Type: report

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 2002. One hundred and two transient flycatchers of unknown subspecies were detected during surveys. Transients occurred in a range of habitat types including mixed willow riparian, willow-oak-sycamore dominated riparian, willow-cottonwood dominated riparian, riparian scrub and upland scrub. The distance from transient locations to the nearest surface water averaged 489  603 m (N = 101). Eighteen southwestern willow flycatcher breeding territories were located. With the exception of one territory at Lake O=Neill on Fallbrook Creek, all territories were along the Santa Margarita River, including a new site near the Base hospital, and one downstream of the concentration of birds between Rifle Range Road and Ysidora Basin. Ninety-four percent (17/18) of territories were located in mixed willow riparian habitat. Exotic vegetation, particularly and giant reed (Arundo donax), tamarisk (Tamarix ramosissima), and poison hemlock (Conium maculatum) was present in all territories, and was dominant (% cover > 50) in 11% (2/18) of territories. Resident flycatchers exhibited a bimodal distribution with regard to distance to surface water, with 60% within 70 m, and the remainder 100-900 m away from it. The resident flycatcher population included two non-territorial "floater" males, two unpaired males, and 16 pairs. Nesting was documented for all 16 pairs, which produced 1-2 nests each. Fifty-three percent (10/29) of nests were successful, and flycatchers fledged an average of 1.5 young per pair. No instances of cowbird parasitism were observed. Pairs placed nests in five species of plants, including black willow (Salix gooddingii), arroyo willow (S. lasiolepis), giant reed, tamarisk, and maiden's bower (Clematis ligusticifolia). Fourteen resident males and seven females were birds banded previously at Camp Pendleton between 1998 and 2001. Three birds (two males and one female) were immigrants from the San Luis Rey River. In addition, a male color banded in Costa Rica during the winter of 2001-2002 was resighted at the Base in July. Four resident males and four females were captured and color banded in 2002, and 10 nestlings in five nests were banded. None of the transients observed during surveys carried bands.