Northern Prairie Wildlife Research Center
The recapture rate of 0.196 for web-tagged mallard nestlings divided by the return rate of 0.288 for nasal-marked mallard young ( age = 44.6 days) yielded an estimated survival of 0,681 for the interval (Table 12). Survival of gadwall ducklings between the nestling stage and mean age of 33.8 days was estimated at 0.828 employing the same mathematics used for mallards.
|Table 12. Comparison between recapture rates of web-tagged nestlings and return rates of nasal-marked mallard and gadwall female ducklings on the Koenig study area, North Dakota, 1976-81.|
|Mean age (days)||No. of hens marked||No. recaptured
or return rate
|a Assumes that 50% of ducklings marked with web tags were hens.|
We web-tagged 325 ducklings at 43 successful mallard nests of which 31 hens were eventually recaptured in a subsequent year (Table 13). Only 10 of these recaptures represented a single individual from a clutch, which was significantly less ( = 3.09, 1 df, P = 0.07) than the 15.54 single recaptures expected. Gadwall nestlings were web-tagged at 50 successful nests from which 23 hens were eventually recaptured and identified. Eight of these recaptures involved a single individual from a clutch, which was significantly less ( = 2.99, 1 df, P = 0.08) than the 13.45 single recaptures expected. When we combined data from mallards and gadwalls, we found significantly fewer ( = 6.09, 2 df, P = 0.05) broods than expected had a single individual recaptured.
|Table 13. Calculations of the probability that recaptures of web-tagged mallard nestlings were independent of brood mates.|
|No. of marked young/clutch (n)||No. of broods with n marked||Probably of young recapture (Zn)||No. of broods from which a single young was recaptured|
|Expected no.||Observed no.|