Wilson's Warbler (Wilsonia pusilla)
Associated Species: Other species that may use habitat in a similar way and/or respond similarly
to threats, management, and conservation activities include Broad-tailed Hummingbird,
MacGillivray's Warbler, Fox Sparrow, Song Sparrow, Lincoln's Sparrow, and White-crowned
Distribution: Wilson's Warblers breed throughout the Rocky Mountain West, and in a broad
band across Canada and Alaska. In Colorado they are fairly common summer residents in
mountain parks and higher mountains from 3000 to 4000 m (10,000-13,000 ft) in elevation.
Winter range includes northern Mexico south to Panama.
Habitat Requirements: These warblers nest in willow and alder thickets of stream banks, lake
shores, and wet meadows. They may be the most common breeding birds in Colorado's montane
and subalpine willow habitats (Andrews and Righter 1992).
Ecology: Wilson's Warblers arrive on breeding the breeding grounds in late May and lay eggs
soon after. Most young leave their nests by mid July. Fall migration begins in mid August.
Management Issues and Conservation Recommendations: Reduce or eliminate any activities
that degrade the structure and quality of willow shrub riparian systems. Do not permit timber
cutting within 30 m (100 ft) of the riparian area. Locate recreational facilities such as roads,
trails, and campgrounds away from riparian areas (Myers 1991).
Drawing down streams for agricultural, municipal, or other uses may degrade willow habitats.
Limit dewatering in areas where it could affect dense, extensive willow carrs.
Livestock grazing may remove ground cover, alter willow structure, and facilitate Brown-headed
Cowbird nest parasitism. Tightly control or eliminate livestock grazing in high elevation
Status and Reasons for Concern: Wilson's Warblers have a moderately high conservation need
throughout their range, and they have high representation in the physiographic area. Data for
BBS Physiographic Area 62 during 1966-1996 do not show a statistically significant annual rate
of change (P = 0.51; n = 22 routes). Wilson's Warblers were present on an average of 51.20%
(SE = 2.57) of BBS routes run in Physiographic Area 62 in Colorado, 1988-1997, at an average
abundance of 4.31 (SE = 0.37) individuals per route. The mean number of routes run each year
was 21.1 (SE = 3.06). This species is monitored by MCB with point transects.
Biological Objective: Maintain or increase Wilson's Warblers' distribution and abundance, with
progress toward meeting this objective based upon results of BBS and MCB monitoring
Selected References: Ammon 1995, Andrews and Righter 1992, Kingery 1998, Morrison 1981,