MacGillivray's Warbler (Oporornis tolmiei)
Associated Species: Other species that may use habitat in a similar way and/or respond similarly
to threats, management, and conservation activities in foothills shrublands include Broad-tailed
Hummingbird, Virginia's Warbler, Spotted Towhee, and Green-tailed Towhee. In willow carr
ecosystems, associated species include Broad-tailed Hummingbird, Dusky Flycatcher, Yellow
Warbler, Wilson's Warbler, Fox Sparrow, Lincoln's Sparrow, and White-crowned Sparrow.
Distribution: MacGillivray's Warblers breed throughout western North America. In Colorado
MacGillivray's Warblers are uncommon to fairly common summer residents in the foothills and
lower mountains from 1800 to 3400 m (6,000-11,000 ft) in elevation. They are most numerous
in the lower mountains. They winter from west and central Mexico to Central America.
Habitat Requirements: MacGillivray's Warblers nest in foothills and mountain shrubland and
willow carrs. They also breed in moist aspen forests with shrubby understory, in shrubby forest
openings, and in Gambel oak in moist ravines.
Ecology: These warblers arrive on their breeding grounds in early to late May. They lay eggs in
early to late June, and most young leave the nest by late July. Fall migration begins in mid
September. The diet consists exclusively of insects.
Management Issues and Conservation Recommendations: Reduce or eliminate any activities
that degrade the structure and quality of the overstory or understory of these riparian systems.
Timber cutting should not be permitted within 30 m (100 ft) of the riparian area. Domestic
livestock grazing should be tightly controlled or eliminated in these areas. Summer grazing
should not be permitted. Recreational facilities such as roads, trails and campgrounds should
be located up, out of riparian areas (Myers 1991).
Status and Reasons for Concern: MacGillivray's Warblers are representative of many other
species in the montane riparian habitat type because they occupy habitat typically used by other
species. Data for BBS Physiographic Area 62 during 1966-1996 do not show a statistically
significant annual rate of change (P = 0.41; n = 27 routes). This species was present on an
average of 52.08% (SE = 3.91) of routes run in Physiographic Area 62 in Colorado, 1988-1997,
at an average abundance of 2.43 (SE = 0.34) individuals per route. The mean number of routes
runs each year was 21.1 (SE = 3.06). This species is monitored by MCB with point transects.
Biological Objective: Maintain or increase the species' distribution and abundance, based upon
results of the BBS and MCB monitoring programs.
Selected References: Andrews and Righter 1992, Kingery 1998, Pitocchelli 1995.