Vol. XXIXI 



1912 



] Gross, The Yelloiv-billed Tropic-bird. 55 



The numbers remained practically constant until about 8 : 30 a. m., 

 when there was a uniform, but rapid decrease, and by 1 1 : 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 equalled 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 mid-air by rapidly vibrating the wings, meanwhile main- 

 taining a gaze on its victim. It then turns quickly at right angles 

 and with wings folded darts through the air with the 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. 



Nests of the Tropic-bird were found in favorable places among 

 the cliffs at Ely's Harbor, Hungry Bay, Tucker's Town, Harring- 

 ton Sound, Castle Harbor, Spanish Point and on nine of the islands 

 of Great Sound. Verrill ^ estimated that 2000 pairs were breeding 

 in the islands in 1901. x4pparently the numbers have not changed 

 very much since that time. The majority of the nests found dur- 

 ing the latter part of June contained either eggs or else young in 

 well advanced stages of development. This fact, correlated with 

 the time of arrival of the birds and the period of nesting, indicates 

 that there are probably two nesting periods in a season. Bucken- 

 ham - states that several broods are reared during the year. There 

 are doubtless two, but certainly not more than two, broods in a. 

 season reared ))y these bu'ds while in the Bermudas. 



Particular localities, especially on the south shore of the main 

 island, seemed to be preferred by many of the birds. At Ely's 

 Harbor and Tucker's Town it was not unusual to find as many as 

 50-75 pairs nesting within a range of less than 100 yards. The 

 Tropic-birds are not, however, strictly gregarious, for isolated 

 nests about the islands of the sound were very common. The 

 so-called colonies probably exist because of the many choice nesting 



1 The Bermuda Islands, 1901-03, p. 680. 

 ^ Museum, 1894, pp. 1,5-16. 



