Table 37.—-Monthly Variation in Recoveries Reported for Caspian 
Terns Birds Banded from 1922 to 19h1 
(Frequency by months, August to July) 


flow Obtained Tr Vi Total 
In first Year 
Shot - 3 25 1 2- - 1121 - 16 
Found dead 5 9 10 6 1 5 3 2 0 3 4 1 9 
Captured hi 8 - 2 3 3 = - 1 -1 1 23 
—wral 5 20 1213 5S 0 3 2@ © GYo6o io oO 
As Older Birds 
Shot 2 - - 8 3 hl-s- -i1-' 4 23 
Found dead 7 9hil1 3 Lh h 2 3 hil 3 52 
Captured 2 5 21 2 2=- 2 1 2 2 - 21 
Stal ll Wm i331 86 10 5 4 Ls?) 7 96 

reported found dead, 30 were reported shot, and 5 taken by scientific 
collectors for 5 different museums in the United States and Canada. 
Some of the dead birds in table 37 were excluded here because they 
pana oe in 1922 to 1925 when the durability of bands was subject 
to doubt. 
This small sample yields mortality rates of hl per cent 
per year for the first year of life, 26 per cent for the second year, 
and a mean of 18 per cent per year for age intervals past this point. 
Mortality rates calculated for age intervals from 2-3 to 8-9 show no 
wide fluctuations, the actual rates varying from 11 to 17 per cent 
a seed and the mean for these 7 age intervals being 15 per cent 
This table involves small numbers, some of which exhibit 
sampling errors that are further distorted by the statistical method 
employed here to set up a mortality series. An examination of the 
survival curve (figure 9) on semilogarithmic paper further emphasizes 
the inadequacy of the data. The survival curve begins to drop after 
age interval 8-9, suggesting band loss. Had the curve continued 
with the same slope, the population would not have been reduced to 
one per cent until age 27-28. Failure of the birds in table 38 to 
attain such an age may be also due in part to the extremely low 
recovery rate, as well as the absence of very large banding opera- 
tions in the early 1920's. 
Age ratios and productivity 
The age ratio of the population shown in column 1‘, of table 
38 cannot be critically evaluated without some knowledge of Zhe age 
at which most caspian terns begin to breed. If all the adults in 
this table breed at age 3, each pair would have to raise 1.1 young 
to August 1 to keep the population stable. This can be compared to 
1.5 young per successful nest noticed by Miller in 37 nests on the 
89 
