Bluebird Trails Project

One of the conservation projects of Sierra Foothills Audubon Society is our Bluebird Trails nest box monitoring project. Over the years, trails of human made nest boxes have been created throughout Placer and Nevada Counties and volunteer monitors keep track of breeding activity during the spring and summer months.

We currently have three active trails in Placer County and 20 trails in Nevada County. Trails consist of between six and 42 nest boxes mounted along trails in areas supporting populations of Western Bluebirds.

In addition to these trails established by SFAS, we have individual property owners who monitor boxes on their own property and participate in our data gathering and reporting activities. We actively seek out areas for additional trails, especially large land holdings such as ranches, farms, or other rural properties where the habitat is just what the bluebirds need – large areas of short grass bordered by stands of trees and having water available nearby. Please contact us if you have such a property and would like to participate in this citizen science project.  

A little review about bluebird population trends over the past 75 years will help explain why SFAS builds nest boxes and monitors them. In the 1940’s the Western Bluebird population began to decline in Washington, Oregon, and California. There were many changes taking place at this time, notably changes in agricultural practices, use of pesticides, development of large suburban areas, and increased competition from House Sparrows (invasive species, boo-hiss). Concerned individuals responded by forming local bird clubs and establishing bluebird nest box trails. Since then, the Western Bluebird has made a strong comeback, but the destruction of bluebird habitat for urban development continues. Therefore, efforts by organizations like Audubon, the North American Bluebird Society, and the California Bluebird Recovery Program continue their work to support the breeding success of these dazzling blue flying gems.

ImageImage California Bluebird Recovery Program. Collects data throughout California on breeding success of many different cavity dwelling birds. SFAS sends local data to CBRP who analyzes data for population trends and forwards the data to North American Bluebird Society. NABS has fabulous fact sheets to help get you started monitoring bluebirds; check out their website for information such as Getting Started with Bluebirds .

The websites above are wonderful places to explore, and you can see photos of typical nests along with eggs, photos of the birds who might also be utilizing your nest box, and you should especially take note of the House Sparrow photos so you can recognize the birds and their nest so you can be sure to keep them from using your nest box. There also downloadable plans for bluebird nest boxes.

Recommended Reading: BLUEBIRD BOOK: The Complete Guide to Attracting Bluebirds by Donald & Lillian Stokes

If you have any questions about getting started with bluebird monitoring, you should contact Kate Brennan,  Bluebird Trails Project Coordinator:


Installing and monitoring Western Bluebird nest boxes is a form a CITIZEN SCIENCE that is easy to get involved in. If you have property, simply build or obtain a nest box designed for bluebirds, install that box on your property and then in the spring follow our guidelines for monitoring (see below). You can choose to report the data you collect to our Bluebird Project Coordinator, or you can report directly to the CA Bluebird Recovery Program (CBRP). Links are given below.


In order to be successful in providing a nest box for bluebirds, you should only install a box in an area where bluebirds are frequently seen. You generally cannot attract bluebirds to your property by installing a box. Bluebirds are looking for sites that have wide open expanses with short grass (like pastures) that are bordered by woods or at least scattered trees and brush. They need the grassland area for hunting for bugs to feed their young. They need trees in the area for perches from which to hunt for the bugs. A bluebird pair feeding a nest of 5 young will have to provide 300-500 insects per day for food – that’s a lot of bugs! They also need a nearby source of water, which can be a bird bath or a small pond or stream; but if there is no water available, they probably will not nest there.

So, let’s say you have the perfect location for bluebirds – you see them regularly on your property and you have grassland and a water source over the fence. Perfect. Installing your bluebird box on a metal pole will help ensure that predators such as raccoons will not be ransacking your nest box. The opening to the nest box should face away from direct afternoon sun in the summer – so east, north, or northeast. If possible, afternoon shade may make a difference when the temps reach 100 degrees.  And the box should be within 50-100 feet of a small tree or shrub, so those fledgling bluebirds have something to land in on their first flight, something to keep them off the ground where predators lurk. [It is worth mentioning here that if you have outdoor cats, please do not install nest boxes on your property – you could be creating a death trap for baby birds.] The box should be installed at a height that will be convenient for you (or your children) to look inside and easily monitor activity. However, they should not be any lower than 4’ from the ground.

Sometime in January and early February, male bluebirds will begin checking around for appropriate nest sites. If they favor your nest box, they may place a “claiming” stick in the bottom of the box. This seems to tell other males that someone is already interested in that box. When the females arrive on the scene and birds form breeding pairs, the male will take the female around to the various boxes he has “claimed” and she will make the final decision on where to begin building a nest. If you see bluebirds carrying grass in their beaks, you know they have selected a nest site somewhere nearby and are beginning to build their nest.

At this point, it is imperative that you monitor your box weekly to ensure that it is indeed a bluebird taking up residence there. If your nest box has the appropriate opening of 1-1/2”, not only bluebirds can use it, but others may also find it attractive as a nest. These other songbirds should be allowed to use the box, and you can monitor their activity just as you do the bluebirds. These include House Wren, White-breasted Nuthatch, Ash-throated Flycatcher, Tree Swallow, and Oak Titmouse. HOWEVER, the House Sparrow, or English Sparrow, is an INVASIVE species and is a very aggressive bird who will destroy bluebird eggs, and even fight and sometimes kill adult bluebirds. You must ensure that you are NOT providing a home for the House Sparrow. Familiarize yourself with what the male and female look like, what their nest looks like (it is VERY distinctive) and if you see them building a nest, you should destroy it – over and over again, if necessary. Federal law prohibits the destruction of any native migratory songbird nests, but the House Sparrow, as an invasive species, is not a protected species. Please be sure to destroy the nests of House Sparrows.

Once your bluebird nest is completed, the male and female may both take a bit of a vacation and might not be seen for a week or two. However, when they return, the egg laying process will begin and the female will lay one egg per day until her clutch is complete. A typical clutch of eggs for bluebirds is five, but they may lay from 4 to 7 eggs in a nest. This is when monitoring becomes addictive. You should plan to monitor your nest box at least once per week until the babies have fledged (flown the nest). Incubation by the female begins when the last egg is laid and will continue for about 13-14 days. Note the date of the last egg; then you can count and know when to expect the first babies to appear in the nest. After hatching, the chicks will remain in the nest for 17-18 days getting fat, building up muscle in their wings, and learning how to fly up and down inside the nest box. Monitoring (opening up the nest box door) should be curtailed about 14 days after hatch so you avoid opening up the box too close to fledging and possibly causing them to fly out before they are totally ready.

If you begin observing the box obsessively around the 15th day after hatch like I do, you may see the babies flying up into their entrance hole, checking out the world outside, then dropping down for a sibling to fly up into the hole and do the same. This is very entertaining, but can become slightly addictive, with the monitor expecting at every baby face appearance, that someone is about to fledge. Get your camera set up and you may get some great baby pictures.

Once they fledge, they do not return to the inside of the nest box. They may light on top of the box to let parents know they are hungry, but they generally don’t go inside. So, it is appropriate at this time to clean out the nest box, after you’re certain all the babies are gone, and being careful to remove all the nesting material from the area. Cleaning out the nest box will encourage that pair or a new pair to take up residence and begin another brood. 

During a typical breeding season, March through August, with results coming in from monitors of about 190 nest boxes, we see between 600 to 650 Western Bluebirds fledge, along with another 150 to 200 fledglings of other species, including Tree Swallow, Violet-green Swallow, Ash-throated Flycatcher, Oak Titmouse, White-breasted Nuthatch, and House Wren.