ON CERTAIN SECONDARY SEXUAL CHARACTERS IN THE 

 MALE RUDDY DUCK, ERISMATURA JAMAICENSIS 

 (GMELIN). 



By Alexander Wetmore, 



Of the Biological Survey, United States Department of Agriculture. 



Among recorded peculiarities of the ruddy duck (Erismatura 

 jamaiceTisis) the lack of an enlargement at the bronchial bifurcation 

 of the trachea in the male has been most noteworthy. The absence 

 of this hullu ossea, is the more striking as such an ampulla is developed 

 with comparatively few exceptions among all of the river and sea 

 ducks. MacGilhvray,* apparently the only ornithotomist to examine 

 and describe the trachea in the ruddy duck, first noted this pecuhar- 

 ity. Forbes found that a bulla ossea was lacking also in the male of 

 the Austrahan duck, Biziura lohata, and in his discussion of this fact 

 calls attention 2 to MacGiUivray's note on Erismatura. Later Bed- 

 dard^ noted that males of Oidemia nigra and Oidemia fusca also lack 

 this modification of the syrinx but did not give full enough credence 

 to MacGillivray's account to include Erismatura in the same category 

 unreservedly. In dissections of Erismatura jamaicensis made 

 recently I have verified MacGillivray's observations of eighty or more 

 years ago and have found in addition a remarkable secondary sexual 

 structure that has apparently never been described. 



Ornithologists who have skinned and prepared various species of 

 ducks are famiUar with the fact that in the ruddy duck the skin of 

 the neck is fuU and loose, sUpping easily over the occiput. In most 

 other species of ducks it is necessary to slit the integument of the neck 

 in skinning out the head. While examining a fresh specimen of the 

 male ruddy duck my attention was attracted to the broad develop- 

 ment of the paired dermal muscle (the deeper layer of the cucuUaris) 

 covering the ventral side of the skin of the neck. Further examina- 

 tion revealed a median broadening of the muscle stemo-trachealis 

 and finally a remarkable tracheal air-sac which is used when males 

 are displaying during mating. This tracheal air-sac has no con- 

 nection with the pulmonary air-sacs of the body. It opens as a 



1 Audubon, J. J., Ornithological Biography, vol. 4, 1838, p. 331. 



s Forbes, W. A., Collected Scientific Papers, 1885, p. 355. 



> Beddard, F. E., Structure and Classification of Birds, 1898, p. 464. 



PROCEEDINGS U. S. NATIONAL MUSEUM, VOL. 52-NO. 2191. 



