It seems certain that in this species we have encountered 
a rather low adult mortality rate. The monthly distribution of the 
banding recoveries is well spread out throughout the year. This 
implies that the first-year mortality rate calculated in this study 
is not biased by a heavy preponderance of shooting reports in the 
fall of the year, although the size of the sample does not permit 
one to regard the result with confidence. 
Both the horned owl and the blue jay (which follows in 
the next chapter) present difficult problems to a field invest? -ator 
interested in obtaining statistically significant data on average 
productivity. Nesting information for both species might well be 
gathered by an organized inquiry using a questionnaire. 
Summary 
3 Three separate analyses of horned owl banding data indicate 
that the mean adult mortality rate is of the order of 20-25 per cent. 
The samples examined were all quite small, and the estimate obtained 
here must be regarded as an approximation. A first-year mortality 
rate of Sl per cent, obtained for 58 birds banded as nestlings, is 
obviously subject to sampling error and not easy to verify at this 
time. 
Mortality reports of &6 banded great horned owls were 
rather well distributed throughout the year. The oldest bird thus 
far recovered had reached age interval 12-13. 
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