SEX AND AGE DETERMINATION 



31 



SEX AND AGE DETERMINATION 



NINE METHODS 



(1) AGE DETERMINATION BY THE TAIL-FEATHER METHOD 



In the autumn it is often possible, by this method, to decide whether 

 a specimen of the Ducks, Geese, and Swans is a juvenile of the year or 

 an adult bird. Proceed as follows: 



(a) If the tip of the tail-feather is normally rounded or pointed 

 the specimen is an adult bird (fig. 26 c). 



(b) If the tip of the tail-feather is V-notched or square-ended the 

 specimen is a juvenile (fig. 26 b). 



The reason for this difference in the tail-feathers of the adult and 

 immature bird is that the down which precedes the juvenile tail-feathers 

 is attached to the ends of their shafts (fig. 26 a), and when the shaft of 

 the down breaks off, that of the tail-feather shows a resulting blunt tip 

 (fig. 26 b). In succeeding moults, the tail-feathers are replaced with 

 others of their own kind, and the tips of the 

 adult tail-feathers are, therefore, normal (fig. 

 26 c). 



The use of the tail-feather character as a 

 means of determining age is limited to the 

 time before the juvenile tail has been moulted 

 and replaced by the tail of the first winter 

 plumage. This period varies greatly even 

 with individuals of the same species; early- 

 hatched birds will complete the moult of the 

 tail sooner than late-hatched birds. Until the 

 time when the young birds lose the juvenile 

 tail, all juveniles may be distinguished from 

 all adults by the tail character. 



Examine the tail-feathers carefully. If all, some, or even one of 

 the tail-feathers are notched the bird is a juvenile. If none is notched 

 the bird may still be a juvenile which has completed the tail moult, or 

 it may be an adult. 



Early dates of completion of the tail moult: The exact date of the 

 earliest tail moult in the various species is not known. In the Pintail 

 and Wood Duck, all juveniles probably wear the juvenile tail until late 

 in August; all Mallards and Black Ducks until the first week in Septem- 

 ber. In all of the other species of the River and Pond Ducks, and in all 

 Canvas-backs, Redheads, Ringnecks, and Greater and Lesser Scaups the 

 juvenile tail is always worn until mid-September. In all of the other 

 Diving Ducks the first of October is probably the earliest date for the 

 completion of the tail moult. In geese and swans the juvenile tail is 

 not replaced by adult feathers until late autumn or early winter. 



The foregoing are the earliest dates for the moult of the juvenile 

 tail; many individuals of all species, however, do not complete the tail 

 moult until late in the autumn and in many cases some juvenile tail- 

 feathers persist well into the winter. 



FIG. 26 



