Sialia mexicana is found throughout parts of western North America, including southeastern British Columbia, Alberta, Washington, Oregon, Idaho, California, Nevada, Utah, Colorado, New Mexico, Arizona, northern Baja California, and the central Mexican states.

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Breeding range includes western North America from southern British Columbia and southwestern Alberta south to northern Baja California and the Central Volcanic Belt of Mexico, excluding most of the Great Basin. Breeding range in the United States extends east to Wyoming, Colorado, New Mexico, and western Texas. Winter range includes the breeding range (typically at lower elevations) in southern British Columbia, western Oregon, California, Baja California, southwestern Nevada, and from central Utah and portions of central Colorado and New Mexico south. Western bluebirds also winter in areas outside the breeding range in California, Baja California, Arizona, New Mexico, westernmost Texas, and throughout much of northern Mexico.

Western bluebirds are small thrushes ranging in length from 16.5 to 19 cm and weighing from 24 to 31 g. Male and female adult western bluebirds differ in their coloration. The females are less dramatic than the males. They tend to have a brown abdomen and a gray head, throat and back. Their tails and wings are a gray-blue color. The males are brighter. Cobalt-blue is found on their head, chin, throat, and tail. The males have a brown breast and a gray-blue belly. Juveniles exhibit the same patterns as adults, except their coloration is not as intense.

Range mass: 24 to 31 g.

Range length: 16.5 to 19 cm.

Sexual Dimorphism: sexes colored or patterned differently; male more colorful

Average basal metabolic rate: 0.423 W.

Length: 18 cm

Weight: 29 grams

See Kaufman (1992) for detailed information on identification of bluebirds.

• Terrestrial

Western bluebirds are often found at the edges of forests. Because of the availability of perch sites, they tend to live in burned and logged areas. Western bluebirds tend to build their nests in conifer trees (pine and firs) and deciduous trees (oak). They do not live in open areas, such as meadows. They can be found at elevations up to 2,900 m.

Range elevation: 2,900 (high) m.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: forest ; scrub forest

Comments: Habitat includes open woodlands, farmlands, orchards, savanna, riparian woodlands, and burned woodlands, also deserts in winter. Nests are in natural tree cavities, abandoned woodpecker holes, or bird nest boxes, usually 5-40 feet (1.5-12 meters) above ground.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Western bluebirds may wander/withdraw from northern breeding areas during the winter. Some move to higher elevations in fall.

Western bluebirds eat a variety of foods; their main food source varies depending on the season. During the spring and summer months, they are insectivorous. They are "perch-foragers" at this time; they will look for prey from a perch and then drop down on the ground to pick it up. During the winter, western bluebirds mainly eat fruit. Their main source of food in the winter is mistletoe berries (Phoradendron).

Foods eaten include: spiders, flies, grasshoppers, bees, sowbugs, beetles, termites, mistletoe berries, cherries, blackberries, raspberries and figs.

Animal Foods: insects; terrestrial non-insect arthropods

Plant Foods: fruit

Primary Diet: omnivore

Comments: Mainly insectivorous; feeds on grasshoppers, caterpillars, beetles, etc. Also eats other invertebrates (spiders, earthworms, sow bugs, etc.). Feeds seasonally on berries and other fruit. Forages by flycatching and by dropping from perch to ground.

Western bluebirds live in areas that are occupied by other birds. Conflicts arise between swallows, wrens, woodpeckers, and flycatchers for nest space and food. Swallows and wrens have taken over some western bluebird nest sites because space is limited. Western bluebirds and mountain bluebirds have overlapping ranges, but western bluebirds establish their nests earlier, so they usually win disputes over nesting sites.

Chipmunks (grey-necked chipmunk (Eutamias cinereicollis), townsend chipmunk (Eutamias townsendii) and yellow-pine chipmunk (Eutamias amoenus)), squirrels (Douglas squirrel (Tamiasciurus douglasi), red squirrel (Tamiasciurus hudsonicus) and tufted-eared squirrel (Sciurus aberti)) and mice (deer mouse (Peromyscus maniculatus)) are predators of western bluebirds. They will attack chicks in a nest and then take over and live in the nest. Male western bluebirds stand guard at the nests and chase intruders away. While an intruder is running away, the male will grasp the intruder's legs causing it to fall. Then, the bird will attack the predator with his beak.

Known Predators:

• grey-necked chipmunks (Tamias cinereicollis)
• Townsend's chipmunks (Tamias townsendii)
• yellow-pine chipmunks (Tamias amoenus)
• Douglas's squirrels (Tamiasciurus douglasii)
• red squirrels (Tamiasciurus hudsonicus)
• tufted-eared squirrels (Sciurus aberti)
• deer mice (Peromyscus maniculatus)

In montane forests in Colorado, Winternitz found an average of 0.6 breeding bluebirds/ha (Bureau of Land Management, no date). Territories averaged 0.43 hectares (Balda 1967) and 0.56 hectares (Szaro 1976) in two Arizona studies. Gopher snakes are common nestbox predators in central coastal California (Eichholz and Koenig 1992).

The distribution and abundance of this species is limited by nest site availability. For example, in northern Arizona, density increased from 9-21 breeding pairs per 100 acres to 65 pairs per 100 acres after nest boxes were added to the habitat (Brawn and Balda 1988).

Western bluebirds use a variety of calls to communicate. Communication begins as early as 14 days as nestlings call for food. Calls become more complex as western bluebirds grow older. There are a variety of calls that are used to determine the location of mates as well as to establish territorial boundaries. The "Kew" call and the "Che-check" call are used by mates to determine each other’s location. These calls are particularly important during breeding season. Additional calls are used to establish territorial boundaries. When building a nest, males produce a chatter call to establish their territories. If a foreign male invades another birds’ territory, the defending male will produce a squawk-like call. Calls are the common method of communication among western bluebirds and are used to establish boundaries as well as position.

Communication Channels: acoustic

We do not have information on lifespan/longevity for this species at this time.

Average lifespan

Status: wild: 73 months.

Western bluebirds are monogamous; they are also co-operative breeders ("helpers" or birds that are not the parents help to raise young). In some instances extra-pair copulation occurs (matings outside of the monogamous relationship). Helpers reduce the chance of extrapair copulations. They tend to fend off male intruders when the male mate is away from the nest. The females often use display signals to deter extrapair copulations (Dickinson et al., 2000). Females have been seen leaving their perch sites and attacking the breast of an invading male, as well as flattening themselves against a branch. The invading males typically flap their wings rapidly and call in a high-pitched tone (Dickinson et al., 2000). Most attempts at extrapair copulation fail because the female is not receptive. However, in a small percentage of cases extrapair copulations occur. If the intruding male is older than the female, then the female is more likely to mate with him (Dickinson, 2001).

Mating System: monogamous ; cooperative breeder

Both male and female western bluebirds can begin reproducing once they are a year old. Breeding occurs from May to July. Females typically lay one to two clutches (approximately 5 eggs per clutch (range 3 to 8)) during the breeding season. Copulation occurs from 10 days prior to egg laying through the last day of egg laying (Dickinson et al., 2000).

Incubation lasts from 12 to 18 days (Guinan et al., 2000). The nestlings fledge after 21 days, but they remain close. After two weeks, the young birds are fully independent (Guinan et al., 2000).

Breeding interval: Females typically lay one to two clutches per year

Breeding season: May to July

Range eggs per season: 3 to 8.

Average eggs per season: 5.

Range time to hatching: 12 to 18 days.

Average fledging age: 21 days.

Average time to independence: 2 weeks.

Average age at sexual or reproductive maturity (female): 1 years.

Average age at sexual or reproductive maturity (male): 1 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization

Average eggs per season: 4.

Female western bluebirds are responsible for incubating the eggs. Incubation lasts from 12 to 18 days (Guinan et al., 2000). During incubation, males guard the nest while the female searches for food. The female does not leave the nest for too long because the males do not incubate the eggs. Once the eggs hatch, both parents are responsible for taking care of the altricial young by cleaning the nest and providing food. Females also brood the nestlings. The chicks are able to leave the nest after 21 days, but they remain close. After two weeks, the young birds are fully independent (Guinan et al., 2000).

In addition to the mother and the father caring for their young, western bluebirds often have helpers at the nest (Kraaijeveld and Dickinson, 2001). These helpers are older offspring, who are non-breeders. The helpers may have been reproductively active at one point in time, but became helpers because their mate died or their nest failed. They increase their fitness by ensuring the survival of the fledglings who are related to them. For example, if a male bird does not reproduce, he is not passing on any of his genes so his fitness is zero. However, if a male bird helps at his parents nest, then some of his genes will be passed on because he is related to the fledglings. A helper increases his fitness by taking care of his siblings (Kraaijeveld and Dickinson, 2001).

Parental Investment: no parental involvement; altricial ; pre-hatching/birth (Protecting: Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Female); pre-independence (Provisioning: Male, Female)

Nesting may begin in March in some areas (usually in April-May in most areas), and may extend into July or August. Clutch size is 3-8 (typically 4-6). Most females produce or attempt two broods per year. Incubation lasts 13-14 days. Altricial nestlings are tended by both parents. Fledged young are tended by the male if the female re-nests.

Western bluebirds are not endangered; however, their habitat is threatened. Western bluebirds do not live in open areas; they live in the forest (Guinan et al., 2000). However, increases in logging have led to increases in the amount of open area in the forest, which has led to a decrease in the number of available nesting sites for western bluebirds. In addition to the loss of nesting sites, the suppression of forest fires has led to a decrease in edge habitat (Guinan et al., 2000). To prevent further declines in western bluebird populations, nest boxes have been set up throughout California to provide breeding sites (Dickinson, 2001). Western bluebirds are protected under the US Migratory Bird Treaty Act.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N4 - Apparently Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Comments: Local declines probably have been related to loss of nesting sites, which may result from the elimination of dead trees and branches, or from competition with house sparrows, starlings, or other cavity-nesting species.

Restoration Potential: See Mitchell (1988) for specifications for the construction and placement of nest boxes.

There are no known adverse affects of western bluebirds on humans.

Bluebirds are beautiful birds and people often put out nest boxes to attract them to their area.