Roosting boxes for cold nights

As colder weather approaches, I often get questions about winter roosting boxes. Many cavity-nesting birds roost (that is, sleep) in natural cavities, nest boxes, or specially designed roosting boxes. It sure beats sleeping out in the open on cold winter nights.

Bluebirds, chickadees, titmice, nuthatches, and Carolina wrens nest in cavities and readily use nest boxes, but they also sleep in natural and man-made cavities on the coldest nights of the year.

There is no better place to avoid plunging temperatures, howling winds, and blowing snow.

On frigid nights, a cozy roost site can mean the difference between life and death for cavity-nesters. You can make winter more bearable for these birds by building or purchasing a roost box.

Some observers have reported as many as 10 bluebirds cramming into a nest box at dusk in mid winter. I’ve personally seen as many as a half-dozen bluebirds retire to a nest box on a cold winter evening.

There are also reports of as many as 46 winter wrens, 50-plus pygmy nuthatches and 29 white-breasted nuthatches roosting together in single cavities. They gather to sleep and conserve body heat on the coldest winter nights. On milder nights, they perch among the protective cover of evergreen vegetation or persistent dead leaves clinging to an oak branch.

This pattern holds for many cavity-nesters. On warmer nights, they roost in vegetative cover; on colder nights, they sleep in cavities. Woodpeckers and some owls, on the other hand, usually sleep inside cavities, regardless of the weather.

Roosting behavior gives backyard birders another opportunity to provide a critical resource for cavity-nesters. But understand that this applies only to cavity-nesters. Open nesters such as blue jays, cardinals, and mourning doves find shelter in dense vegetation.

Though cavity-nesters frequently roost in ordinary nest boxes, this may be simply because better roost sites are unavailable. Nest boxes are typically well ventilated; the entrance hole is positioned at the top of the box. Vents promote heat loss (which is good during the hot nesting season), and the entrance hole allows heat to rise and escape.

Designed to minimize these problems, a roost box measures approximately eight inches square and 24 inches high. There should be no air vents, and all upper joints can be sealed with a silicone bead to completely eliminate air flow. The only opening is a two-inch entrance hole cut into the bottom of the front panel.

Inside, a series of shelves or quarter-inch dowels runs from side to side. The dowels should be staggered to minimize the droppings that fall from birds perched above to those perched below. Finally, be sure one side of the box is removable so it can be cleaned out occasionally.

Hang the roost box five to eight feet above the ground in an open southerly exposure to take advantage of solar radiation, and if possible, place it so it is protected from the prevailing winds.

If you erect a roost box, don’t expect immediate results. Birds need time to discover a new roost site. Ways to determine if a roost is being used include checking the floor for droppings and watching for birds leaving the box at dawn.

Another option is to modify ordinary nest boxes for the winter. First, remove all old and soiled nesting material from used boxes and replace with a one-inch cushion of dry, insulating grass. Then plug all vent holes with a pliable, putty-like material that can be easily removed in the spring.

Finally, I must add a word of warning. During periods of extreme cold, especially following an ice storm, birds sometimes die while roosting. This is natural and unavoidable, though it can be shocking to find a box full of dead birds in the spring.

Though roosting boxes have been around for years, surprisingly little is known about how much birds use them.

The logic behind roost boxes is sound, but I would love to hear from readers who have experience with roost boxes.

For detailed winter roosting box plans, visit Cornell’s Lab of Ornithology web site, www.birds.cornell.edu, and search “roost box.”

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Dr. Shalaway can be heard on Birds & Nature from 3 to 4 p.m. Sunday afternoons on 620 KHB Radio, Pittsburgh or live online anywhere at www.khbradio.com. Visit Scott’s website www.drshalaway.com or contact him directly at sshalaway@aol.com or 2222 Fish Ridge Road, Cameron, WV 26033.

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