than the mean adult mortality rate. There is, however, some reason to 
believe that-~if such existed in this species--it would not necessarily 
be detectable in the mortality data analyzed here. The sample of birds 
shot, when added to the birds found dead, appears to be too small to 
masters what is happening to the population during the autumnal 
perloGe 
‘Table 53.--Calculated Mortality Rates for Blue Jays 
# means banded as juveniles; age intervals start as of September 1. 
# means unaged at time of banding; age intervals start as of January 1. 
Source of “Size ef Cohorts Calculated Mort. Rate Analytical 
Recovery Sample Used Ist-Year Adult (mean) Method 
117% 1926-36 38 39 ‘Lack (193a) 
Found Dead 153% 1926-1 3h 37 Per 1000 banded 
LST# 1926-36 -- 45 Lack (19)3a) 
150% 1926~36 yl 42 Lack (19)3a) 
Found Dead 211% 1926—)1 ho 0 Per 1000 banded 
or Shot 636# 1926~36 —— 45 Lack (1943a) 

Some comment is needed on the pronounced tendency of these 
banding data to yield a higher mortality rate for adults in contrast 
to that calculated for first-year birds. This is either a band-loss 
effect or something actually occurring in nature. Without productivity 
data, it is difficult to identify the actual reason at this time. Part 
of the circumstantial evidence for a constant adult mortality rate in 
wild birds lies in the comparison of longevity in captivity. There is 
much evidence that, in the’ wild, birds attain only a fraction of the 
life span they achieve in captivity (Gurney 1899, Flower 1925 and 1931, 
Farner 1945, Marshall 197). This situation strongly implies that 
senility with its presumed increase in vulnerability to predation and 
‘other environmental hazards is seldom attained by birds under natural 
conditions. 
For the record, I should add that near Ann Arbor, Mich., my 
wife and I for several weeks observed a blue jay with a thin, much- 
worn band that was partly open and about to come off the bird's leg. 
We feel certain that this individual did lose its band before my 
wife was finally able to trap it. 
Details of the uncorrected mortality data for blue jays unaged 
at the time of banding are given in table 5. If band loss does occur 
in this species, it is probable that the first four age intervals are 
the most accurate ones. Extension of a line through these points 
(figure 12) suggests that about 22 more birds might have been recovered. 
These would represent a band loss of about 3.4) per cent. Added to a 
life table they would drop the mean adult mortality rate to l2 per cent 
per year. 
121 
