Violet-green Swallow (Tachycineta thalassina)
Associated Species: Other species that may use habitat in a similar way and/or respond similarly
to threats, management, and conservation activities include Purple Martins, Mountain Chickadees,
Pygmy and White-breasted Nuthatches, House Wrens, Mountain Bluebirds, and Western
Distribution: Violet-green Swallows breed from central Alaska south through the western
Canadian provinces and Rocky Mountain chain to southern Mexico, and from the Rocky
Mountain front west to the Pacific Ocean. In Colorado, they are fairly common breeding birds in
foothills, mountains, and mountain parks. They are common spring and fall migrants in western
valleys, and on eastern plains near foothills. They winter in central and southern coastal California
and southern Mexico.
Habitat Requirements: These swallows breed along the edges of aspen-dominated woodlands
or within open stands, on cliffs, and in cavities in riparian embankments. They also breed in lesser
numbers in open ponderosa pine and spruce-fir stands. They are obligate secondary cavity
nesters, using abandoned woodpecker cavities in snags, and natural cavities in cliffs and banks.
Breeding densities are directly related to snag density. Key habitat features are snags or live trees
containing cavities located near water or mountain parks.
Ecology: Violet-green Swallows arrive in Colorado in early March and begin breeding from mid
April through early May. They nest primarily in abandoned Red-naped Sapsucker and Downy
Woodpecker cavities, either singly or in small loose colonies; breeding site fidelity is high.
Breeding densities of 10-30 pairs per 40 ha (100 ac) have been reported, but densities are
dependent on availability of nesting cavities, which may vary widely across the landscape. Their
diet consists almost entirely of insects captured in flight as they forage over mountain parks,
riparian zones, reservoirs, moderate-sized forest openings, and within open forest canopies. Little
else is known about their behavior.
Management Issues and Conservation Recommendations: Populations of these swallows
depend directly upon the availability of appropriate nest cavities. Preferred nesting snags are of
decay class III, and located in open areas, along forest edges, or in open-structured stands.
Response to small aspen patch clearcuts within a matrix of uncut forest is either neutral or
positive. This species will readily accept artificial nest boxes, but House Wren predation may
reduce productivity in some habitats. Retain all live cavity-bearing trees and all large diameter
snags. Retain a minimum of 8-12 snags or live cavity-bearing trees per 4 ha (10 ac), and all
snags greater than 48 cm (19 in) dbh, especially those near water, riparian corridors, or stand
edges. Broken and spike-topped trees are also valuable retention trees. Maintain natural
disturbance regimes and the dynamic nature of aspen communities at the landscape scale.
Where natural disturbance mechanisms cannot be reintroduced, mechanical disturbance events
should mimic, as closely as possible, the disturbance history of the local area and surrounding
habitats. Sufficient snag and live cavity-tree densities should be maintained within commercial
Status and Reasons for Concern: This species has a moderately high conservation need
throughout its range, along with high representation in the physiographic area and an uncertain
population trend. Population trends of this species in Colorado are not adequately monitored by
the BBS, but populations appear to be stable at the continental scale. Abundance on BBS routes
in Colorado equals that of anywhere in the species range. They were present on an average of
89.64% (SE = 2.28) of the BBS routes run in Physiographic Area 62 in Colorado, 1988-1998, at
an average abundance of 22.57 (SE = 3.64) 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 the species' distribution and abundance, based upon
results of the BBS and MCB monitoring programs.
Selected References: Andrews and Righter 1992, Baicich and Harrison 1997, Dobkin 1994,
Ehrlich et al. 1988, Price et al. 1995, Yanishevsky and Petring-Rupp 1998.