digs, dwellings, and dens

bats meet birds

imagine ...bats and birds living together. Often coexisting in snags and artificial structures, these odd housemates get along remarkably well. Most bats and birds work separate shifts - nocturnal and diurnal - and are not at risk of infecting each other since they carry different parasites. The best way to preserve this happy marriage is to save snags. (These standing dead trees are also homes to countless other creatures.) The next best resort is to provide artificial accommodations.

Rather than building separate structures, why not meet the needs of both bats and birds in a single structure with different compartments? The following design will lodge big brown, little brown, pipistrelle, and other colonial bats, plus migratory birds as tree swallows and great-crested flycatchers. With modifications, it will house other cavity-nesting birds, from wood ducks to woodpeckers.

• Use 2 cm (3/4") softwood lumber, such as cedar or pine. Do not use pressure-treated wood. It can be toxic to young bats and birds.
• Cut the front, sides, floor, roof, back and partitions.
• Bore an entrance hole in the front panel (4 cm in diameter for bluebirds and tree swallows, 5 cm for great-crested flycatchers) 4 cm from the top.
• Drill small drainage holes on the side panels, just above the floor.
• Saw shallow, horizontal grooves (2 mm deep and 1 cm apart) on the inner surfaces of the bat section, including the walls and roost partitions, to enable bats to crawl inside.
• Assemble the pieces according to the construction plan, using 4 cm (2") coated flat-head screws and bond-fast glue. The opening between the roost partitions should be 2 to 2.5 cm wide.
• Paint the outside of the structure dark brown or grey.
• In early April, choose a site near a lake, pond, marsh, stream, or river with plenty of insects, ideally inhabited by the species you hope to attract.
• Hang the box 3 to 5 m off the ground on a tree-trunk or, preferably, the side of a building that faces east or southeast and catches the morning sun. The spot should be sheltered from the wind and at least 6 m from neighbouring trees. To prevent house sparrows and European starlings from moving in, leave the entrance to the upper compartment covered until bird migrants appear in spring.
• Have patience. Your structure may remain vacant for a year or two, but its dual purpose doubles the chance that bats and birds will eventually move in.
• Clean the box each fall and ensure that it stays in good repair

hot under the collar
Much to the surprise of wildlife biologists, sheet-metal collars wrapped around trees not only protect nesting birds from predators but also create ideal roosts for bats. Corrugated metal, loosely fitted, allows bats that normally roost under bark to regulate their temperatures by crawling around a tree to the sunny or shady side. Unlike loose bark, these metal collars can by placed where needed and last for years. They should be at least a metre wide, secured along the seam with aluminum nails, and have enough space underneath (two or three centimetres wide) that bats can enter and move around