BIRD COLUMN FOR June 27, 2004
By Benjamin P. Burtt
Topic: How to Attract Bluebirds
Making a bluebird nest box, where to place it, protecting the nest box from house sparrows, starlings, tree swallows and raccoons and regular maintenance.
The eastern blue bird has a special appeal to most of us. It has stirred poets and ordinary folk for nearly 400 years since the first one was spotted by the early settlers of the Plymouth Colony. They reported it as a friendly, cheerful songster. To them, it resembled the familiar European robin, their "Robin Redbreast". This new bird had a reddish breast and a blue back and they called it "The Blue Robin".
CAPTION: The eastern bluebird is shown here with the male in the center with its blue back and rusty breast. The female at the top is brown with a bit of blue in the tail and wings. The immature also is brown, but it has a speckled breast with some blue on the wing. This painting by Roger Tory Peterson is from his field guide "Birds of Eastern and Central North America", Fifth Edition and is used Courtesy of the Houghton Mifflin Co.
The bluebird has two habits that have strongly affected the ups and downs of its population.
1. It must find a cavity for its nest since it can not make one.
2. It needs to live in open area where the grass is short and there are scattered trees. There it forages for its insect food on the ground . Generally, it spots the insects while perched in a nearby tree or shrub and then drops down to the ground to seize its prey.
Bluebirds before Europeans arrived
Before the Europeans arrived on the east coast, the country was largely forested. Cavities for nesting were available as older trees rotted. and left hollows. Woodpeckers dig their nesting cavities only in dead trees so where there were dead trees, there were old woodpecker holes left from earlier nestings.. These could be used by bluebirds as the woodpecker almost always prepares a new nesting cavity each year.. Forest fires did produce dead trees so that helped the woodpeckers and then the bluebird.
Bluebirds only existed where there were grasslands or barren places that occurred naturally. Some suitable habitat was produced by the Native Americans when they used fire to promote hunting and berry gathering. There were not very many holes available and due to the forests, there was little open land. So the bluebird was probablly not very abundant.
Bluebirds after the Settlers began to Farm
As the Europeans cleared the trees for farming, much open land was created and the bluebird population grew. For about 200 years it was a familiar and welcome door-yard bird in the towns, villages and on the farms of the eastern United States. Part of the appeal was the birds beautiful colors of blue and rust, as well as its gentle habits and tendency to live near humans.
The heyday of the bluebird
Many new cavities for nesting became available. Apple orchards were common and the older trees produced many holes suitable for nests. Wooden fence posts rotted to produce hollows. Some people began to put up nesting boxes in the middle to late 1800s and it seemed as if we would always have an abundance of bluebirds. There certainly were more bluebirds than ever before..
The Decline of the BluebirdThen humans stepped in and inadvertently began to spoil things for bluebirds. In 1851, the house sparrow was brought to this country and in 1890 the starling was imported. Both species use hollows and woodpecker holes for nesting, and will take over any nesting box they can get into. Many bluebird-nesting sites were lost through these aggressive species, particularly in towns and villages. The bluebird population began to decline.
Changes in farming practices further decreased the number of cavities available for the bluebird. While old fruit trees in orchards contained hollows, modern orchards consist of young, well-pruned trees with few hollows. Hollows in old wooden fence posts were often used, but when metal posts replaced them another group of nesting sites disappeared.
By 1930, the population was way down. Bluebirds retreated to the countryside and no longer were found in villages and towns. Fewer cavities were available. Dead trees were removed near homes.
Helping the Bluebird
About this time some concerned people began to promote the idea of setting out bluebird nest boxes and Lawrence Zeleny started the North American Bluebird Society. .
While the population of this bird in the eastern United States has increased markedly since the 1930s, you and I will not see bluebirds, unless we put up nest boxes in suitable habitat.
In New York State along the 420 miles of Route 20 from the Massachusetts border on the east to Pennsylvania on the west, 1700 bluebird nest boxes have been installed by many different individuals. who also provide maintenance and care. That is, they clean out the nesting material when the young have fledged and make certain the boxes are in good repair.
Another such trail runs along Route 11 from Champlain in the north to south of Binghamton near the Pennsylvania border. The trail has some 34 people helping keep the 500 boxes available along 325 miles of Route 11.
Other individuals operate their own "bluebird trail" with perhaps 10 or 20 boxes along country roads close to home. One of the largest in Central New York is managed by John Rogers of Brewerton who has 205 pairs of boxes along country roads for a distance of about 250 miles. So far this season, 85 pairs have produced some 220 fledglings.
Then there are many people like myself who put out a few boxes on their own land just so they can enjoy bluebirds close by. It is for you that this document has been written.
Making a Nest Box for Bluebirds
You can purchase bluebird nest boxes already made at many stores that specialize in materials for attracting birds. However, many people like to make their own. The nesting box illustrated below has been carefully designed to meet the requirements of bluebirds. It will last for years when maintained properly.
The dimensions given in the drawing are for boards that are 3/4-inch thick (this is called "1-inch wood," which was its thickness before it was planed down to 3/4 inch). Cut the pieces as shown in the diagram.
Note that the entrance should be circular and exactly 1-1/2 inches in diameter. Bluebirds can use a larger entrance, but so can starlings.
The inside of the front board should be roughened to aid the young birds in getting out. A series of horizontal saw cuts or a number of small holes 1/8-inch deep will do. Other alternatives are to tack on tiny cleats or a piece of half-inch mesh hardware cloth.
Boxes made with iron nails will last several years. But these nails eventually rust and become loose. Brass or stainless steel screws are preferred. Even nails: made of aluminum or those that are galvanized will be better than regular iron nails. You may want to apply a good exterior glue in the joints before nailing. This will strengthen the box further and help seal the joints against the rain and ice.
Some types of wood have a tendency to split when nailed close to the edge or close to the end of a board. To avoid this, it's helpful to drill pilot holes in the board through which you are nailing. Pilot holes will help steer the nails straight into the adjacent board. These holes should be, slightly smaller than the diameter of the nails you are using. If you are using wood that is actually 3/4 inch thick, six penny nails are the proper size to use.
To allow the front to pivot open, fasten it to each side with one nail or one screw about 1-1/2 inches down from the top. Make certain the nails or screws are positioned on both sides exactly the same distance from the top so the front will pivot properly and not bind when opened. Also make certain the front board has about 1/8-inch clearance at the top to keep it from binding against the roof when the box is opened. This clearance space also provides needed ventilation.
The square floorboard should be installed next. Place it with the grain of the wood running from side to side. This will insure that the screw used to hold the front will be seated firmly and not wear out the screw hole as it is taken in and out. Insert the floorboard and recess it slightly so the sides and front extend below the bottom of the box. The dotted lines on the diagram of the front board: shows the position of the floor. Then nail the back and finally the roof in place.
If possible, the back edge of the roof should be beveled to fit snugly against the back board. Beveled or not, the joint where the roof joins the back should be caulked along with the joints between the sides and back board. A piece of scrap wood also may be fastened to the backboard just above the roof to provide protection from the rain.
If the box will be located on your own land and is unlikely to be disturbed by humans, you can keep the front closed with an easy opening arrangement such as an L screw or a bent nail through a slot in the front and into the floor (see drawing).
On public lands, the screw and washer method is a must. A pilot hole is drilled through the bottom edge of the front board and into the floor of the box for a single screw, which holds the front, shut. A washer should be placed under the head of the screw. Only this screw has to be removed to open the box. The pilot hole should be slightly larger than the shank of the screw. It is best drilled in two steps, using a smaller drill bit first. The smaller hole through the front board should continue into the floorboard. This will guide the screw into the bottom piece and prevent its splitting.
In either case, the fastener must be attached so it requires some dexterity and force to open the box. Otherwise you may find a raccoon will discover how to open and rob it.
Drainage and Ventilation
Since rain may enter through the entrance or through cracks, drainage must be provided. To help, cut about 3/8 inches from each of the corners of the floor before you nail it into place. The floor is recessed slightly for better protection from the rain. The roof is wider than the box and extends well over the entrance hole.
If the box becomes too hot, the eggs may be spoiled or young birds may die. The 1/8-inch clearance at the top of the front board lets hot air out. Additionally, a few ¼-inch holes can be bored high on the sides of the box. If this is done, they should be sloped upward towards the inside of the box to keep the rain out.
Painting the Wood
A weathered, unpainted nesting box is the nearest thing to a natural cavity. You may wish to protect the wood from rotting, especially if the box is not made of decay-resistant cedar, redwood or Cyprus. Exterior grade plywood is excellent, especially for the roof. If paint is used, you should select a light shade of brown, green or gray exterior latex paint and paint only the outside of the nesting box. Subdued colors are less likely to be conspicuous and invite vandalism. They also are less prone to absorbing the heat of the sun and may be noticed less by a roaming predator.
One of the simplest and best ways to protect the wood is to paint it with raw linseed oil (containing no - additives). Treat the box inside and out and repeat the treatment until the wood is well saturated. Pine boxes treated in this way have lasted 20 years. Raw linseed oil reacts slowly with the oxygen in the air to form a tough, hard material that does not vaporize or harm the birds in any way. However, it may take a month to set up, after which there will be no odor.
Do not use any wood preservative on the inside of a nesting box where occupants may come in contact with it. Most of the other preservatives are highly toxic and little is known about their possible long-term effects. If you wish to give a mottled natural appearance to the box, you can add some stain or a bit of green, oil base paint (containing no lead) to the raw linseed oil applied to the outside of the box. If it is applied without stirring, it will give a mottled natural appearance.
Best results, will be obtained through careful selection of the habitat in which the nesting box is mounted.
Bluebirds prefer open, sunny locations where the box may be seen while they are foraging or perching. Nearby perches are an important element for successful nesting of bluebirds and should not be overlooked when planning nesting box locations. Best of all is an open area with scattered trees, but power lines and fences are adequate substitutes if there are no trees for perches. The box should face an open area with a tree, a large shrub or fence from 25 to 100 feet in front of it. The young birds usually will reach this on their first flight and have a better chance of surviving during the first crucial hours out of the nest.
Bluebirds will not nest in cities, large towns or suburban areas where houses are close together. Thus success can be expected only in the suburbs, in small towns and rural areas. Avoid places where the ground is covered with underbrush, weeds, long grass or tall crops. Pastures, fields, open wastelands, large lawns, cemeteries and golf courses are usually good locations as long as the vegetation is short. Areas of heavy pesticide use should be avoided
Keeping Other Birds From Using the Boxes
To avoid competition from house sparrows, keep bluebird nesting boxes a considerable distance from buildings and to avoid wrens, keep the boxes away from brushy places. Both of these species can gain access to the box through the 1-1/2 inch entrance..
As for the starling, any hole larger than a diameter of 1-9/16 inches will allow it to enter. Thus a round hole exactly 1-1/2 inches in diameter will exclude starlings. The hole must be exactly circular. If the hole is cut a bit lopsided, they can get in. Today, starlings cause problems only where the bluebird uses natural cavities that have large diameter entrances or if the hole there is not circular.
The tree swallow is a competitor too. In fact it is more abundant than the bluebird and thus easier to attract. However, you can lessen the effects of this competition by placing nesting boxes in pairs within 10 to 15 feet of each other. How does this work?
The two species have been found to nest in boxes even mounted back to back on the same pole. Since both the bluebirds and swallows defend their nesting area against others of their own species, there is little chance that both of the paired nesting boxes will be used by the same species. If one box is taken by a tree swallow, the other is left for bluebirds. The swallows and bluebirds seem to get along very well. Remember how John Rogers, mentioned above, has 205 pairs of boxes on his "trail".
Mounting the Box
Use the 1/8-inch holes in the top and bottom of the back piece to wire the box to a post 4 to 5 feet above the ground. If you have only a few boxes, you should mount them on a section of pipe that is 1/2-inch or more in diameter and pounded into the ground. When using a pipe as a support, it is difficult to fasten the box firmly with wire alone. Generally a pipe strap can be used to hold the top of the back to the pipe and wire can be used to fasten the bottom.
If you plan to operate a trail with many boxes, the cost of buying even scrap pipe can be excessive. In this case, you probably should use existing wood or metal fence posts. The wire fastening makes it easy to remove the box if the landowner needs to replace or reset the post. If nails are used to hold it, it is rather difficult to remove the box without splitting the wood.
Do not choose an isolated post in an active pasture since it probably will be used as a rubbing post and. knocked down.
Raccoons a Threat
Raccoons probably are the most serious predators for young bluebirds. If the box is mounted on a metal pipe, greasing the pipe seems to prevent raccoon predation. A person who operates a trail with many bluebirds boxes can save time and expense by mounting the majority of' them on existing posts using wire. If he finds a bluebird is using a box in any stage of the process, he can then transfer that box to a pipe placed near the wood post and the pipe can be greased. Moving the box a short distance will not interfere with the nesting activities. Since most of the boxes are used by other species, only those with bluebirds need to be treated this way if bluebirds, are your main concerns. Sheet metal, cones or collars also are effective.
Since the raccoon must reach into the box and then down to secure eggs or young, increasing the thickness of the front board makes this more difficult. An easy way to increase the thickness is to, take a block of wood and bore the 1-1/2 inch hole in it and then fasten this block of wood with the hole over the existing entrance hole. If a piece of 2 by 4 wood is used, the hole is thus more than 2 inches deep. This makes it much more difficult to reach down into the nest.
The nests should be removed from the boxes as soon as the young have left. This will increase the chances of a second or third brood being raised in the same box. All the boxes should be inspected, cleaned and repaired, if necessary in March of each year. Make sure the drain holes in the floors are open. To clean it, just open the front and scrape everything out with a putty knife.
An excellent reference with more information is an old book, "The Bluebird, How You Can Help Its Fight for Survival by Lawrence Zeleny.
A new one published in 2001 is "The Bluebird Monitors Guide" by Cynthia Berger, Keith Kridler and Jack Griggs. While this is designed for people who operate nest box trails, it has all the useful information that anyone needs who wishes to attract bluebirds with a few boxes.
You may also wish to join the North American Bluebird Society, Box 244, Wilmot, OH 44689 to support its work in preserving the bluebird. Membership entitles you to the group's quarterly publication. The society also sells books as well as nesting boxes and other pertinent publications. Its web site is http://www.nabluebirdsociety.org/
The New York State Bluebird Society may be something you wish to join. Contact Van V. Travis, Jr., PO Box 254, McLean, NY 13102 or check their web site at http://www.nysbs.com/