Redhead 
Literature on productivity and survival 
SS EE «CREE | eEneeeetnemcinny 
Aythya americana is one of the few ducks on which a quan - 
tive nesting seaay has been published. During 1938-0 in Towa’ ABs 
Low (1945) found that clutches averaged 9.8 eggs, that 45 per cent of 
these eggs produced young, and that approximately 70 per cent of the 
young reached the start of their first fall migration. Signs of fall 
migration were evident as early as August 20. 
Banding work in North America 
_ The principal banding work on redheads has been carried out 
in Utah's Bear River marshes by Fish and Wildlife Service personnel: 
A. Ve Hull, F. C. Lincoln, Alexander Wetmore, and G. E. Musbach, 
whose 460 recoveries of juvenile-banded birds made up the bulk of 
life-table data available for this study. Wetmore's pioneer work in 
1915 and 1916 was not used in my compilations, because of the uncertain 
permanency of the bands. 
Characteristics of the sample studied 
The migratory distribution of juvenile Utah-banded birds 
has been mapped by Williams (194), who also demonstrated that most 
of the Bear River Redheads reported shot by hunters are actually killed 
in their first autum. This latter phenomenon is so striking that a 
monthly distribution of the hunters! reports is given in table 31 
where about 12 per cent of the dates consist of approximations made 
by banding clerks. Of the juvenile birds reported shot in their first 
autumn, 78 per cent were apparently killed in September and October. 
This is impressively higher than a value of 46 per cent that I 
similarly calculated for 457 juvenile mallards. A parallel segrega- 
tion of adults reported shot in the first 6 weeks of the season 
(361 per cent) may be contrasted to 33 per cent for a small sample 
of adult mallards. Since it would appear that these redheads were 
markedly more sensitive to hunting pressure than mallards, a compari- 
son of mortality curves of the two species becomes particularly 
interesting. 
Williams (194) has clearly shown that the Utah-raised red- 
heads winter principally in the Salton Sea area of southern California 
and on the lower coast of Texas. Lincoln's (1939) postulation of a 
migration route from Bear River to Chesapeake Bay unquestionably has 
some bias, but--as Robbins (1949) tas shown—~the annual magnitude of 
this pehnomenon is almost negligible. 
The dual wintering grounds of redheads raised in the prairie 
provinces are demonstrated in table 32. This particular unit of the 
redhead population was banded mostly by personnel of Ducks Unlimited 
(Canada) since 1939 and occupies a minor role in the life tables that 
follow. 
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