32 



SEX AND AGE DETERMINATION 



Bursa of/r 

 Fabrlcius 



Anus 



- -Intestine 



(2) AGE DETERMINATION BY THE "BURSA OF FABRICIUS" 



Immature birds of the Ducks, Geese, and Swans can be distinguished 

 from adults by the bursa character. They cannot, however, be sexed 

 by this means as the bursa is alike in the juveniles of both sexes. 



The bursa is a sac-like organ (fig. 27) which empties into the dorsal 

 (or top) wall of the cloaca; it lies on the upper side of the large intes- 

 tine between the intestine and the spine. The opening of the bursa may 

 be seen caudal (behind or tail-ward) to the opening of the large intes- 

 tine, though the bursa itself is visible only on dissection. 



The bursa is present only in immature birds; it is always absent in 

 adults. It attains its highest development when the young bird is from 

 two to four months old. It then gradually becomes smaller until, when 



the young bird attains maturity, it disappears 

 entirely. 



In young birds the bursa is always pres- 

 ent up to the end of December; some indi- 

 viduals of all species retain the bursa as late 

 as April or May. In most species of ducks 

 the bursa disappears before the young bird is 

 one year old. (This group includes all of the 

 River and Pond Ducks and the Canvas-back, 

 Redhead, Ring-necked Duck, Scaups, and 

 Ruddy Duck.) 



After the end of December, as the bursa 

 may have disappeared, this character cannot 

 be relied upon to distinguish immature birds from adults. 



In Swans and Geese (and probably in those ducks that do not breed 

 in their first year, such as the Golden-eyes, Buffle-head, Old-squaw, Har- 

 lequin Ducks, Scoters, and Eiders) the burso does not disappear in some 

 individuals until they are more than a year old. 



The bursa was first described by Fabricius in 1621. Its function is 

 not fully understood. 

 METHOD OF EXAMINATION OF THE BURSA 



It is not necessary to dissect the specimen to examine the bursa. The 

 opening of the bursa of the juvenile bird is clearly seen upon examina- 

 tion of the cloaca, as described under Cloacal Method which follows. See 

 fig. 29. 



(3) AGE DETERMINATION BY STRIAE OF BILL 



Young ducks, geese, and probably swans, show striae (fine, narrow 

 stripes or streaks) on the tip of the nails of the 

 upper and lower mandibles (fig. 28). These 

 striae are generally absent in adults. If not 

 clearly visible with the naked eye, they can read- 

 ily be seen with a low-powered glass. 



Because these striae are often indistinct in 

 juveniles, and are sometimes retained in adults, 

 this is not entirely reliable as an age criterion. 



FIG. 27 



FIG. 28 



