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 July 2003. Thirty-nine transient flycatchers of unknown subspecies were detected during surveys. Transients occurred in a range of habitat types including mixed willow riparian, willowsycamore dominated riparian, riparian scrub, upland scrub and predominantly non-native vegetation. The distance from transient locations to the nearest surface water averaged 200 ? 399 m (N = 39). Twenty southwestern willow flycatcher territories were located. With the exception of two territories at Lake O’Neill on Fallbrook Creek and one territory upstream of Basilone Road on Las Flores Creek, all territories were along the Santa Margarita River. All territories were located in mixed willow riparian habitat. Exotic vegetation, particularly poison hemlock (Conium maculatum), giant reed (Arundo donax), and tamarisk (Tamarix ramosissima) was present in all territories, and was dominant (% cover > 50) in 10% (2/20) of territories. Eightyone percent of resident flycatchers were within 75 m of surface water, and the remainder 95-340 m away from it. The resident flycatcher population included six non-territorial “floater” birds, four unpaired males, and 16 pairs. Nesting was documented for all 16 pairs, which produced 1-3 nests each. Sixty-eight percent (17/25) of nests were successful, and flycatchers fledged an average of 3.0 young per pair. No instances of cowbird parasitism were observed. Pairs placed nests in ten species of plants, including black willow (Salix gooddingii), arroyo willow (S. lasiolepis), sandbar willow (S. exigua), mule fat (Baccharis salicifolia), stinging nettle (Urtica california), tamarisk, poison hemlock, wild rose (Rosa californica), coast live oak (Quercus agrifolia), and wild grape (Vitis girdiana). Ten territorial males, 11 territorial females, and three floaters were banded previously at Camp Pendleton between 2000 and 2002. Fifty-five percent of the adults banded in 2002 returned in 2003, while 27% of nestlings and hatching year birds banded in 2002 returned to Camp Pendleton in 2003. Thirty-three percent of returning adults changed breeding locations within Camp Pendleton between 2002 and 2003. Six resident males and two females were captured and color banded in 2003, and 34 nestlings in 12 nests were banded. None of the transients observed during s