Vol. XI XT ^^^y,,sT-EV., An Undescribed Form of Black Duck. I 83 



1Q02 J 



Near the anchored steamer were many Terns {Sterna hirundo) , 

 but I could not tell whether or not they live on the cliff. 



The length of the cliff inhabited by the birds is about one mile. 

 By counting the birds on a section of the cliff, we estimated the 

 number of birds at not less than 60, 000. The photographs (PI. 

 VII) were taken under very unfavorable circumstances, owing to 

 foggy weather, but may help to give some idea of the abundance 

 of the birds. 



AN UNDESCRIBED FORM OF THE BLACK DUCK 

 {AJVAS OBSCURA). 



BY WILLIAM BREWSTER. 



It is a matter of common belief among our more intelligent and 

 observing wild-fowl gunners that two kinds of Black Ducks are found 

 in New England, and certain of the characters by which they are 

 thought to be separable have been mentioned, as well as briefly 

 discussed, by writers on ornithology or field sports. To one, a 

 comparatively small, dark race having a dusky or olivaceous bill 

 and brownish legs, all our local or breeding birds are supposed 

 to belong ; the other, a larger, lighter-colored form with clear yel- 

 low bill and bright red legs, is known to occur only during migra- 

 tion or in winter. I have often been struck by these and certain 

 other differences which will be mentioned later, and for the pur- 

 pose of testing their value and significance I have brought together, 

 with the kind assistance of several of my friends, a large series of 

 specimens most of which were obtained in New England in autumn, 

 winter or early spring. Among them are a dozen or more col- 

 lected in late August and early September at Lake Umbagog, 

 which almost certainly represent the form resident in summer 

 throughout New England although I have none from any locality 

 south of the Gulf of St. Lawrence which were taken at the height 

 of the breeding season. Some of my specimens were weighed 

 before being skinned and many of them are accompanied by notes 



