56 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I50 



2. Plain sooty brown above, and on throat and upper breast, the latter sep- 



arated posteriorly from the white or grayish brown lower breast by a 



definite line Brown booby, Sula leucogaster, p. 56 



White above, or grayish brown, variegated with white 3 



3. Tail black Blue-faced booby, Sula dactylatra, p. 60 



Tail grayish, or grayish and white Blue- footed booby, Sula nebouxii, p. 61 



SULA LEUCOGASTER (Boddaert): Brown Booby; Piquero Moreno 



Figure 11 



Adult with neck and upper breast dark, set off sharply from the 

 white of the rest of the under parts. 



Description. — Length 660 to 760 mm. Adult, brownish black, with 

 the lower breast and abdomen white. 



Immature, dark grayish brown, with the under surface paler, 

 somewhat mottled, usually with a faint indication of the sharply 

 defined line that in the adult separates the white and dark areas of 

 the breast. 



Brown boobies, found along both coasts, are more abundant in 

 the Gulf of Panama than in the Caribbean. To see them it is neces- 

 sary usually to go offshore, though occasionally they come along the 

 mainland, around rocky headlands, or at the heads of bays. Over 

 the Gulf of Panama they appear regularly as single birds or small 

 groups that course with set wings, low near the water shifting at 

 intervals in the air currents to rise 10 to 15 meters above the surface. 

 Angular in form, they are streamlined gliders from the tip of the 

 sharp-pointed bill, back over its swelling base and the increasing 

 diameter of the head and the thickened neck, with no appreciable 

 break in outline. This smooth contour swells over the body, and then 

 tapers to termination in the long, pointed tail. The narrow wings, 

 held stiffly without flapping at right angles to the body, are the 

 efficient sail-planes that support the bird, and through slight shifts in 

 angle guide its course and regulate its speed. Only in take-off from 

 the water, or from a perch on land does the booby stroke its wings, 

 and then only to gain sufficient momentum for support on the air 

 currents over which it rides. 



Brown boobies live mainly around small offshore islands, on some 

 of which they nest. They rest usually on the face or summits of 

 cliffs or on jumbled rocks above the shore. When the air is calm 

 they remain inactive, but when the wind freshens they range out to 

 feed. In travel by launch through the waters that they frequent one 

 often sees boobies swing briefly near at hand and then, their 

 curiosity satisfied, veer off, intent on their fishing. It is mainly the 

 immature birds that show continued interest, and follow boats for 



