Habits and Habitats of Mountain Plovers in California

Abstract

Continental populations of the Mountain Plover (Charadrius montanus) have declined drastically in the last quarter century. Despite many investigations of its breeding biology, the species has never been studied during the winter. Historically, most birds have wintered at lower elevations in inland California. We used radio telemetry to describe the movement patterns and habitats of plovers on the Pixley National Wildlife Refuge, Tulare County (1992-1993) and Carrizo Plain, San Luis Obispo County (1993-1994) of California. The first plovers were seen 7-20 October each year, with most birds arriving in early November. The daily survival rate for the 44 transmittered plovers was 0.9996 based upon 2,395 telemetry days of information. The calculated survival probability for the 1 November to 15 March winter period was 0.9474. Plovers foraged and roosted in loose flocks of 2 to >1,100 birds, with average flock size increasing late in the season at premigratory staging areas. Flock integrity was poorly developed as birds captured and telemetered together were, with one exception, not relocated together. The average minimum distance that the 44 plovers moved was 1.17 ± 1.42 km/day. Movements of individuals were highly variable due to the tendency of a bird to remain at a locale for a few days then move to a new area. Plovers moved >55 km between weekly relocations on seven occasions. The longest documented move was 127 km across the Temblor Mountains between 29 December 1993 and 5 January 1994. Site fidelity seemed poorly developed and the Carrizo Plain and southern San Joaquin Valley populations were considered biologically sympatric. Plovers at the Pixley NWR were usually relocated on contiguous croplands that had been recently cultivated. At both study areas, however, plovers preferred heavily grazed native rangelands. They used burned fields primarily for night roosting. Alkali flats, historically extensive but virtually nonexistent today, were the most favored habitat, where available. Flocks of plovers departed from California in mid-March each year and were recorded back on breeding areas in Colorado the third week of March. We conclude that plovers are being forced to use cultivated lands during winter in the San Joaquin Valley, and birds in relict populations at both locales are dependent upon core areas of native habitat in October and November especially.