PART III. IMPLICATIONS OF MORTALITY DATA, WITH SPEC 
| a , IAL REFERENCE TO 
Chapter XII.--Indices of Mortality, Hunting Pressure, and 
; Populations 
Use. of Seasonal Recovery Rates in the Past 
The Lincoln population index.—-More familiarly known as the 
Lincoln Index, this represents the first attempt to use seasonal 
recovery rates in a statistical ratio. Lincoln (1930) suggested that 
if we can obtain a fairly accurate statement of the number of water- 
fowl killed in any one season in North America, then 
.. , ' the no. of waterfowl banded e the no. of waterfowl in N. A. 
the m. recovered In thar Ist hnting seasm the no. killed by hunters 
Lincoln observed that the first-season recovery rates for waterfowl 
in the aggregate appeared to average about 12 per cent. If the total 
kill-by hunters was, say, 5,000,000 waterfowl, the fall population on 
the continent would be about 42,000,000. 
The difficulties attending the application of this index 
have been many. One serious obstacle has been the continued lack of 
reliable data on the total number of waterfowl taken by hunters. 
Another. has been the uncertainty as to the percentage of recovered 
bands: that never are reported to the Federal Government. Estimates 
have been presented by Leopold (1933: 156) that this is (or has been) 
SO per cent in Connecticut, 60 per cent in Arkansas, and 80 per cent 
in the Carolinas. McIlhenny (1934) has estimated that 50 per cent 
or less of recovered duck bands are unreported. More recently, 
Bellrose (1945) has concluded that this percentage has been only 
25 per cent in Illinois in recent years. This statistic was ottai ned 
from 509 post-card replies to a questionnaire sent to 1000 randcmy 
selected hunters. It may or may not prove to be accurate. If, among 
50.9 per cent of Illinois hunters who respond to é questionnaire con- 
taining a card for reply, 75 per cent have troubled themselves to 
report a band, van we be sure that the other 49.1 per cent who do 
not return a card have a similar degree of cooperativeness in report- 
“ing bands? Their failure to reply to the questionnaire casts some 
doubt on their cooperativeness. Bellrose's interesting study does 
permit us to say that the percentage of reported bands in Illinois 
is somewhere between 37.5 and 75 per cent. 
Recent attempts to get fairly accurate estimates of the 
hunting kill and detect the percentage of umreported bands hold 
some promise that the Lincoln index may yet be used as a check on 
waterfowl- numbers. As Lincoln (1930) says: "The figures could only 
be considered as approximations, but they at least have the merit 
of being based on factors that appear to have a definite relationship." 
If the index is ever used, the seasonal recovery rate should not, I 
feel, be a mean value covering many years of banding. A glance at 
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