Table 1/.-~Approximate Age Ratios in Double-crested Cormorants 
These birds were banded as young through 191; the ratios cover 
all usable reports received at Patuxent Research Refuge to August 
31, 1946. "Juvenile" represents birds in their first year of 
life (August 1 to July 31). “Adult* in this table means all 
other birds past this first sage interval. 

(I) (2) + 3+ Reported 
How Where Number Reported ~ dJuv./ Aug. 1 - Nov. 30 
Obtained Banded Juv. "Adult" Total Juv. Ad. JUV. Ad. 
% % 
Shot Inland 348 86 434 80 4.1 89 71 
n Coast 128 26 1Sh 83 5.0 77 am 
" Total h76 112 ~ °&# 588 81 4.2 86 6h 
Fd. dea nian 0 . = iv 
" ad Coast 93 21 11, 82 Lol 70 - 
" n Total 161 61 222 73 26 71 57 
Captured 
by fishermen 80 38 118 68 21 68 - 
by misc. persons 85 25 110 77 3. 85 - 
% Maximal values that will decrease when additional reports of the 
banded adults become evailable 
No double-crested cormorant population with an age struc- 
ture similar to that of these marine-banded birds could possibly 
maintain itself. We must conclude that the data in table 19 are 
biased. A.close inspection of the two mortality curves in figure 8 
-reveals a gradually widening gap between the two. I infer that the 
increase in this gap principally represents band loss due to salte 
water conditions, The small size of the samples possibly obscures 
the time when this loss begins. It would appear to be well under- 
way during age h-5 and (in this sample) complete by age 7-8. 
As a check on the effect of band loss in life-table 
statistics, IT recalculated table 18 using only the first 7 years 
of mortality data. This procedure yielded a first-year mortality 
rate of 79 per cent (cf. 80 per cent for the marine-banded birds) 
and a mean mortality rate of 71 per cent for all ages (cf. 66 ver 
cent for marine birds). This agreement would appear to represent 
a type of experimental evidence that band loss is occurring among 
marine—banded cormorant populations. Band loss may occur among 
the fresh-water birds, too, but I was unable to appraise it at 
the time of this study. 
The two mortality curves illustrated in figure 8 display 
minor peaks for age 5-6. There seems to be no possibility that these 
were caused by climatic conditions. One wonders if these are possibly 
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