210 BULLETIN 121, UNITED STATES NATIONAL MUSEUM. 



Dr. E. W. Nelson (1899) describes a breeding colony of this species 

 as follows : 



Only a few of these boobies were seen about the Tres Marias until an islet 

 was visited off the northwest shore of Maria Cleofa. This islet rises from 150 

 to 200 feet above the sea, with cliffs on all sides. The summit is mainly rollinjr, 

 with an elevated, sloping bench on one end. At this time, May 30, many 

 thousands of boobies were breeding on the bare top of this rock. Ths eggs 

 were laid directly on the surface, with no sign of a nest. The sun was in- 

 tensely hot and heated the rocks so that they were uncomfortably warm to 

 the touch. The birds did not sit upon the eggs during the hottest hours, but 

 while standing to avoid contact with the heated rocks kept in such position 

 that the eggs or young were shaded from the sun, and thus had their vitality 

 preserved. While trying to secure photographs of this breeding ground a few 

 of the old birds flew away, and it was surprising to see how quickly the newly- 

 hatched young succunibed to the heat when the parents left them exposed to the 

 rays of the sun. The nests were spaced at intervals of 4 or 5 feet, so that 

 the old birds were safely out of reach of one another. Although so gregarious 

 In their breeding habits, they appeared to have but little regard for one another. 

 It was amusing to see the savage way in which the nest owners assisted in- 

 truders of their own kind out of their territory. While we were walking among 

 them some of the birds would often waddle of£ to one side, and in so doing 

 necessarily trespassed on their neighbors. The latter at once raised a hoarse 

 shrieking and set upon the outsiders with wicked thrusts of their beaks, which 

 continued until the victims took wing and escaped. 



We were also subjects of this proprietary rage, and had our legs nipped 

 every now and then, despite all efforts to walk circumspectly. Our progress 

 over the breeding ground was accompanied by a wave of horse nasal cries that 

 sometimes became almost deafening. Many of the birds were valiant upholders 

 of their rights and sturdily refused to leave their nests, which they defended 

 vigorously, all the time uttering loud cries of rage. 



Eggs. — The Brewster booby lays ordinarily two eggs, but some- 

 times only one. The eggs vary in shape from ovate to elliptical ovate. 

 In appearance they are indistinguishable from the eggs of other 

 boobies; the color, bluish white, is obscured by a chalky coating, 

 which is dirty white, rough and often much stained. 



The measurements of 45 eggs, in various collections, average 61 

 by 41.1 millimeters; the eggs showing the four extremes measure 66 

 by 42, 65 by 45, 53.6 by 40, and 59.7 by 37.5 millimeters. 



Plumages. — The young booby is hatched naked, but soon becomes 

 covered with pure white down. The series of young birds in col- 

 lections is too limited to throw much light on the sequence of 

 plumages to maturity, but apparently an immature plumage is worn 

 for at least a year; this plumage is described by Doctor Nelson (1899) 

 as follows : " Dorsal surface uniform dark brown slightly paler than 

 back of adult; entire lower surface still paler and more dingy brown. 

 P^eathers over much of body, especially about head, neck, and lower 

 parts, narrowly edged with grayish brown, giving a faint wavy 

 barring." A male bird in this plumage was taken on April 23, 

 which was evidently a bird of the previous year, and several others 



