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Mallard Recruitment in the Agricultural Environment of North Dakota

Brood Survival

The survival of broods from hatching to fledging is an important component of recruitment. We attempted to estimate the survival of at least 1 brood member from hatching to the first observation on water and also the average size of broods at fledging. Various measurement problems and biases associated with these variables were discussed in detail by Cowardin and Johnson (1979). Our data on this subject are limited because nest success was low and, as a result, our sample of broods was small. In addition, we had difficulty detecting the presence of a brood and counting the number of young because hens frequently took young to ponds dominated by dense stands of whitetop rivergrass (Scolochloa festucacea) or tule bulrush.

Survival of Broods

Survival of broods from nest to water was 74.1% in 1977-80 (Table 18). Cowardin and Johnson (1979) summarized brood survival data from several previous studies and used an estimate of 70% for estimating annual rate of change in mallard populations. Talent et al. (1983) estimated that 48% of mallard brood hens fledged at least 1 duckling. Their study was conducted on areas just south of ours from 1976 to 1977. They also estimated that 85% of the duckling mortality occurred within the first 2 weeks. Our estimate of survival from nest to first observation is more comparable to 56% (48% ÷ 0.85) based on their data. Even with correction our estimate should exceed theirs because our broods were observed <2 weeks after hatching.

Table 18. Broods in which at least 1 duckling survived from hatch to the first observation on water.
Year Number of successful nests Surviving broods Survival rate (%)
1977 3 2 66.7
1978 10 7 70.0
1979 6 4 66.7
1980 8 7 87.5
All years 27 20 74.1

We were not able to determine whether brood mortality occurred on water or on the initial overland move. Talent et al. (1983) suggested that loss of entire broods frequently occurred on water as a result of mink predation. Two of our brood hens were killed by mink. Sargeant et al. (1973) found that 28% of young wood ducks (Aix sponsa) placed in floating pens were later recovered in mink dens.

Distance Moved by Broods

Ball et al. (1975) found a negative correlation between distance moved overland by young broods and survival of young. Talent et al. (1983) did not find evidence of loss during overland moves. Our data are not sufficient to construct such a correlation, but we did document the magnitude of 20 initial moves. Mallard hens made moves ranging from 63 to 3,780 m (median 862 m, N = 20) from the nest to the wetland where broods were first observed, usually within 1 week of hatching. Actually these moves may represent a series of overland moves between several ponds. Our telemetry locations suggested that some hens moved broods down small drainages. The mean distance to the nearest wetland at hatch was 160.5 m for successful nests, which suggests that mallard hens are selective in choosing wetlands for broods and often do not go to the nearest wetland. It seems reasonable to assume that there is some risk of mortality of young ducklings making these lengthy overland moves.

Average Brood Size

We found that our techniques were not adequate for determining average brood sizes because we were seldom able to get reliable counts of entire broods following radio-marked hens. For estimating overall recruitment rate and modeling change in population size (below), we used a fledged brood size of 4.9 (Cowardin and Johnson 1979). In our opinion, survial of young from hatch to fledging is probably the least understood component of recruitment. Furthermore, present methodology for assessing brood survival is not adequate for obtaining large samples. It also requires that the brood be observable. Future development may permit radio marking of individual brood members, thus permitting calculation of daily mortality rates for ducklings.
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