THE 



NA/ILSON BULLETIN 



NO. 97 



A QUARTERLY JOURNAL OF ORNITHOLOGY 



VOL. XXVIII DECEMBER, 1916 NO. 4 



OLD SERIES VOL. XXVIII. NEW SERIES VOL. XXIII. 



THE MATING AND NESTING HABITS OF 

 FREGATA AOUILA. 



BY PROFESSOR HOMER R. DILL, 

 STATE UNIVERSITY OF IOWA. 



Among the many interesting birds to be found on Laysan 

 j^ Island, perhaps/ one of the first to attract the attention of the 

 visitor is the man-o'-war, Fregata aquila (Linn.). Float- 

 ing gracefully a few feet over head it follows a new comer 

 about with curious interest. One cannot fail to be impressed 

 with the beauty and grace of these creatures. The male is 

 especially distinctive with its jet-black body, iridescent scap- 

 ulars, long forked tail that opens and closes at intervals like 

 a pair of shears, and its unique gula-pouch, that, during the 

 mating season, is inflated into a large sack-like afifair, bright 

 red in color, and for all the world like a toy balloon. 



Naturalists have speculated long as to the use of this gula- 

 pouch of the man-o'-war bird. During a several weeks' resi- 

 dence on Laysan, which fortunately fell at the season when 

 the mating and nesting of these birds was at its height, a 

 careful scrutiny of their habits convinced me, at least, that 

 while it served primarily for the attraction of a mate, the 

 gula-pouch may be used also as an aggressive feature with 

 which to frighten an enemy. 



Man-o'-war birds were found nesting in large colonies, 

 many acres in extent, building their nests on the tops of low 

 bushes. In some places their nests were so close together 



