238


term decline in the Wood Stork population, providing the

average yearly survival rate of birds that have passed

their first year is 90% and the female fledgling production

rate per successful nest is 1.4, or one-half of Kahl's

(1963) estimate of 2.8 male and female fledglings per

successful nest. The table shows the effect of different

fledgling (leaving the nest to age 1) survival rates in

different years. With an average fledgling survival rate

of 60, successful nesting is necessary only once every 5

to 6 yrs, but an average fledgling survival rate of 20%

requires that the birds have a successful nesting season

every 1 or 2 yrs. The average number of female fledglings

that must be produced per year per female to prevent a

long-term decline in population ("b") varys from 0.24 with

60% fledgling survival to 0.72 with 20% fledgling survival.



Estimated Female Fledgling Production Rates at Corkscrew

 Table 30 gives estimates of the actual average number

of female fledglings produced per breeding female per year

at Corkscrew Swamp sanctuary for the total period of record

(1956-57 through 1974-75), for the first 8 yrs of record,

and for the last 11 yrs of record. Comparison of these

figures with the "b" values in Table 29 indicates a stable

population during the first 8 yrs, even under the worst

(20%) tested fledgling survival rates, but a declining

population during the last 11 yrs at even the best (60%)

tested fledgling survival rate. Actual fledgling survival