Darkness comprises more than half of each 24-hr cycle during winter in California’s Sacramento Valley, but no studies have assessed nocturnal habitat use by wintering shorebirds at this inland site. From February to May 2013, the day and night habitat associations of radio-tagged Dunlin (Calidris alpina) were compared between post-harvest flooded rice fields and managed freshwater wetlands in the Sacramento Valley. Dunlin had decreasing associations with rice during both day and night from February to April. Dunlin exclusively used rice at night until 25 March, when they shifted to wetlands. During the day, Dunlin were regularly associated with both rice and wetlands until 4 March, and they exclusively used wetlands beginning 25 March. Diel movements by individual Dunlin revealed that birds using rice during the day also used rice during the subsequent night. Our findings suggest that flooded rice, when available, may be more suitable as nocturnal habitat than managed wetlands, and the removal of water from rice fields in February and March causes Dunlin to either use wetlands exclusively or leave the area. Conservation of Dunlin, and likely other migratory shorebirds, may be enhanced by managing the agriculture-wetland mosaic in the Sacramento Valley to ensure that an adequate amount of shallow-water habitats remain during March and April, prior to spring migration.
PUBLICATION AVAILABLE AT: http://doi.org/10.1675/063.038.0106