Type: report

Article abstract: Surveys for the endangered southwestern willow flycatcher (Empidonax traillii extimus) were conducted at Marine Corps Base Camp Pendleton, California, between 13 May and 1 August 2008. Fifty-five transient flycatchers of unknown sub-species were observed during Base-wide surveys. Transients occurred on 10 of the 16 drainages surveyed in 2008. No willow flycatchers were detected at Cockleburr, Cristianitos, French, Newton, Roblar, or Windmill Creeks. Transients occurred in a range of habitat types including mixed willow riparian, willowsycamore dominated riparian, oak-sycamore dominated riparian, riparian scrub, and upland scrub. The distance from transient locations to the nearest surface water averaged 363 ± 472 m (std, n = 55). In 2008, the resident southwestern willow flycatcher population on Base consisted of seven females, seven males, and one non-territorial “floater” bird. Nine territories were established, consisting of seven pairs and two single males. In total, seven females formed pair bonds with five male willow flycatchers. Two of the five paired males were polygynous with two females each. All territories were located in mixed willow riparian habitat. Poison hemlock (Conium maculatum) was present in all territories. Distance to surface water averaged 73 ± 39 m (std, n = 10), with 70% (7/10) of resident flycatchers located within 100 m of water. Eight nesting attempts by willow flycatchers were documented during the 2008 breeding season. Nesting was initiated in late May and continued into August. Eighty-eight percent (7/8) of nests successfully fledged at least one flycatcher young. Predation accounted for the one nest failure. Of the seven pairs whose nests were monitored, 100% (7/7) fledged young. Twenty fledglings were produced, yielding an estimated seasonal productivity of 2.9 young per pair (20 young/7 pairs). No instances of brown-headed cowbird (Molothrus ater) parasitism were observed. Pairs placed nests in five species of plants, including black willow (Salix gooddingii), arroyo willow (S. lasiolepis), sandbar willow (S. exigua), mule fat (Baccharis salicifolia), and poison hemlock. Eighty-eight percent of nests were placed in native species. Seven resident females and five males that were banded in previous years were present at Camp Pendleton in 2008. Of the banded adult flycatchers present during the 2007 breeding season, 67% (4/6) of males and 13% (1/8) of females returned to Camp Pendleton in 2008. Si