LIFE HISTORIES OF NORTH AMERICAN PETRELS AND PELICANS. 185 



the region of the head and rump." The distinguishing features of 

 this plumage are well illustrated in the photograph reproduced in 

 the accompanying plate. Just how long this plumage is worn does 

 not seem to be known, but probably the adult plumage is acquired 

 before the end of the first year. Of the molts and plumages of the 

 adult I have been unable to learn anything. 



Food. — Regarding the food and feeding habits of the yellow-billed 

 tropic bird, Doctor Gross (1912) writes: 



The food of the tropic-bird consists chiefly of marine animals, which In the 

 majority of cases are secured by diving. The birds go on long foraging flights, 

 wandering, according to some observers, as far as 50 miles from land. On our 

 return trip to New York in 1910 a lone individual was seen which was estimated 

 to be 150 miles distant from Bermuda, and on June 25, 1911, I saw two of these 

 birds which were 200 miles from land. These are probably extreme cases, but 

 they serve to illustrate the unusually long excursions which the tropic-birds 

 may make in their search for prey. 



The food contained in the gullets and stomachs of 5 adult specimeus was 

 made up, for the greater part, of squids and flshes, especially small minnows. 

 In one of the stomachs there were a few fragments of a crab and a sea urchin, 

 as well as particles of material which could not be identified. Two of the five 

 kinds of fishes found belonged to a species of flying fish {Exocoetus furcatus and 

 Exonuutes exiliens) which are common in the waters of Bermuda. It would 

 be interesting to know whether or not these flying fish are captured while they 

 are sailing above the surface of the water. 



The adult birds are most active during the eai-ly morning hours; it is only 

 occasionally that they can be seen feeding during the middle of the day, the 

 heat at that time being, perhaps, great enough to account for the diminution in 

 their numbers. 



The numbers remained practically constant until about 8.30 a. m., when there 

 was a uniform but rapid decrease, and by 11.00 a. m. there was only an occasional 

 tropic-bird to be seen flying about. The birds were again active during the few 

 hours before sunset, but the numbers at this time never equaled those of the 

 morning hours. 



The diving of the tropic-bird is remarkable in that the plunge is usually made 

 from a height of 50 feet or more above the surface of the water. The bird, after 

 sighting its prey, poises a second or two in midair by rapidly vibrating the wings, 

 meanwhile maintaining a gaze on its victim. It then turns quickly at right 

 angles and, with wings floldfd, darts through the air with tlie swiftness and 

 precision of an arrow. Frequently this downward plunge takes the form of a 

 spiral descent. It is uncertain whether this spiral course is the result of a 

 voluntary act or not. 



Behavio?'. — The flight of the tropic-bird has been likened to that 

 of a large tern or a pigeon ; it is entirely unlike any of the other 

 Sfega?iopodes in all of its movements and seems to belong in a class 

 by itself; its flight is swift and graceful, accomplished by rapid wing 

 strokes. It is decidedly an aerial species and its feet have become 

 Aveak and abortive by disuse. Doctor Gross (1912) says of it: 



The birds nevet- walk upright, but the body is shoved along in a cumbersome 

 manner by their diminutive legs. The wings are often brought into service 



