beaches, where under favorable conditions a landing may be easily made. On the eastern side the deep blue waters of the ocean break directly against the characteristic water-worn limestone rock, of which Cay Verde, In common with other Bahama Islands, is composed. At the northern end, where the Islet terminates In a point, this rock Is but little above sea level. Southward It gradually Increases In height and, with pronounced Irregularities In coast line, reaches a blufflike elevation of 75 feet at the southeastern extremity of the islet.
About one-eighth of the surface of the island Is covered with a dense growth, chiefly of sea grape (Coccotobis uvif era), hut with a liberal mixture, mainly about the borders, of a “prickly-pear” cactus (Opuntia) and sea lavender (1’ouracfo,-tia gnepkatodes). Where sufficient soil has accumulated the remainder of the Island supports a growth of coarse grasses, sparse on the higher and rockier portions, more luxuriant In the lower portions, particularly about the margins of a small salt pond, the size of which was dependent upon conditions of tide and wind. There is no fresh water on the cay.
He remained on the island from April 9 to 11, 1907, and wrote a full account of his observations, from which I qilote in part:
A partial census of eggs and young led to the conclusion that there were about 1,500 pairs of boobies nesting on Cay Verde. They were distributed in several groups, where the comparatively level surface and sandy soil furnished favorable nesting conditions. In most instances the young were covered with down, with the brown second plumage more or less evident in wings and tail. A few birds of the year were already awing, and several nests contained fresh eggs. For the greater number of birds, however, the nesting season, as Bryant has stated, evidently begins in February.
The booby’s nests on Cay Verde were usually slight hollows in the ground, with often a scanty lining or rim of dried grasses, but in some Instances even this humble preparation for housekeeping was inciting, and the eggs were laid without pretence of nest.
About 98 per cent of the boobies nesting on Cay Verde had young, some of which were newly hatched, while a few were on the wing, but the largest number were beginning to acquire flight feathers. Of the nests, 35 contained eggs, of which 21 held 2 eggs, while in 14 there was but 1, but possibly In some, If not most, of these another egg would have been laid. As a rule, therefore, there were 2 eggs. this confirming previously recorded observations on the nesting habits of this species. On the other hand, 2 young were the exception. Of 740 nests counted by Doctor Mayer on the east side of the cay, only 2 contained young, and both pairs were well grown and approximately the same size.
Examination of the eggs contained In sets of two showed that either there was a marked difference In the development of the embryos or that one or both eggs were infertile. For example, of 13 nests containing 2 eggs, In 8 nests both were bad; in 10 both were good; but with every good pair there was about a week’s difference in the age of the embryo. In 6 nests, each containing one young and one egg, 5 of the eggs were decomposed.
With those bobbies which lay 2 eggs, apparently a week intervenes between the hying of the first and second egg, and to this unusual Irregularity, in connection with the high percentage of infertility, we attribute the discrepancy between the number of eggs laid and the number of young reared.
Dr. Alexander Wetmore has contributed the following notes on another interesting colony of this Species:
Off the ivest coast of Porto Rico, seven leagues from the port of Aguadilla, lies the small Island of Desecheo, hot and dry for a large part of the year, but swept occasionally by tempestuous dowapours of rain. The island is little xuore than an isolated rock rising from the restless waters of Mona passage with its treacherous changing currents, profound depths all about cutting It off from other land connection. In shape it is roughly an ellipse a mile and a half long and three-fourths of a mile wide with abrupt rocky shores and steep slopes rising into two pointed hills, the highest about three hundred feet above the sea. Three or four small Indentations boast a rough gravelly beach where with care a landing can be made In the surf and behind these are small semicircies backed by water-worn cliffs on the laudward side and floored with sand and huge rocks fallen from the overhang above. The thin soil of the island supports a considerable growth of vegetation, bound with thorny creepers Into an Impassable jungle, with only small grass-grown openings offering a pathway. The West Indian birch (BurserG 8imaruba), with its trunk and limbs curiously shortened, thickened and gnarled in the struggle for life, Is the common tree, while growths of three species of cactuses are common.
On this interesting island, boasting of but eleven resident avine forms, the booby (Su~a leucoga8tra) has chosen its home and here In June, 1912, I spent a few days in studying the habits of these ungainly birds. Between eight and ten thousand of them at a conservative estimate occupied the rookeries, spread over the entire island, hut they were so distributed on the steep brush-covered slopes that a more accurate census was Impracticable. Though they were seen at the top of the higher of the two hills, the greater number were found within four hundred feet of the beach, gathered usually in groups. By my fishermen they were said to nest from late June until October, but these dates are very uncertain. The young now were nearly all caring for themselves, though a few showed traces of down feathers clinging to the tips of the feathers about the head, and I would consider February or March a more probable date for their nesting. A few were seen playing with sticks and straws as though contemplating nest building, but the sexual organs of those taken were little developed. Birds in all po~sible intermediate plumages were seen and immature specimens were much more common than the fully adult with smooth dark brown heads and white underparts.
The young birds were averse to flying when they could avoid it, but preferred to scramble away under the bushes awkwardly, falling over sticks and stones in their haste. Even the adults could not take flight from a level surface, but had to launch themselves from the cliffs and sail down for a distance before being able to rise with strong wing beats. From the limbs of the trees they flew readily, but on the ground I captured several by merely pinning them down with my gun barrel. They showed little real fear of me and many stood their ground, snapping and hissing, and it was a point of wisdom to keep beyond reach of their sharp powerful beaks. It rather gave me the shivers occasionally to see one flounder and flop through and over a bed of prickly pear, but the birds seemed careless of the thorns. Numbers were seen with spines or even small lobes of cactus hanging to the feet or wings, and the dissemination of the plants by this means can be readily pictured. At a gunshot there was a great rush among those near by, and the air for a few minutes would be filled with them circling and crossing, frequently almost within reach. The confusion among theni would cease gradually, and they would soon be all around again, eyeing me curiously or forgetful of my presence, busy with their own affairs. On the rough limestone blocks above the sea they sat in rows in the blazing sun, rather upright, occasionally waddling along a foot or two, but usually motionless. Birds came and went during the day, flying out to sea to feed, sometimes at considerable distances off shore, but they were most active in the morning and evening. The common call note was a loud quack quack quack, and at night, whenever I awoke, there was always much commotion among them.
Eggs: From the foregoing quotations it would seem as if two eggs was the normal set with the common booby, but apparently sometimes only one is laid. The eggs vary considerably in shape and size, but usually they are elliptical ovate, elongate ovate, or elliptical oval. The underlying color of the shell is pale bluish white, but it is usually completely or nearly covered with a thin layer of white calcareous deposit. In some eggs this deposit is uneven, broken, or rough, but usually it has a smooth, clean, lustreless surface.
The measurements of 40 eggs, in the United States National Museum and the writer’s collections, average 59.4 by 40.2 millimeters; the eggs showing the four extremes measure 65.5 by 41, 62 by 42.5, 52.5 by 40, and 56.5 by 34.5 millimeters.
The male assists the female in the duties of incubation, but the period of incubation seems to be unknown. The behavior of the birds during the incubating and brooding period is fully described by Doctor Chapman (1908a) as follows:
One or both of the adults remain, as a rule, with the young. On March 9 the birds awoke at 5.15 a in., when for the ensuing 10 or 15 minutes there was a subdued kind of quacking, and some birds were seen flying. At 5.30 several hundred birds left the rookery in a body to go a-fishing, this being the first general movement. Individuals returned at Intervals during the day and evidently changed places with the bird left at the nest, which In turn xvent out to feed and to gather fish for the young. There was no concerted return movement until dusk, when flocks of birds came In from the sea, the last comers not arriving until after dark. In the meantime the man-o’-war birds had retired, and it i~ not impossible that the boobies have acquired the habit of “staying out late” to avoid being robbed of their food by the man-o’-war birds, which at times attacked them as they approached the cay and forced them to disgorge.
Sitting or brooding birds spend the night upon the nest with the mates standing at their sides, but the close resemblance of the sexes rendered it impossible to distinguish them at this time. When the young is too large to be brooded, It passes the night on the ground between the two parents, which stand on either side, all three with their heads tucked under their scapulars.
When perched on rocks about the border of the island, boobies showed a decided fear of man and generally flew before one had approached to within 30 yards of them; hut when on their nests they were conspicuously tame, the degree of tameness being related to the advance of the nesting season. A bird with newly hatched young would not, as a rule, leave the nest unless actually forced to do so, and it would strike so viciously at anyone approaching that it was well not to venture ~vitbin its reach. This was the extreme development of parental instinct, which now gradually diminished as the young increased In size. Evidently as a result of excitement caused by our presence, the birds which remained to defend their young threatened us with their bills, picked up bits of sticks or grasses only to drop them and pick them up again, and even struck at their own young in a confused and aimless manner. The young also had this habit. The report of a gun occasioned but little alarm among the boobies, some of which, with their young near my feet, did not fly when the gun was discharged.
In spite of the apparent sociability expressed by their communal habits, the boobies immediately resented trespass on their home site by one of their own kind. Where the nature of the ground permitted, their nests were placed with more or less regularity 6 to 8 feet from one another. As long as a bird re-inained within its own domain, having a diameter of approximately 6 to 8 feet, it was not molested; but let it or its young advance beyond these lijuits and they were promptly attacked.
So closely, however, lire the birds confined to their own little areas that difficulties of this kind are rare, antI under normal conditions peace reigns in the rookery. But when, as we walked through the rookery, the birds, in escaping from the larger evil, forgot the lesser one and inadvertently backed onto a neighbors’ territory, the unusual cause of tile trespass was not accepted as an excuse and they found the frying-pan ” worse than the lire,” as tile enraged owner, with bristling feathers, furiously assailed them with open bill, sometimes taking hold. At these tinies and whenever the birds were alarmed, they gave utterance to hoarse, raucous screams or screeches, though as a rule they xvere comparatively silent.
Young: Regarding the young birds he says:
The young booby Is horn practically naked, and since exposure to tile sun before the downy plumage is developed would result fatally, it is constantly brooded, one parent iluuluiediately replacing the other when the brooding bird is relieved. Brooding continues even when the white down is well developed and the young bird, then too large to be wholly coveied by the parent, lies flat Ofl tile ground, the head exposed, the eyes closed, apparently dead. This relaxed attitude is also taken by young ~vhich are not sheltered by the parent, and we were not a little surprised on several occasions ~~’iuen about to examine an evidently dead bird to have it jump up, and with a trumpeting call, blare at us ~x’ith opeii mouth. Nor do they rely only on tile voice for defense, but nsa the bill effectively, and, as has been remarked, they possess with the adult, the somewhat ludicrous habit of venting their feelings by picking up hits of stick and grass.
Compared with other rookeries I have visited, tile niortahity among young boobies on Cay Verde: aside from the prenatal niol-tality already referred to: was surprisingly small. Tills I attribute to the isolation of the cay, which permits the birds to rear their young with little or no intrusion by man, whose presence, even as a visitor, results in great confusion and consequent death among the young of ground-nesting colonial birds.
The young were fed on squids and fishes, which, in a more or less digested condition, they obtained by thrusting their heads and necks down the parent’s throat, a manner of feeding common to all the Steganopodes ~vith whose habits I am familiar (inchudiiig Pclecaaas, Fregata, Plomlocrocorax, and Anltfnga). I have not, however, seen Phecihon feeding its young, and it would be interesting to know whether this tern-like Inember of the order has a sinuilar method of administering food.
Evidently but omie brood is reared, since approximately three months must elapse after the egg is laid before the young can fly am)d care for itself.
Plumages: The yotlng booby is hatched naked, hilt the down soon begins to sprout in the various feather tracts and shortly clothes the whole body, heati, and neck, except. the naked face, with a ptire white, soft, woolly covering. rrhe juvenal, or first real plumage, appears first on the wings, the primaries coming first; the tail soon follows, so that all the flight feathers are developed at an early age and considerably in advance of the body plumage; the latter appeal’s first on the breast. Doctor Chapman (19O8~) describes the juvenal plumage as follows:
In the succeeding specimen the second or juvenal plumage is essentially coalplete, except upon the foreneck, where it is just emerging. This bird Is almost uniform grayish-brown above; the upper tall coverts are slightly browner; the exposed portion of the remiges and rectrices show a somewhat frosted effect; the primaries are decidedly blackish; the lower breast and abdomen are grayer than the dorsal plumage; the upper breast (with which the throat feathers would apparently agree) Is decidedly browner.
This plumage is apparently worn for about a year or until the first complete poatnuptial molt. I have seen young birds in this wholly brown plumage in July, September, January, and March and have seen birds molting out of this plumage and into the whitebellied adult plumage in May, in July, and in September. Young birds therefore probably become indistinguishable from adults wheii about a year and a half old.
The small amount of material available for study makes it difficult to arrive at any satisfactory conclusions as to the sequence of plumages and molts of this species. I have seen but one adult in full molt; this is a July bird in which the primaries are in such condition that the bird must have been practically incapable of flight.
Food: The food of the booby consists almost entirely of fish, chiefly flying fish and mullets, many of them of large size, which it is very expert in catching by diving. Audubon (1840) says:
The expansIbility of the gullet of this species enables it to swallow fishes of considerable size, and on such occasions their mouth seems to spread to an unusual width. In the throats of several Individuals that were shot as they were returning to their nests, I found mullets measuring seven or eight Inches, that must have weighed fully half a pound.
Mr. Austin H. Clark (1903), writing of the habits of this species on the Venezuela coast, says:
They seemed to approach the land solely for the purpose of feeding, after which they withdrew to open water. Just off Carfipano there was a certain spot to which every day came hundreds of sea birds of many species to fish. Over one-half of this congregation were common brown pelicans and most of the rest were these gannets. Overhead soared a score or more frigate birds, while various gulls and terns composed the remainder. All the larger members of this vast flock acted in perfect unison, wheeling about until a sufficient altitude was obtained, all diving with a great splash, then all slowly rising again to repeat the performance.
Single boobies may often be seen fishing in company with solitary pelicans, imitatIng In every way the actions of their larger companions, diving at the same time, and rising simultaneously. Mr. Outram Bangs has suggested to me that perhaps the booby, being smaller and more active, finds a good fare in the fish which the uncouth pelican fails to catch.
Dr. Henry Bryant (1861) says of its feeding habits:
The booby is, I think, the most expert diver that I am acquainted with; no matter in what position It may be, whether flying in a straight line, sailing in a circle, just rising from the water, or swimming on the surface, the instant it sees its prey it plunges after it. I have frequently seen one dive from the wing, rise to the surface, and dive in rapid succession five or six times; and on taking flight again, dive before it bad risen more than two or three feet from the surface, and perhaps catch a dozen fish in the space of a minute.
There is nothing graceful in its style; it is apparently work and not pleasure. On one of the keys I visited, called Booby Key, near Green Key, I saw a great number of a species of Ano its of a dark, almost black color, entirely unlike any seen elsexvhere, but they were so timid and active in their movements that I could not procure a specimen. The stomach contained a great many varieties of fish; among them a cottus. a parrot fish, fiatfish of two species, and some large prawns; but their principal food seemed to be flying fish and a species of hemirhamphus.
Behavior: Audubon (1840) describes its flight, as follows:
The flight of the booby is graceful and extremely protracted. They pass swiftly at a height of from twenty yards to a foot or two from the surface, often following the troughs of the waves to a considerable distance, their wings extended at right angles to the body; then, without any apparent effort, raising themselves and alloxving the rolling waters to break beneath them, when they tack about, and sweep along in a contrary direction in search of food, much in the manner of the true petrels. Now, if you follow an Individual, you see that it suddenly stops short, plunges headlong into the water, pierces with its powerful beak and secures a fish, emerges again with inconceivable case, after a short interval rises on wing, performs a few wide circilugs, and makes off toxvard some shore. At this time its flight is different, being performed by fiappings for twenty or thirty paces, with alternate sailings of more than double that space. When overloaded with food they alight on the water, where, if undisturbed, they appear to remain for hours at a time, probably until digestion has afforded them relief.
The booby is usually a silent bird, but when excited it is said to utter loud and raucous cries which have been likened by various observers to the croak of a raven, the honk of a goose, or the hoarse quack of a duck.
Undoubtedly the booby’s worst enemy is the man-o-war bird, to which it pays frequent and regular tribute, but Audubon (1840) says: “Their principal enemies during the breeding. season are the American crow and the fish crow, both of which destroy their eggs, and the turkey buzzard, which devours their young while yet unfledged.”
Winter: After the young birds are able to fly the boobies leave their breeding grounds and begin their fall and winter wanderings up and down the coasts, following the schoois of fish, on whioh they feed. These wanderings, which can hardly be called migrations, sometimes take them as far north as Massachusetts.
Breeding range: The Bahama Islands (Cay Verde, San Domingo Key, Berry Islands, etc.) ; some of the West Indies (Porto Rico, Jamaica, St. Thomas, Dominica, St. Vincent, Battowia, etc.) ; the Cayman Islands; off the coasts of Venezuela (Los Testigos and Los Hermanos Islands), Honduras (Belize and Swan Islands). Costa Rica (Uvita Island), and Brazil (San Paulo and Fernando Noronha); and in the tropical Atlantic Ocean (St. Paul Rocks and Ascension Island). Birds which breed on islands in the western Pacific and the Indian Oceans are probably subspecifically distinct. Breeding grounds protected on Desecheo Island reservation, Porto Rico.
Winter range: The Caribbean Sea, Gulf of Mexico, and Atlantic Ocean, from the Bahamas and Florida south to the Straits of Magellan and Ascension Island.
Casual records: Has wandered to Massachusetts (Cape Cod, September 17, 1878), Bermuda (October 3, 1847, and September 26, 1875), and Louisiana (below New Orleans, two taken in September, 1884).
Egg dates: Bahama Islands: Sixteen records, January 14 to June 12; eight records, April 15 to May 19.