Table 36.—Age Intervals in Which Marsh Hawks were Reported Shot 
‘Based on birds banded as nestlings prior to 1937; a small and 
ab 
insignificant number remain to be reported past age 9=103 ea pane 7 
starts August 1. The letter x below means that full data for this 
age interval were not yet avallable when the table was compiled. 
(a) (T) (q 
Age Interval Number Number Alive Morteli i> Rate 

{in years Shot Start of Year r Year 
O-1 58 99 
1-2 13 1 - 
2—3 10 28 
eh 5 18 
h=5 3 13 
5m 3 10 
6=7 2 7 
7-8 2 5 
9 0 3 0 
9-10 2 3 ane 
10-11 x (1) 
11-12 x (1) 
12<13 x (1) 
13-14 x (1) 
We-15 x nt 
15-16 x 1) 
16-17 | (1) (1) 
Total 99 (+ ?) 23h h2¢ 
appear to be atypical of samples of 100 marsh hawks. Its elimination 
from consideration in the above age ratio would raise the number of 
juveniles in the population to 0.8 per adult on August 1. Although 
this is still subject to sampling aberrations, it can be used to obtain 
a working explanation of marsh hawk vital statistics as they are now 
discernible, 
The productivity of marsh hawks in North Dakota ran about 
322 young able to fly per successful nest (Hammond and Henry 199). 
Roughly 70 per cent of their nests fledged one or more young, 16 
successful and unsuccessful nests fledging an average of 2.2 young - 
per nest. Such a scale of productivity represents a mean of 1.1 
young for every breeding adult that started the nesting season. 
- Population dynamics 
How can an age ratio of the order of 0.8 (or 0.7) juveniles 
per adult on August 1 be explained in the face of a productivity of 
3.2 young in the fledging stage in successful nests? If the mortality 
rates in the life-table analyses here are even approximately correct, 
85 
