represent a ratio of about 1.6 young (315 + 200) per adult. This 
ratio is subject to two possible refinements. A correction for 
failure of some females to mate might be made. I regard this as 
probably unnecessary. A second correction would be made to allow 
for mortality in the adults that were censused at the start of the 
season. Bearing in mind an annual adult mortality rate of the 
order of 55 per cent for this species, per cent per month is not 
too absurd an estimate. For a 3=month period, this could be 
roughly construed to mean a 12 per cent decrease from 200 adults 
censused on June l--a drop of 2h birds, leaving 176 alive on Septen- 
ber 1. The ratio of 315 young to these 176 is 1.8 to 1. This may 
be regarded as an upper limit that could be considered in popula- 
tion analyses of this species. 
Vulnerability of the young.==-In discussing the relative 
vulnerabillties of adults and young to the gun, we can in the case 
of the redhead usefully assume that some of the results may well 
be due to differences in migratory behavior. Vulnerability in 
this species changes chronologically as well as geographically. 
For 372 Utah redheads (table 31) shot in September and October, 
6 juveniles were bag-ed for every adult; for 122 shot from Novem- 
ber to Jamary inclusive, this ratio was 2.5 to 1, Taken geo- 
graphically, these ratios are 33 to 1 for 171 birds shot in Utah, 
3.4 to 1 for 166 birds shot in southern Canada and northern United 
States, and 2.6 to 1 for 83 shot in Mexico and the southern states. 
For Canadian-banded redheads (table 32), 3.2 young per adult were 
reported among 2 shot in Canada, 1.1 per adult among 6 shot in 
the northern tier of states, and 0.9 per adult among 72 shot farther 
south. 
If the age ratio in the population is about 1.8 juveniles 
per adult cn September 1 (as a purely preliminary estimate) and the 
age ratio is h.2 to 1 in hunters' bags (table 33, part A), it 
follows that juveniles are more than two times as vulnerable to 
gunning as adults are throughout the entire hunting season (that 
is, 2 = 1.8 = 2e3)6 
Annual mortality rates.--A rough approximation of the 
age ratio on February L can, 1 think, be implied from the adult 
mortality rate in this species. With about 55 per cent of the 
adults dying each year, stable populations will need to consist 
of 55 young for each 5 adults at the start of the breeding season 
(or at the end of the hunting season when adult and juvenile mor- 
tality rates become equal). We can then readily calculate a true 
annual mortality rate for young birds from these statistics--— 
alive at start; 180 young ~- 100 adults (1.8 y/ad.) 
alive end of year: 55 young - 45 adults (1.2 y/ad.) 
number dying 125 young - 55 adults (2.3 ¥/ad.) 
78 
