Table 51.-<~A Preliminary Life Table for Great Horned Owls 
Based on nestlings banded from 1926 to 1941 inclusive, each year start- 
ing September 1. The number of banded birds available was ascertained 
by taking the recovery cards and checking them against the banders! 
original reports. The number banded by persons who got no recoveries 
was not determined. Its inclusion in this table would lower the 
values in columns 1', and d',, but would not seriously alter the 
mortality rates obtained here. The mortality series in this table 
represents the number reported dead per 1000 banded birds available. 
From it, the survival series is derived after the method of Lack. 
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; : q. 
Age No. Be Banded Mortality Survival Mortality Rate 


Interval or Found Birds Series Series (per cent 
in Years Dead _ Available 1000 [a,+(2)] per year) 
0-1 33 4,78 69.0 135.9 51 
1-2 9 78 18.8 66.9 
3~), 3 478 6.3 31.4 
y~S 1 4,78 2el 25.1 
6-7 ‘@] 337 - 20.5 2 
7-8 1 222 4.5 20.5 
8-9 0 178 - 16.0 
9=10 1 162 6.2 16.0 
10—11 0 128 - 9.8 
11-12 0 112 - 9.8 
Total and Mean 135.8 432.8 31 
sample. A second criticism arises from the fact that not all banded 
birds available for study were actually counted by me in the Fish and 
Wildlife Service files. (Time did not pe.mit me to determine the num 
ber of horned owls banded by persons who obtained no recoveries whatso- 
ever.) To test this criticism, I set up a small table of 20 birds 
banded prior to 1933 and later shot or reported as found dead. Using 
Lack's method, these 20 yielded a mortality rate of 50 per cent for the 
first year of life and a man rate of 26 per cent per year for adults. 
This result at least does not discredit the method used in table 51; 
it also carries the implication that the sampling errors in table 51 
may be less than originally suspected. 
In an effort to obtain further clues to at least the adult 
mortality rate for this species, 38 recoveries of horned owls banded 
as adults were examined. Nineteen of these were recovered within one 
month after banding, and most of these 19 were within one week. It seems 
obvious that the original capture of these adults either doomed many of 
116 
