BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Sialia currucoides | Mountain Bluebird 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Spring Migration:  Mountain bluebirds and western bluebirds arrive in
south-central Washington at the same time of year (February to March) in
mixed flocks with approximately equal sex ratios [29].  Power [46]
however, reported that males usually arrive on Montana breeding grounds
first, from only few days to as many as 30 days before the females.  The
median arrival date for males was April 8; for females, April 25 [46].
In southwestern Manitoba mountain bluebirds usually arrive in late March
[37].  In Zion National Park mountain bluebirds are summer residents
above 8,000 feet (2,438 m) elevation but move to lower elevations in
winter [8].
 
Nest Site Selection and Territory Defense:  Mountain bluebird territory
type is Berger's type A:  a large breeding area where courtship,
copulation, nesting, and food seeking occur.  In south-central
Washington western bluebirds select and defend nest boxes soon after
arrival but mountain bluebirds continue to prospect.  Mountain bluebirds
make nest box selection about 2 weeks after western bluebirds have
established territory but mountain bluebird nest-building activity peaks
1 week earlier than that of western bluebird [29].  Mountain bluebirds
and western bluebirds exhibit interspecific territoriality, as do
mountain bluebirds and eastern bluebirds in areas of sympatry [45].
Interspecific attempts at displacement of resident birds at nest boxes
are not usually successful [29].  In Montana pairs using nest boxes on
fenceposts or utility poles mostly stayed along the fence or utility
line and its immediate vicinity.  The smallest territory was 100 yards
(91 m) wide.  Some territories had no clear boundaries [46].

Clutch Size and Incubation:  Typical mountain bluebird clutch size is
five or six eggs (range 3-8) [8,18,29].  Incubation, usually by the
female, lasts 13 to 14 days [18].  Some of Bent's [8] contributors
observed occasional incubation by the male.

Development of Young:  Mountain bluebird hatchlings are altricial,
blind, and without feathers.  Natal down appears on the second day.
Eyes begin to open by the fourth or fifth day.  Mountain bluebird
nestlings are fed by both parents but usually only brooded by the
female.  Mountain bluebirds fledge at about 22 to 23 days but are not
independent of parental feedings until 22 to 28 days after fledging
[18].

Double-Brooding:  Mountain bluebirds often raise a second brood in the
same season [29].

Fall Migration:  In Manitoba mountain bluebirds usually stay through
late October [37].  In Montana large flocks of mountain bluebirds gather
from October to November.  These flocks usually stay together during
seasonal movements and over the winter [46].


PREFERRED HABITAT : 
Mountain bluebirds normally occupy open woodland or edge habitat with
exposed perches and fairly sparse ground cover [29,45].  They are
attracted to burned areas, particularly with dead trees and/or snags
present [32,39,40].  For more information on the relationship of
mountain bluebirds to postfire environments see FIRE EFFECTS AND USE.
Hutto and others [33] listed 19 studies reporting increased mountain
bluebird populations in partially cut or clearcut forests.  In northern
Arizona ponderosa pine stands, mountain bluebirds were present on
clearcut sites but not in light, medium, and heavily cut stands or in
uncut stands [60].

In Utah mountain bluebirds are common summer residents of high valleys;
they are uncommon winter visitors to lower valleys in southern Utah [25].


COVER REQUIREMENTS : 
Nesting:  Mountain bluebirds often use abandoned woodpecker (Picidae)
holes in dead or dying trees as nest holes [32,45].  Other cavities used
for nesting include holes in dirt banks, abandoned swallow (Hirundae)
nests, American dipper (Cinclus mexicanus) nests, hollow fenceposts,
mailboxes, holes in buildings, and nest boxes [29].  Crevices in cliffs
and mesas are also used [45].  Entrance hole orientation does not affect
nest site use [44].  In western Montana mountain bluebirds use whitebark
pine snags for nest sites at high elevations.  At lower elevations
western larch (Larix occidentalis) snags are preferred, even though
Douglas-fir and lodgepole pine (Pinus contorta) snags are more abundant.
Preferred sites are open or semi-open.  Average diameter of four snags
used by mountain bluebirds was 23 inches (58 cm); snag diameters ranged
from 10 to 29 inches (25.4-74 cm) [40].  In Wyoming mountain bluebirds
used an abandoned American dipper nest on the underside of a bridge.
Mountain bluebirds frequently nest in river banks in the area [14].

Nest Boxes:  In south-central Washington mountain bluebirds used nest
boxes 0.3 mile (0.5 km) or more from ponderosa pine-Oregon white oak
(Quercus garryana) stands, but also used nest boxes near trees.  They
showed less of a preference for nest box location than western
bluebirds, which always used boxes near trees or other cover [29].

Foraging:  Perches near open, well-lighted areas with sparse ground
cover are favored foraging sites.  Dead branches are preferred to living
ones, presumably for greater prey visibility.  Where natural vegetation
is tall, mountain bluebirds prefer mowed to unmowed areas.  Areas with
dry, nonfertile soils, low vegetation, and much bare ground are
preferred.  Mountain bluebirds forage farther from perches than the
other two bluebird species and are occasionally found in open areas with
low perch densities [45].


FOOD HABITS : 
Mountain bluebirds are primarily insectivorous, but also consume fruit
when insects are inactive (in early morning and in the cooler seasons).
Contents of 66 adult mountain bluebird stomachs were 92 percent animal
matter, which was 30 percent beetles, 23 percent grasshoppers, 14.5
percent caterpillars, 13 percent ants, 8 percent weevils, 4 percent bees
and wasps, 4 percent true bugs, and less than 1 percent flies [7].

Insect Prey:  In south-central Washington, beetle consumption decreased
during the nestling period.  Nestling foods are mostly grasshoppers,
crickets, and caterpillars [29].

Plant Foods:  Mountain bluebirds eat mistletoe (Phoradendron spp.),
hackberry (Celtis spp.), Saskatoon serviceberry (Amelanchier alnifolia),
and buffaloberry (Shepherdia spp.) berries in the nonbreeding season
[61].

Foraging Strategies:  Mountain bluebirds adjust foraging strategies to
habitat and ground vegetation conditions [45].  Mountain bluebirds
usually forage from elevated perches.  When prey is spotted a mountain
bluebird drops to the ground to capture it [29].  Mountain bluebirds
hover in search of prey and have been observed foraging on the ground
(hopping-gleaning) in grazed valleys with sparse vegetation [45].


PREDATORS : 
Mountain bluebirds are preyed upon by many raptors including Cooper's
hawk (Accipiter cooperi), red-tailed hawk (Buteo jamaicensis),
sharp-shinned hawk (A. striatus), northern harrier (Circus cyaneus), and
possibly American kestrel (Falco sparverius).  In addition, American
crow (Corvus brachyrhynchos) may prey on eggs, nestlings, and adults.
Adult mountain bluebirds are sometimes killed by house sparrows (Passer
domesticus) in competition for nest sites; a deer mouse (Peromyscus
maniculatus) was suspected in the death of an adult female mountain
bluebird whose nest box she had usurped.  Deer mice destroy eggs and
nestlings in nest boxes, as do eastern chipmunks (Tamias striatus) and
red squirrels (Tamiasciurus hudsonicus).  Nestlings have also been
destroyed by infestations of ants [37].


MANAGEMENT CONSIDERATIONS : 
Population Status and Trends:  In the early 1900's the range of mountain
bluebird expanded east into the Great Plains [45].  Herlugson [28]
suggested that in this century, mountain bluebird has replaced western
bluebird as the predominant bluebird in the Northwest.  Changes in
relative abundance of mountain bluebird and western bluebird in areas of
sympatry are probably caused by changes in the openness of the
landscape.  Grazing reduces herb density and may benefit mountain
bluebird at the expense of western bluebird.  Mountain bluebird probably
benefits more from logging than either eastern or western bluebird [45].
In Arizona Szaro [58] recorded the replacement of western bluebird by
mountain bluebird following clearcutting in ponderosa pine forests.
Sharp [54] indicated that mountain bluebird populations increased in
juniper woodlands in Oregon between 1899 and 1983.  Johnson [34]
reported an increasing trend for mountain bluebird in Nevada between
1939 and 1973.  DeSante and George [16], however, listed mountain
bluebirds as decreasing in Alberta and Nevada in the last 100 years.  In
northern Idaho populations of secondary cavity nesters including
mountain bluebird have been declining since the early 1970's as
suitable breeding areas are lost to agricultural expansion [67].  Hejl
[26] hypothesized that species associated with burns and/or snags, such
as mountain bluebird, are less abundant than they were 100 years ago;
nest site availability is a limiting factor in mountain bluebird
productivity [29].

Nest-site Competition:  Interspecific competition for nest cavities has
probably contributed to the decline of some mountain bluebird
populations in this century.  Primary competitors include northern
flicker (Cloaptes auratus), swallows, and, since their introduction from
Europe, house sparrows and European starlings (Sturnus vulgaris)
[18,29].  Competition with European starlings for nest sites has
probably contributed to mountain bluebird population decline in Utah
[25].  Nest boxes in south-central Washington are used by other species
including violet-green swallows (Tachycinera thalassina), deer mice, and
yellow-pine chipmunks (Tamias amoenus) [29].  Other nest-site
competitors include eastern and western bluebirds in areas of sympatry,
particularly in the Great Plains grasslands where eastern and mountain
bluebirds have expanded their ranges [45].

Management Recommendations:  Mountain bluebirds prefer open habitats;
throughout their range they are always more abundant in recent clearcuts
than in uncut forest [27].  In northern Utah mountain bluebirds were
visitors on quaking aspen study sites prior to timber harvest but
returned as breeders to clearcut areas.  Apparently, clearcutting small
patches provides more open habitat adjacent to uncut forest; this
improves foraging habitat for mountain bluebirds while retaining
sufficient numbers of cavities for nesting [15].  Also in Utah mountain
bluebirds were only observed in a 17-year-old clearcut that had been
bulldozed and broadcast burned after harvest.  At the time of the census
the stand consisted of lodgepole pine about 6 to 15 feet (1.8-4.6 m)
tall with a moderately dense, forb-dominated ground cover.  Mountain
bluebirds were not observed in a 37-year-old clearcut, mature forest,
stagnated forest, wet meadow, or dry meadow [5].  An unpublished report
described by Astroth and Frischknecht [3] indicated that mountain
bluebirds declined immediately after removal of pinyon (Pinus
spp.)-juniper woodlands (for range improvement) but returned to
pretreatment levels in 1 year.  Szaro and Balda [59] suggested that for
northern Arizona ponderosa pine communities, removal of one-sixth to
two-thirds of available foliage either in strips or by thinning is not
detrimental to breeding bird communities in terms of species richness,
density, or diversity.  The species present in disturbed communities
are, however, different from those of undisturbed communities.

Any management plan should consider the importance of snags for wildlife
[39].  Hutto [32] emphasized the importance of snags for cavity nesters.
It is generally recommended that all natural snags be left during timber
harvest operations unless they pose immediate safety hazards [32,45,52].
Mature and decadent living trees should be left as well to provide snags
in the future [45].  Salvage cutting of burned forest is detrimental to
cavity nesting species, particularly woodpeckers and secondary cavity
nesters such as mountain bluebirds [32].  McClelland and others [40]
recommend leaving old-growth components within harvested areas.  For
example for every 1,000 acres (405 ha) management unit, they recommended
leaving 50 to 100 acres (20-40.5 ha) uncut (old growth) for wildlife
feeding areas; on the remaining acreage logs, snags, and cull trees
should be left.  Firewood cutting should be limited to snags less than
15 inches (38 cm) d.b.h. [40].

Nest Box Programs:  Nest boxes resulted in a substantial increase in
breeding mountain bluebird densities in northern Idaho study plots [67].
In south-central Washington nest box placements have also resulted in
breeding density increases.  Nest box fidelity is fairly high,
particularly among successful breeders (68.2%).  Unsuccessful breeders
(5 individuals in this study) had a lower rate of nest box fidelity:
two used the same box, one changed territory but not box type, and two
changed territory and box type [30].  Nest boxes for mountain bluebirds
in southwestern ponderosa pine forests should be placed along forest
edges or in grassy glades within open forests.  Mountain bluebirds use
large nest boxes with 3-inch (7.6 cm) holes if no other sites are
available [21].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Sialia currucoides | Mountain Bluebird