Table 19.—-An Abridged Life Table for Marine-banded Double- 
crested Cormorants 
Based on young birds banded in nesting colonies and 
shot and found dead. Each age inte pat starts as BE AteEn Ue 
possible bias in this table is explained in the text. In addition 
to marine-banded birds shown in table 15, this table includes 42 
birds banded in Califomia and Oregon. Calculations for the 3 
columns on the right are similar to those in table 18. Age inter- 
vals are in years; mortality rates are per cent per annum. 
Oy : a ©5526 9 
Age ass Banded Number Morta y 
Year Number to be Birds Recovered Series Survival Mortality 
Banded Studied Availabb (by age class) 1000 fd,+()] Series Rate 

1945 = 0-1 6235 239 38.3 47.8 80 
194, = 1-2 6235 22 3.5 9.5 
1943 = 2-3 6235 13 2.1 6.0 
19h2—=- 3-4 6235 8 1.3 3.9 
191 2320 eS 6235 6 1.9 |—62G 
19,0 82) 5-6 3915 h 1,0 1.6 
1939 633 6=7 3091 2 0.6 0.6 
1926-38 2458 7-8 21,58 0 0 0 
Total 6235 ~ - 294 47.8 72.0 66 
Totals and Means (years 1-2 to 6-7)- 9.5 24.2 39 
@ subsequent chapter on certain Laridae which exhibit a defemnent of 
sexual maturity until at least the third year of life. 
It should also be pointed out that, from the very start of 
each life table, marine cormorants are reported consistently less than 
fresh-water cormorants. I infer that this difference is principally ive 
to the relative inaccessibility of dead birds once they are shot or die 
on the seacoast. The difference in recovery rates for the two groups, 
brought out in table 16, may primarily be due to the relative ease with 
which carcasses are recovered under fresh-water conditions and secondarily 
(at least at first) to band loss under salt-water conditions. 
Juvenile mortality rates.-=-The potential bias in reports of 
juveniles shot may now be examined in table 18 by making a productivity 
analysis of the population implied by the survival series 1',. Simple 
calculations show that if all the adults begin breeding at age 2-3 and 
all raise 2.5 young per pair to August 1, they will raise about 87 per 
cent of the young necessary to keep the population stable. I therefore 
feel that the presence of shot birds creates a bias in this life table, 
although it does not invalidate the comparison with an adult marine 
population recovered in a similar manner. There appears to be much 
less likelihood of this bias importantly affecting the mortality rate 
53 
