Western Bluebirds Breeding Time is Coming

By Eileen Richardson

In open parklands of the American West, brilliant blue-and-rust Western Bluebirds sit on low perches and swoop lightly to the ground to catch insects. Deep blue, rusty, and white, males are considerably brighter than the gray-brown, blue-tinged females. Male Western Bluebirds are shiny blue above with rust-orange extending from a vest on the breast onto the upper back. Females are gray-buff with a pale orange wash on the breast and blue tints to the wings and tail. The throat is blue in males and gray-buff in females, and the lower belly is whitish.

Western Bluebirds are small thrushes that usually perch upright. They are stocky with thin, straight bills and fairly short tails. This small thrush nests in holes in trees or nest boxes and often gathers in small flocks to feed on insects or berries, giving their quiet, chortling calls.

Behavior

These birds are highly social, and usually feed in flocks during the non-breeding season. They hunt for terrestrial insects by dropping to the ground from a low perch. Western Bluebirds also frequently feed on berries in trees. I have seen them eating the juniper berries near my house. Western Bluebirds rely on trees both for nesting cavities and hunting perches, and also perch on fences and utility lines.
Habitat. Look for Western Bluebirds in open woodland, both coniferous and deciduous. They also live in backyards, burned areas, and farmland, from sea level far up into the mountains.

Similar Species

All three bluebird species can be found in New Mexico. Mountain Bluebird males are a lighter sky-blue above and below. Females are grayer overall, and usually show less rust on the breast than Western Bluebird. Eastern Bluebirds have only a small range overlap with Western Bluebird. In the eastern species, the throat is rusty-orange (males) or white (females), the belly is crisp white, and the back in males is entirely blue. Male Lazuli Buntings are considerably smaller than Western Bluebirds, with thick, seed-eating bills and prominent white wing bars. Though blue, California and Woodlouse’s scrub jays, and Steller’s Jay are much larger, noisier birds with longer tails, heavier bills, and without any rusty coloration.

Pairing may occur as early as late January or as late as mid-April. And can begin very early when winters are mild. February to Mid-March: Bluebirds start establishing breeding territory and checking out nesting sites. Male shows nest sites to female (may bring along a little nesting material); female makes final selection (good sign but no guarantee if both go in the cavity at the same time.) Late arrivals, or previously unpaired birds may nest as late as July or even August. If there are not very many nesting sites around, the search may take a long time. It's never too late to put up a nest box, as they may be used for a subsequent nesting for roosting, and are also often checked out in the fall or during a mild winter by birds that may return the following spring.

It is Extremely rare to make an open cup nest ( sometimes people confuse an open cup Robin's nest with a Bluebird nest due to blue eggs). A few  nests have been reported in building crevices, mud swallow nests, purple martin boxes, and a metal clothes poles. Females do not breed until the year after they are born.

Nesting Behavior is “socially monogamous," although if a mate is lost they will readily pair up with another available mate. Cooperative breeding (e.g., one male with two females and even 2 females in same cavity, or one female nesting with more than one male) is rarely reported. Sometimes fledglings from the previous brood will help tend to the subsequent brood (called "helping Adult males or adult pairs may also help. Females will "beg" from males (possibly to test their foraging skills). Males and females may fight with each other during nesting season.

If you want to see these beauties in your yard you can purchase or build a nest box. Build or purchase a nest box designed specifically for bluebirds. WEBLs may need a larger entrance hole than EABLs. WEBL and MOBL ranges overlap in some areas, and MOBL's need a 1 9/16" hole. It has been observed that some of the Western population cannot or will not enter 1.5" holes. My recommendation would be for bluebird observers to offer the largest hole size possible that will still exclude Starlings.

Bluebird boxes are made of PVC or unpainted, untreated 3/4" - 1" wood, have an overhanging slanted roof (2-5", with a shallow saw kerf (groove) to keep rain from soaking into box), no perch, ventilation, drainage holes, deep enough so predators can't reach in and get to the eggs, and a door that opens for cleaning and monitoring (if rough wood is not used, add kerfs to inside of door to enable fledglings to climb out). MAY prefer boxes mounted on wooden posts vs. steel but be careful to not allow the pole to be a way predators can get to nests.

Because we have had nest boxes for the last 4 years in my yard and add one a year, we have seen generations of the Western Bluebirds breeding, nesting and thriving all year round! So much fun to watch.