Attracting Bluebirds

Attracting Bluebirds

~ MBA Attracting Eastern Bluebirds ~

(Permission for use granted by Edward Nied Jr.)~~ Getting Started ~~

Bluebirds are cavity nesting birds but lack the ablility to chisel out a nesting site on their own. In addition to natural cavities being in short supply, they are also usually taken by more aggressive birds such as European Starlings. To compensate, man-made nest boxes are used to help ensure bluebirds can find suitable nesting sites.

What kind of nesting box should I use? With a multitude  

of designs on the market, this may seem like a difficult question, so we will try to narrow down the choices. Bluebirds seem to prefer a cavity with an inside dimension of 4 to 5 inches with an adequate depth (floor to entrance hole) of 7 to 8 inches, so this will eliminate large and/or short boxes. Although not a preference for the bird, a 1 1/2″ entrance hole will cut down competition from other birds such as starlings. Also look for a design that easily opens to simplify monitoring and cleaning. A good nesting box will be made out of 3/4″ or thicker wood for proper insulation from the heat as well as the cold. I shudder every time I see someone selling birdhouses made out of 1/4″ plywood or tin roofs!

Not finding anything I liked initially, I combined and modified ideas from several designs over the years. Go to Eastern Bluebird House Plans to view my design with cutting and assembly instructions, if you’d like to build your own.

~~ When To Mount Nesting Boxes ~~

When is the best time to set out nesting boxes? To maximize your chances of attracting bluebirds, very early spring is your best bet. Here in Massachusetts, I like to have them up by early March. This will give most bluebirds a chance to claim boxes before the tree swallows arrive.

Actually, anytime is a good time to put up nesting boxes. Bluebirds will generally have more than one brood, so they may still be loooking for nesting sites in early and mid-summer. Recently I’ve noticed a number of bluebirds choosing to remain here during the winter months. I’ve always been at odds on deciding whether to take down nesting boxes or leave them up for the winter. I generally take most of them down for a new coat of linseed oil but leave at least one at each location. In some cases the houses were used by bluebirds through the winter months and some were taken over by mice. I even had a flying squirrel take up residence in one. I continue this practice just in case the birds need them. Sealing or covering the ventilation holes will help provide protection from the harsh winter weather.

~~ Nestbox Placement ~~

Whether you build your own or purchase, the next question is; where should you place them to best attract bluebirds? It’s been my experience that bluebirds are more easily attracted to large open areas such as pastures and hay fields, especially if there is a fence line. They seem especially fond of hunting insects from the vantage point of a fencepost or wire. This is not to say they won’t be attracted to a nesting box in a residential area, but between food requirements and the probable harrassment from house sparrows, you will most likely optimize your chances in large open areas. Most farms or people owning large tracts of open land will welcome the addition of bluebird houses (I’ve made many new friends this way) as long as you ask permission.

Placement: For monitoring and cleaning convenience, mount nesting boxes at eye level so they can be easily inspected without having to stand on something. This height is not only easier for us, the birds will also find it attractive. In addition, try to mount boxes so the entrance hole faces a small tree or bush, which will allow the young a safe landing place on their initial flight. You may also consider facing the entrance hole away from north or prevailing winds and harsh afternoon sunlight.

MOUNTING TIP: Nesting boxes are best mounted on electrical conduit or galvanized pipe, that raccoons, house cats and other predators cannot readily climb. These are available at most hardware stores, are inexpensive, and can simply be pounded into the ground anywhere you like. For a more secure mount, you can first drive a 5′ section of rebar (inexpensive rod for reinforcing concrete) 2.5′ to 3′ into the ground, then slide the electrical conduit over this rod. Several different predator guards can be attached to the conduit or pipe for added protection from predators.

Wooden fence posts are sometimes used but only for those areas with no predator problems. I used to mount mine by drilling two 1/8″ holes vertically   in the back of the house, then attach to fence posts using 2″ speed screws (drywall or deck screws). Many houses can be easily mounted this way using a cordless drill. Sometimes, if fenceposts are short, I will place the house on top of the post and use a 2″ X 18″ piece of wood, securing this to the back of the house and the fencepost. Existing wooden fence posts are certainly tempting to use for (our) convenience, but for the wellfare of nesting birds, I would now recommend the conduit or pipe installation.

Another question for house placement is; how far apart should the houses be mounted? I’ve varied this distance considerably over the years with no consistent conclusion. Some people mount boxes in pairs to minimize competition, so bluebirds and tree swallows, for example, can share the same territory without bickering over a single nesting site. This sometimes works, but I’ve had aggressive male bluebirds (an exception to the rule) that not only defended their own house but would not allow any other birds to nest in another house 30 feet away.

According to the North American Bluebird Society: “pairing boxes 5-15′ apart for tree swallows and bluebirds to cohabitate. One research study shows that tree swallows will not nest closer than 7′ together, so placing boxes under 7′ from each other will normally eliminate two pairs of tree swallows nesting together. Paired boxes or single boxes must be placed at least 300′ apart since bluebirds are very territorial. Placing them closer is shown to actually REDUCE the number of bluebirds nesting at that site because of territory requirements.”

~~ Monitoring A Bluebird Trail ~~

What is a bluebird trail? Almost any amount of nesting boxes mounted in a given area can be called a bluebird trail. A trail can consist of just a couple of boxes or hundreds of them, depending on your interest and preferences. Generally (if more than a couple) they are mounted in a line or along a fenceline where you will travel this “trail” many times through the course of the nesting season, checking activity. You could even set them out in a circlular fashion to enable you to start and end your walk where you park your vehicle.

OK, what is monitoring, anyway? In birding circles, people who maintain nest box trails generally like to keep records of any activity along the trail. As an example, if you know the date when the eggs in a certain house were laid, you will then have an idea of when to expect them to hatch and also when the nestlings will likely fledge (leave the nest). After some experience and by keeping track of nest building activity, you will eventually be able to tell what kind of birds are using a house by the material found in the box when the birds are not seen in the area. Keep a log by date and simply write down anything new that is found each time you visit. You may want to keep track of the type of material and when the nest was completed, date and number of eggs laid, when and how many hatch and the date and number of young that actually leave the nest.

How often should a trail be monitored? Plan to monitor your bluebird trail as often as you can. Usually a weekly visit is enough to gather information on when nests are built, eggs are laid/hatched and dates when young leave the nest. Not only will the birds need your assistance at times, but if you take some time to just observe the birds along your trail, you will be rewarded with endless hours of entertainment. With that discovery, you will probably find yourself visiting more frequently.

~~ Season Expectations ~~

Anything can happen during the course of monitoring your bluebird trail from finding flying squirrels/mice inhabiting a box or learning that a racoon is making nightly egg raids. For now, I will attempt to discribe activities usually found at a typical bluebird nesting site which will give you at least some insight as to what to expect.

If a male bluebird arrives at your site alone, he will generally stay in the area calling for a mate. Sometimes they arrive already   paired and may even have some of their previous offspring in their company. In either case, it seems to me that the female has the final say in choosing a nesting box. If the birds are satisfied with the site, the female will begin bringing nesting material into the house. The male will sometimes help with this chore and at times will bring food for the female who is busy constructing the nest. Once the nest is completed, you will see less activity at the house. Soon the female will begin to lay her eggs, one a day, usually in the morning. The birds will remain in the area but will minimize activity at the nesting box. After she has laid a clutch of eggs (normally three to five), the female will now spend most of her time incubating them. Occasionally she will leave the house to stretch, get a drink or take food from her mate. Meanwhile the male is busy defending his territory and foraging. He will appear at the house every 20 minutes or so with food for the female.

It takes approximately 12 to 14 days for the eggs to hatch. The young will remain in the nest for another 16 to 21 days, during which time both adults will be busy fetching food for them. This is the best time to watch your birds, as this phase of the nesting season brings the most activity at the box.

When the young leave the nest to become fledglings, the box will become inactive again while they learn to fly and gather food on their own, with the adults watching over them. This is usually when I will remove the old nest from the box. The adults may return and start the process all over again, with the juveniles sometimes helping to feed the second brood. On occasion, bluebirds will have as many as three broods during a season, although two is the norm.

~~ What You Can Do To Help ~~

At times, the adult bluebirds can use an extra hand, which is another reason to monitor your trail regularly through the season. I remember my first year, eggs kept disappearing from one of the houses. I reasoned that a raccoon was stealing them at night. The problem was solved by modifying the house: I nailed another 3/4″ piece of wood with a 1 1/2″ hole to the front (predator guard), so the thief could not reach the eggs. Although I’ve used this method as a “quick fix”, the North American Bluebird Society (NABS) has recently decided that these predator guards are not 100% effective and so suggest using pipe or electrical conduit poles with an application of silicone spray. A predator cone, baffle or PVC pipe guard on the pole is also recommended.

Another problem bluebirds face during the warmer summer months are blowfly larvae. These are small football-shaped   creatures, about the size of a small pea. The adult flies lay eggs in the nesting material. After hatching, they spend their larval stage in the nest, and live by sucking blood from the bluebird nestlings, undetected by the adult birds. This problem is easily dealt with by simply lifting up the nest and removing them. I usually go a step further and eradicate them. (Yes, throw them on the ground and stomp on them!) There may be times when the nest is so compacted from the weight of the nestlings, and so infested with larvae, that it must be removed. Gingerly take the nestlings and the nest from the house. Then fashion a new nest using the finest grass you can find, or pine needles if they are at hand, and replace the nestlings. The two young nestlings in photo at left where photographed on an old tee shirt while a new nest was being made for them. With a severly infested nest it is doubtful the young birds would survive without this intervention. Recent studies indicate that blowfly larvae themselves will not kill the young birds, but may contribute to a weakened condition where heat or other problems could cause nestling fatalities.

There is no truth in the old wives’ tale that adult birds will abandon their offspring if the young are touched by humans. Adult birds may chatter at you, and carry on a bit, but 10 minutes after you leave the nesting area life will return to normal, only healthier. Other birds, such as tree swallows (and on rare occasions, bluebirds) may dive-bomb you when you are near the nest. This can be a little unnerving if they brush your hat or hair. The trick here is not to think about Alfred Hitchcock’s movie, “The Birds,” but to carry on with the task at hand.

Speaking of other birds…tree swallows, wrens, tufted titmice, chickadees and house sparrows may be found using nesting boxes. All but the house sparrow are native species and are welcomed occupants along most bluebird trails. If fact, you will especially appreciate tree swallows nesting in your area, as they consume thousands, maybe millions, of flying insects.

House sparrows are a non-native species which are not protected by law like our native songbirds, and are generally regarded as a nuisance. Once you have gained some experience with sparrows, you will discover why they should NOT be allowed to nest in your bluebird trail.


If you are making a serious attempt to attract cavity nesting birds such as bluebirds, you will eventually want to learn how to deal with house sparrows. In the following paragraphs, I will discuss some of my own experiences, which I hope will help you in the future.

In my early stages of bluebirding, I attended a program at a local Audubon sanctuary. Although I cannot recall the speaker’s name, I do remember his utter disgust upon mentioning house sparrows found along a bluebird trail. He told of how he not only removes their nests and destroys their eggs, but if he can get his hands on one of the adult sparrows found on the nest, he quickly dispatches them by breaking their necks! At the time, I thought this action seemed a little harsh and perhaps the speaker was a couple eggs short of a full clutch. After all, these were cute little birds too. If you have similar thoughts and are new to attracting cavity nesting birds…READ ON! (please)

For whatever reason, I experienced no problems with sparrows during my first two seasons of bluebirding. However, during my third year, my attitude towards these “cute little birds” quickly changed and I realized that the speaker heard at the Audubon program had been dealing with a full deck after all!

My first attempts to discourage sparrows from nesting on my trail involved removing their nesting material. I understood that sparrows were undesireable tennants and figured this would be a humane way of dealing with them. Sparrows just wont take a hint and could very well be the most persistant critters on this planet. Soon tiring of this never ending chore, I allowed them to complete their nest. When their clutch was complete, I then removed and destroyed the eggs. The following day at this location, I discovered sparrows in a nearby nesting box that had been occupied by bluebirds. Closer inspection found a few broken bluebird eggs on the ground in front of the house and two broken eggs still in the nest. At the time, I thought this to be coincidental, but this same senario occurred at a different location the following week. I couldnt help thinking the sparrows were wreaking this havoc as some kind of revenge for their own loss, or so it seemed.

That same season was the first time we had bluebirds nesting at one of two boxes in our yard, with sparrows moving into the other. This time I did not want to disturb the sparrows, fearing retaliation to the bluebirds. We noticed the sparrows would harrass the bluebirds on occassion but the male bluebird seemed capable of defending his territory. Returning home from work one day when the bluebird nestlings were about a week old, I saw the female sparrow exiting the bluebird box. From what I saw, it appeared the male sparrow kept the adult bluebirds busy while the female sparrow entered their nest and did the dirty work. To my dismay, I found all five bluebird nestlings dead! This was my turning point, the last straw! I was furious because there seemed to be no logical explanation as these sparrows already had their own (undisturbed)nest. I waited until later that evening and could feel the female sparrow when I placed my hand on top of their nest. Although I hate to admit it, I can tell you now that I experienced at least some satisfaction after breaking her neck and destroying the eggs. I can remember becoming frustrated by not being able to capture this particular male house sparrow, but if this was the same bird that returned the following year, then sentencing was carried out.

Over the years Ive seen first hand what sparrows can do. On more than one occasion I found where these nasty little birds had killed adult bluebirds and tree swallows while they sat on their eggs and began building a nest right on top of them! As mentioned above, Ive seen sparrows work together, whether in pairs or in larger groups later in the season. They will work relentlessly to take over or destroy other birds nesting sites for no apparent reason.

To help better explain, here is a question I ran across from a person new to attracting cavity nesting birds and my reply:

QUESTION: “I was disappointed to read a bluebirding article that encouraged trapping and destroying house sparrows. As a new birder, I feel it is our duty to help conserve and manage all wildlife, and it is hypocritical to destroy those species which we do not like. Their place in nature is also part of the food chain and let us not forget that nature is very, very cruel!”

REPLY: “I felt the same as you when I first began bluebirding about 10 years ago. I have a website (referring to this page) where I have recounted my experiences and have attempted to deal with this issue in a way that I hope will help beginners understand.”

“In your own words about sparrows having a place in the food chain… consider this…I don’t hold any “grudges” against hawks, crows, bluejays, etc., if they happen to take one one of “my” bluebirds. This is nature in action and part of the food chain as you state. House sparrows on the other hand, do not kill for food and their actions are not consistant to nature’s food chain. I can’t say for sure, but it appears sparrows kill for no other reason than to continue their quest to take over the (bird) world.”

Keep in mind that sparrows are usually found in city and urban areas and have the ability to build nests almost anywhere. Under roof eaves, in street light fixtures/poles, building ledges/crevices, awnings, you name it. They are not restricted to nesting boxes like some of our native species, such as bluebirds and tree swallows!

I maintain a couple of small bluebird trails around town, but two nestboxes are located in our yard in a somewhat residential neighborhood. Because this location prohibits the use of a firearm, I use a Gilbertson Sparrow Trap to deal with house sparrow problems. It’s a fairly simple affair made from a small piece of wood, a 4″ section of metal measuring tape, and two pieces of cleverly bent coat hanger. The trap is screwed to the inside of the nestbox, just under the entrance hole. If set properly, it will trip when the bird enters the house and hits the coat hanger wire. The section of measuring tape then snaps up to cover the hole, thus trapping the bird. This type of trap is non-discriminatory and must be used under supervision so desireable birds are not caught.

Another good design is the Huber Sparrow Trap. This link for Joe Huber’s web page will provide detailed instructions for making one.

For more information on sparrows, go to the House Sparrow Page by Steve Eno.

(Link back to home page here)