Table 41.—-Disappearance of Common Terns in a Retrapping Program 
The implied age structure of the Cape Cod nesting population found 
by Austin (1942) is given in columns L, and L! Many birds do 
not nest until age or 5 and so are cnrucandad? in the trapping 
program at the nesting colonies. Column L'', attempts to weigh 
the returns in column L, according to their availability as shown 
in column B. No correction was attempted to eliminate trapping 
inefficiency and thus permit calculation of mortality rates. 
These birds were banded as nestlings. L'', = 10,000 (L, + 8B). 

7 > 
x a e 
Age No. Re~ Per Cent No. Origin= No. Fe- No. Dis=- Disapyear- 
When trapped of ally Banded trapped appearing ance Rate 

hepatic on Total (1,2, ie: per 10,000 between (per cent 
(in years) Nests Retrapped yrs.before) Banded Ages per year) 
1 Ly 1.7 30,580 1.4 
2 99 3.7 27,94 35.4 
3 417 15.7 29,620 10.8 
h 688 25.9 355373 194.5 289 
S 566 21.3 34,170 165.6 68.9 2 
6 334 12.6 34, 548 96.7 21.8 23 
7 226 8.5 30,180 The9 346 46 | 
8 83 361 20,571 hO.3 9.6 2h e 
9 62 204 20,212 30.7 5k 18 
10 hs Br Lg 155 2503 562 21 
11 30 lel 1; ,906 20.1 5.3 26 
12 2h 0.9 16.174 1,.8 7.9 
13 12 0.5 15,461 7.8 -0.9 
ly 11 O4 12 , 330 8.9 1.3 
15 6 0.2 7,925 7.6 2el 
16 2 0.08 3,962 5.0 5.0 
17 0 0 1,392 — 0 
18 0 0 392 @] 
19 0 0 oh 0 
Totals and means (age 5 to 16) 502.7 167.1 33 
Totals and means (age 6 to 9) 22.6 71.4 29 
Totals and means (age 10 to 16) 94.5 25.0 26 
disappearance of the last bird depends on the size of the statistical 
sample being studied. For 1000 common terns subject to the 32 per 
cent annual disappearance rate implied in figure 11 and under con- 
tinuous annual observation from age onward, the last individual 
should be recorded at age 25; for 500 adults, this would mean age 
19 or 20; for 100 adults, this would mean age 18. If the actual 
mortality rate is 17 per cent as Austin (199) says, the last 
individual would live very much longer. The recent report of a 
comnon tern at least 20 years old (Austin 194:7b) surely is no sur- 
prise. 
98 
