1 A Male WesternBluebirdPhoto by DessiSieburth

A male Western Bluebird (Photo by Dessi Sieburth)

By Dessi Sieburth

Western Bluebirds (Sialia mexicana) are small thrushes which can be found year-round in Los Angeles County. Their primary habitat is open grasslands or parks, and their diet includes berries and insects. Western Bluebirds are cavity-nesters, which means that they make their nests inside cavities in hollow dead branches or trunks of trees. Bluebirds can not make their own cavities, as their bills are not strong enough to chisel out the wood. Instead, they rely on finding cavities that have already been made by woodpeckers. Woodpeckers have very strong bills and are excellent cavity makers. The woodpeckers use the cavities they make for nesting, and when they are done nesting, the cavity can be used by another cavity nester, such as a Western Bluebird. In fact, over 80 species of North American birds nest in tree cavities, highlighting the importance of dead trees and branches for birds. Unfortunately, we often cut down dead trees for safety or for aesthetic reasons, which destroys potential nesting sites for many species, including our Western Bluebirds.

2 A female WesternBluebird feeds her young Photo by DessiSieburth

A female Western Bluebird feeds her young (Photo by Dessi Sieburth)

In the early 20th century, Western Bluebirds were reported to be common summer residents from the foothills to the mountains up to 10,000 feet in Los Angeles County. However, Western Bluebirds started declining in the 20th century due to habitat loss and the introduction of European Starlings and House Sparrows. The starlings and House Sparrows, which were introduced from Europe, are also cavity nesters and compete with bluebirds for nesting habitat. Both species have been known to kill both the adult and young bluebirds.

3 June July 2017 Map from ebird.org

The Western Bluebird is now a common breeder in the lowlands and mountains of Los Angeles County (June and July 2017 map from ebird.org)

In recent decades, however, the Western Bluebird has made a comeback and is now a widespread and a common year-round visitor in Los Angeles, thanks to the Southern California Bluebird Club. The Southern California Bluebird Club was founded in 1984 by Dick Purvis and three other bluebird enthusiasts to provide nesting sites for bluebirds by hanging bluebird nest boxes in trees. Bluebird nest boxes are installed on tree branches about 10 feet high. They are made of wood, and their entrance holes are small enough so that starlings can not enter. Bluebird nest boxes are mainly responsible for the increase in the Western Bluebird population in Southern California. The California Bluebird Recovery Project (http://www.cbrp.org/) keeps records of all the bluebirds raised in nest boxes throughout California, and last year, 11969 Western Bluebirds were raised.

4 Bluebird nestbox cycle monitoring

This image shows the bluebird nest box cycle (by Dessi Sieburth)

In 2013, my friend Norm Vargas and I decided to build and hang up bluebird nest boxes in Los Angeles County. First, I hung five boxes at an Equestrian Center in Sylmar. In 2014, I expanded my nest box project by installing more boxes at a local cemetery and around my neighborhood. I ended up with 22 nest boxes. During the breeding season, which goes from April to August, I monitor the boxes once a week by taking each one down and looking inside to count the eggs and young. If there are any House Sparrow nests I remove them. I found it amazing to see a bluebird pair build their nest, lay the eggs, and feed the young. Each week, I could see the young bluebirds inside the box gradually grow and mature. It takes 21 days for the young to fledge. Bluebirds are socially monogamous, but the nests can sometimes have more than one male parent. Several times, I witnessed three bluebirds (usually 2 males and a female) all working together to raise a brood. The second male was likely from a previous brood. Once, when I opened a box to check it, a White-breasted Nuthatch, another cavity nester, was nesting inside the box. The nuthatch pair ended up raising four nuthatch fledglings in the bluebird nest box.

5 White breasted Nuthatch

This White-breasted Nuthatch was using one of my bluebird nest boxes (Photo by Dessi Sieburth)

I have been monitoring the same bluebird nest boxes for five years, and I now have put up 22 boxes in three different locations. When I started in 2013, five bluebird fledglings were raised, and this year, 120 bluebird fledglings were raised in my boxes, with an increase in fledglings each year. The bluebird nest box chart shows my data from 2014 to 2017.

6 Western Bluebird nest boxes monitored by Dessi 2014to2017 Graph2

Western Bluebird nest boxes monitored by Dessi Sieburth in Los Angeles County

There are simple things we can do to help the Western Bluebirds in Los Angeles. First, we can help them by not using pesticides. Birds may ingest and swallow pesticides or bathe in poisoned water. Instead of using pesticides, you can plant native plants such as yarrows, California Buckeye, manzanitas, milkweed, wild lilac, and coyote bush to attract beneficial insects and keep your garden in a balance. Second, outdoor cats kill millions of birds each year, so keeping them inside is good for all birds, including bluebirds. Finally, if you have a dead tree or tree branch in your yard, consider not cutting it down entirely. Even leaving five feet of a stump or a few feet of a branch can be enough to provide nesting habitat for cavity nesters. Of course, it is important to consult an arborist about safety when leaving parts of a dead tree. To learn more about the management of dead trees please go to: http://cavityconservation.com/saving-dead-trees/. If you like to learn more how you can help birds go to my website: http://protectingourbirds.my-free.website/.

7 FledglingWesternBluebird

A fledgling Western Bluebird. This fledgling is likely a male due to the deep blue tones in the tail and wings (Photo by Beatrix Schwarz)

Thanks to Norm Vargas for helping me with my bluebird nest box project, Gillian Martin for mentoring me on cavity conservation, Los Angeles Audubon Society for supporting my conservation efforts, and Pasadena Audubon Society for providing a grant to build the nest boxes.

For more information on bluebird nest boxes please visit:

Allen, L.W. , K. L. Garrett, and M.C. Wimer. Los Angeles County Breeding Bird Atlas. Los Angeles, California: Los Angeles Audubon Society, 1994. Print.
Olson, M. A., hole lotta love for the Western bluebird. latimes.com,16. July 2018. Web.