Article abstract: Surveys for the endangered southwestern willow flycatcher (Empidonax traillii extimus) were conducted at Marine Corps Base Camp Pendleton, California, between 15 May and 31 August 2000. Eleven transient flycatchers of unknown subspecies were detected during surveys, and two transients were captured in mist nets at MAPS (Monitoring Avian Productivity and Survival) stations on De Luz Creek and the Santa Margarita River. Transients occurred in a range of habitat types including mixed willow riparian, willow-sycamore dominated riparian, and sandbar and mule fat scrub. All but one transient individual were sighted within 50 m of surface water. Eighteen southwestern willow flycatcher breeding territories were located. With the exception of a new site at Lake O'Neill on Fallbrook Creek, all territories were along the lower Santa Margarita River. The majority of territories (15/18) were located in mixed willow riparian habitat. Resident flycatchers exhibited a bimodal distribution with regard to distance to surface water, with 53 percent within 50 m, and the remainder from 150 to 575 m away from it. The eighteen territorial males included ten confirmed pairs, five single males, and three males of undetermined status. Nesting was documented for eight of the ten pairs, with each pair attempting one nest. All nests were successful, and flycatchers fledged an average of 2.3 young per pair. No instances of cowbird parasitism were observed. Pairs placed nests in five species of plants, including black willow (Salix goodinggii), sandbar willow (S. exigua), stinging nettles (Urtica dioica), blackberry (Rubus ursinus) and giant reed (Arundo donax). Two resident males and one female were returning banded birds, including one male banded as an adult in 1998 and one female banded as an adult in 1999. Four resident males and one female were captured and color banded in 2000, and six nestlings in two nests were banded. In addition, both of the transients captured at MAPS stations were banded. None of the transients observed during surveys carried bands.
Number of pages: 39
Authors: Kus, Barbara;
Prepared for: Assistant Chief of Staff, Environmental Security U.S. Marine Corps Base Camp Pendleton;
Prepared by: U.S. Geological Survey, Western Ecological Research Center; Kus, Barbara;
Keywords: endangered species; Marine Corps Base Camp Pendleton; southwestern willow flycatcher;
Species: Southwestern willow flycatcher