as were year-of-banding mallard and black duck recoveries, because most of the blue-wings 
were banded before the hunting season opened. 
LIFE TABLES AND TERMINOLOGY.--In the life tables presented here, mortality 
figures and survival figures were derived from figures representing the number of bands re- 
covered and the number of ducks banded in each of the various year-classes. Returns are com- 
plete for the first three year-classes; so the percentage of return is based on the total number 
of ducks banded, tables 1-7. For the fourth year-class (3-4), returns are lacking for 1 year 
(banding-class); so only the number of birds banded prior to that year are considered. Each 
succeeding year-class has returns for 1 year less; the 7-8 year-class has returns for only 1 
year. 
In the mortality* series, the percentage of the total number of bands recovered is 
given for each year-class, tables 1-7. The figure for any one year-class represents a per- 
centage of the total number of recoveries. 
The cumulative per cent of bands recovered, as presented in tables 1-7, is found for 
any one year-class by adding the mortality series figure for that year-class to the, mortality 
series figures for all previous year-classes. Figures in the survival series, the reverse of 
the mortality series, are obtained for any one year-class by subtracting from 100 the number 
representing the cumulative per cent of bands recovered for that year-class. The mortality 
rate, which measures the percentage of those birds alive at the start of a year that die in that 
year, is found for any year-class by dividing the mortality series figure for that year-class by 
the survival series figure for the previous year-class; for year-class O-1, the survival ser- 
ies figure for the previous year-class is 100 per cent. 
POPULATION LOSSES.--Mortality and survival figures of a population of ducks of 
known age are given in table 1. Banded as juveniles, the mallard drakes making up this popu- 
lation probably ranged in age from 3 to 7 months at time of banding at Lake Chautauqua. 
Data in table 1 indicate that in this population of mallards banded as juveniles, and 
therefore of known age throughout their history, for every 100 alive on October 1 of the year 
of banding 55 (54.9 percent) died before the next October 1. In the second year following band- 
ing, 20 additional ducks died; in the third year 11; in the fourth year 6. By the end of the sixth 
year, only 2 (1.9 per cent) were still alive. 
Mortality and survival figures for a population of mallard drakes banded as adults 
are given intable 2. The ages of the individuals were unknown except that all were at leasta 
few months more than 1 year of age at the time of banding. Data in the table indicate that for 
every 100 of these mallard drakes alive on October 1 of the year of banding 36 died before 
October 1 of the following year; 25 died the second year, 15 the third year, and 11 (10.5 per 
‘cent) the fourth year. By the end of the sixth year less than 3 (2.5 per cent) were still alive. 
The principal difference in the mortality rates of the two groups of ducks, one band- 
ed as juveniles and the other banded as adults, was in the greater year~of-banding losses in 
* The term mortality as used in this paper includes death caused by hunters and by natural 
forces; it is applied only to ducks that have reached flying stage. 
