The peak of occurrence for 95 of these (recovered after December 31 
of the year in which they were banded) was found to coincide closely 
with that of the juvenile-banded birds, Whatever the actual causes 
of mortality may be, their peak occurrence in the breeding season 
seems important. 
If the age ratio of the birds dying each year between 
September 1 and August 31 in Blue jay populations is 0.54 young to 
1 adult (as in the birds found dead in table 54, samples of h9 would 
show an even age ratio about once in 20 times. It seems best, there- 
fore, to regard the 49 birds shot (table 52) as biased in favor of 
juveniles and to use them only with caution in an abridged life 
table. 
Table 52.—-Monthly Variation in Recoveries of Banded 
Blue Jays 
Based on birds banded as young during the months of May, June, July, 
and August, from 1923 to 1941 inclusive. Some of the recovery dates 
may include slight clerical errors but the seasonal trends should be 
accurate within the limits of the size of each sample. Age ratios 
implied in this table are subject to additional reports of adult 
birds being recovered after 196. | 
Frequency of Reports ontns (September to Augus 
Age Reported IX X Xi XIll I If Til IV V Vi Vil Vill Total 
Found dead 
First year 8 5 3 4 & 2 3 210 7 3.0C BS oh 
Adult 8 5 8 210 6 61312 15 Ww 9 7 ~~ 101 
Total 1610 11 #6 Wy 8 9 13 25 21 22 =#«10 155 
Shot 
First year 3 6 Oo & 3 oO 1 0 2 0 3 2 2k 
Adult h 5 2 lL 2 1 0O Qa QO 8 2 0 25 
Total 7 12 2 5 § 1 1 2 8 5 4 4,9 
Abridged Life Tables 
In order to avoid any possibility of substandard bands in- 
fluencing the mortality statistics, banding operations from 1923 to 1925 
inclusive were not used in constructing life tables. Six such tables 
were set up, and the results are summarized in table 53. Here for the 
first time we encounter a first-year mortality rate that does not seem 
to be higher than the man adult mortality rate. Lack (19h6b) has 
shown that the higher mortality rates for young songbirds drop to those 
of the adult birds by January 1. The recovery reports of blue jays 
found dead are more frequent in the spring than in the autumn (table 52). 
We apparently are faced here with a situation that was theoretically 
explored in Chapter III, table 13. There is no proof that the first- 
year mortality rate (September l—~August 31) for blue jays is higher 
120 
