Geoscience Reference
In-Depth Information
EXAMPLE 8.2 Recoveries of Male Wood Ducks
Brownie et al . (1985, p. 14) give an example of banding and recovery data
for male wood ducks ( Aix sponsa ) banded before the hunting seasons in
1964 to 1966 in a midwestern state in the United States, with recoveries of
dead ducks recorded for 1964 to 1968. The recovery data are reproduced
here in Table 8.6 together with the derived statistics R j , C j , and T j .
From Equation (8.14), it is found that
ˆ 1 = (265 × 127)/(1603 × 265) = 0.0792,
so that it is estimated that bands were recovered from 7.9% of the birds
that died in 1964. From Equation (8.16), the estimated variance is
· f
Var( ˆ 1 = 0.0792²(1/265 - 1/1603 + 1/127 - 1/265) = 0.00004548
giving an estimated standard error of 0.00004548 = 0.0067. An approxi-
mate 95% confidence interval for the true recovery rate is therefore
0.0792 ± 1.96 × 0.0067 or 0.066 to 0.092 (6.6% to 9.2%). Similar calculations
for the other recovery rates give ˆ 2 = 0.0401 with standard error and 95%
confidence limits of 0.032 to 0.048, and ˆ 3 = 0.0688 with standard error
0.0061 and 95% confidence limits of 0.057 to 0.081. From Equation (8.15),
it is found that
S ˆ 1 = (265/1603) (1 - 127/265) (1596/211) = 0.651,
so that it is estimated that 65.1% of ducks alive at the start of 1964 sur-
vived that year. From Equation (8.17), the estimated variance is
· S
Var( ˆ j = 0.651²{1/265 - 1/1603 + 1/210 - 1/1595 +
1/(348 - 210) - 1/265 = 0.004556,
giving an estimated standard error of 0.004556 = 0.0675. An approx-
imate 95% confidence interval for the population survival rate is then
TABLE 8.6
Banding and Recovery Data for Male Wood Ducks Banded before the
Hunting Seasons in a Midwestern State in the United States
Recoveries of Dead Ducks in
Year of
Release
Number
Released
R, Total
Recovered
1964
1965
1966
1967
1968
1964
1603
127
44
37
40
17
265
1965
1595
62
76
44
28
210
1966
1157
82
61
24
167
C , year total
127
106
195
145
69
T (see text)
265
348
409
214
69
 
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