1920 J Dwight, Plumages of Gulls. Zbo 



Another source of confusion in the study of Gulls is due to the 

 fact that different areas of plumage in the same bird advance to- 

 ward maturity at different paces, although no changes in plumage 

 save fading occur except at periods of moult. The flight- 

 feathers of the wings and the quill-feathers of the tail are moulted 

 but once in the year while the plumzge of the body is moulted 

 twice, so that evidences of immaturity are lost sooner in the body 

 plumage. Nor do discrepancies of development stop here for we 

 may find well developed wings and tail combined with a backward 

 body plumage or vice-versa. But in spite of complications it is 

 possible to group together certain characters so that we have defi- 

 nite plumages representing the average advance made at each 

 period of moult. It may be well to first take up separately each 

 of the several characters by which we may judge the age of a given 

 specimen. 



1. Shape of primaries and rectrices. Perhaps the most import- 

 ant of the characters is the structural difference in the shape of the 

 primaries and tail-feathers of birds in their first year as compared 

 with those of a second or later year. My attention was directed 

 to this by Mr. H. Ira Hartshorn who in making drawings to scale 

 for me found discrepancies to exist. An examination of specimens 

 of Gulls of the world shows that throughout the first year, and un- 

 til the first postnuptial or annual moult, the primaries as a rule 

 are more pointed and the rectrices more rounded than in later 

 years. The new second year primaries acquired at this moult, 

 which removes the juvenal wings and tail, have more rounded, 

 broader tips than in the first year, being practically the shape of 

 fully adult feathers. There is some variation, but as a rule in 

 first year birds, the extreme tip appears to be pinched to a point, 

 the outer or distal feather usually showing this pecularity more 

 markedly than the others (see Plate X, fig. l,and Plate XI, fig. 1). 



A similar difference in shape prevails in the tail-feathers of Gulls, 

 first-year or juvenal rectrices being rounded (see Plate X, fig 2, 

 and Plate XI, fig. 2) and replaced at the first postnuptial moult 

 by feathers of the second year which are more or less squared at 

 the tip (see Plate XII, fig. 2). The outer rectrix is perhaps the 

 most diagnostic and as the wings and tail are moulted only once a 

 year the value of these characters is great, for many birds after 



