Abstract:
Although widely studied in many portions of North America, little is known
about the specific habitat requirements of mallard ducks (Anas platyrhynchos) during
the breeding season in western Oregon. I radio-marked 72 female mallards in the
Willamette Valley of Oregon in March-April 1995-96 to document wetland habitat
selection during pre-nesting and nesting phases, nesting cover selection, nesting and
female success rates, nesting chronology, and survival of females during the pre-nesting
and nesting periods. Wetland habitat selection was higher for seasonal
riverine and permanent lacustrine habitats during the pre-nesting and nesting periods.
Uncultivated upland and wetland habitat nesting sites with a strong cover component
had a higher selection ranking compared to agricultural cropland and ash-cottonwood
riparian. The reproductive period was 107 days beginning in early-March and
concluding in late-June with the peak of nest attempts occurring around May 9.
Nesting effort was low with 38.4% of females failing to attempts at least one nest.
Nest survival probabilities ranged from 0.106 in 1995 to 0.216 in 1996 with a pooled estimate of 0.186 (95% C.I.=0.122-0.298). Mammalian predation accounted for 84%
of nest failures. Overall female success was 40.5% and differed between first year
(SY) and second year and older females (ASY). Female survival probabilities ranged
from 0.5 11 in 1995 to 0.733 in 1996, with a pooled estimate of 0.668 (95%
C.I.=0.5370.842).
