Table 33.—-Abridged Life Tables of Redheads 
Based on hunters! reports of birds banded as young before Septem 
ber 1. The data on the left are based mostly on birds banded in 
Utah; the more recent data on the right include banding work in 
Canada. Mortality rates are per cent per annum. 


rr... | Mek = oe ae ae 
Dynamic Life Table Time-specific Life Table 
Birds Banded 1926 to 1935 Birds banded 1926 to 192 
Age Number Alive at Mortality “Number Calculated Mortality 
Interval Reported Start of Rate Reported Mortality Rate 
(in years) Shot Year Shot 
@) GQ) (a) a) @) @ 
0-1 410 71 87 537 1,87 91 
1-2 40 61 50 23 ; 
2-3 ys 21 27 15 49 
3-4 3 7 12 - 
h=5 i 4 
5=6 0 3 
6=7 0 3 Sh 
7=8 0 3 
8-9 1 3 
9-10 0 | 2 
10-11 0 2 
11-12 0 2 
12~13 2 2 
Adult Totals 
and Means 61 113 5h 77L/ 38 49 
T/ excluding age 3-]y 
season, and (2) a better approximation of the mean adult mortality 
rate than the one obtained in this study. The need for these data 
can be illustrated by setting forth the population dynamics of this 
species with the statistics and estimates currently available. 
Age ratio on September 1.—J. B. Low (1940) has used the 
ideal field technique to obtain an estimate of the age ratio in a 
redhead population at the start of migration. This involves a 
careful census of the breeding pairs on a series of study areas and 
close follow-up observations to determine the number of young that 
hatch, reach the flying stage, and subsequently leave the area. 
Low (190) concluded that on his study areas in Iowa in 1938 approxi- 
mately 380 young succeeded in entering the fall migration and that 
this number represented an average of 3.8 juveniles per breeding 
pair. The sex ratio obtained by Low (1941) for a 3-year period was 
1.42 males to 1 female among 3400 redheads. This wuld imply that 
for each 200 adults only 166 could be mated. If 83 such pairs each 
averaged 3.8 juveniles, the 315 young thus produced (83 x 3.8) would 
TT 
