Group’s Experiments Seek the Perfect Bluebird House

A wildlife researcher with the Brice Prairie Conservation Association uses temperature data loggers to guide the construction of ideal houses for bluebirds.

Sometimes it isn’t easy dealing with Midwest weather, particularly those abrupt changes in temperature.

Think what it would be like without screens to keep bugs outside, without heating during freezing nights, and without air conditioning when the temperature tops 90 degrees.

That’s what a bluebird faces during its stay in Minnesota and Wisconsin. The nest boxes we provide for bluebirds to nest, lay eggs, and incubate and fledge their young are usually wood boxes, without heat, only air ventilation, and usually no screens on any vent openings to keep black flies out.

Leif Marking, a member of the Brice Prairie Conservation Association, and several other members and volunteers continue to experiment to determine the best bluebird house.

As soon as Marking solved the early-summer black fly problem by closing off all the vents, along comes a 100-degree day that could be lethal to young birds. Even before that, sometimes there is a night that dips below freezing, just after the first clutch has hatched.

Marking, Fred Craig of the Brice Prairie Conservation Association, and Cindy Koperski with the Wisconsin Department of Natural Resources conducted some elaborate experiments from April 15 through August 31 last year. They measured the air temperature inside various bluebird nest boxes, some that were modified to provide shade and others with vents or no vents.

Hourly temperatures were recorded in 10 houses using HOBO Pendant Temperature Data Loggers. No birds were allowed to nest in these houses. They were kept out by placing screen over the oval openings.

Shade panels were installed on several houses to deflect sunlight.

After examining the data from these experiments, Marking believes he is headed in the right direction.

“I build all my houses as convertible houses now,” he said. "In spring, the vents are closed, except for the oval opening where the birds enter. Then, in summer, the houses are vented, if necessary."

Screws are used, rather than nails, to attach the two side panels to the back and front of each house. The left side panel is fastened with four screws. The right side is fastened with only two screws, which allow the panel to be opened for cleaning and inspection.

"In spring, the two side panels are all the way up to the roof, with no room for ventilation," Marking said. "This keeps the house warm and keeps the black flies out."

If the weather gets too hot for the second or third nesting during summer, the screws holding the panels can be removed, and the panel slid down a half inch, creating a vent and the screws replaced at a lower point.

"I pre-drill where the screws are going to be for the lower setting, so all the work can be done in the field without removing the box from the post and without any danger of splitting the wood panels with new screw holes," Marking said. "The adjustment can be performed even if there are eggs or baby bluebirds in the nest."

Marking said that in general, if 50% of the birds survive, it is considered successful.

"If we could make that 75%, just by some manipulation of the nest box, that would be a great improvement," he said.

To reduce temperature extremes, Marking's club makes all the houses they sell using 7/8-inch cedar, not ½-inch plywood. This provides better insulation from heat and cold.

"I don’t recommend painting the houses either," Marking said. "Paint will destroy the breathing power of the wood. If a dark paint is used, the house will absorb more heat in summer, too. Cedar will last 15 to 20 years without paint, so why paint them?"

Marking has already checked and cleaned hundreds of houses, and recommends everyone do the same before the birds begin assembling their nesting materials inside.

Courtesy of
Written by Jerry Davis