|Abstract or Summary
- Avian movement behavior provides insight on patterns of regional and local
fidelity, habitat and resource requirements, the scale at which individuals perceive
the landscape, and the relative influence of the spatial array of resources.
Shorebirds (suborder: Charadrii) are a diverse and mobile group of wetland
associated species. Large numbers of shorebirds utilize seasonally flooded wetland
habitats in the Willamette Valley of northwest Oregon; however, there is little
information on fidelity and movements of birds in the region or at other inland
sites. Thus, we quantified winter fidelity and movement patterns of radio-tagged
Dunlin (Calidris alpina) and Killdeer (Charadrius vociferus) in the Willamette
Valley in 1998-1999 and 1999-2000.
Prior to field telemetry, we evaluated use of a leg-loop harness design for
attachment of radio-transmitters. Comparisons between captive Western
Sandpipers (Calidris mauri) fitted with a harness package and a control group
indicated no significant differences in behavior. In addition, observations of wild
Killdeer and Dunlin indicated prolonged harness retention and no adverse effects
on behavior. Therefore, we determined that the modified harness design was a
suitable method for attachment of transmitters to shorebirds.
Monitoring of radio-tagged Dunlin and Killdeer indicated interspecific
differences in regional fidelity and residency patterns. Dunlin exhibited a high
degree of regional fidelity and in most cases remained within the Valley for the
duration of the winter. In contrast, Killdeer departed the study area throughout the
winter and the population segment monitored was composed of winter residents
(63%), winter transients (26%) and year-round resident breeders (11%).
Dunlin were highly mobile with frequent movements up to 30 km from
roost sites. Among seasons, Dunlin differed significantly in distance traveled,
mean distance from capture site, and home range size. All were greatest during late
winter. In comparison, the scale of Killdeer movements was much smaller, with no
seasonal differences in movements. Results also suggested that resident Killdeer
were more sedentary than migrants during the winter months. At a local scale,
individuals of both species occurred predominantly in agricultural habitats and
exhibited low degrees of fidelity to specific fields, with the exception that Dunlin frequently returned to certain roost sites. On a daily basis, movements of both
Dunlin and Killdeer were most pronounced during crepuscular periods.
Findings provide insight on the fidelity and winter movements of
shorebirds, as well provide insight as to the functional connectivity of shorebird
habitats in the Willamette Valley.