It may be mid-winter, but the nesting season for birds is underway.
Great horned owls and bald eagles are already incubating eggs. Smaller songbirds wait until spring to begin nesting. Those that use in cavities (and nest boxes) get a jump on nesting because cavities provide protection from cold temperatures, wind, rain, and snow.
These species typically begin nesting at least a few weeks before open-nesting birds of comparable size. Among the backyard species that use natural cavities and nest boxes are bluebirds, chickadees, titmice, and Carolina wrens.
Small population
Only about 12 percent of North America’s birds nest in cavities because few species have the strong feet and disposition required to explore deep, dark nooks and crannies. It takes a fearless, acrobatic bird to explore cavities where predators may lurk.
The best way to attract cavity nesters is to place nest boxes in suitable habitat. For example, pastures, hayfields, cemeteries and golf courses are ideal for eastern bluebirds. Forest edges attract chickadees and titmice, and Carolina wrens often stay close to homes and sheds.
The supply of natural cavities is limited so competition for these nest sites is intense. Because cavities provide protection from the elements, hole-nesters can begin nesting sooner than open-nesting birds. This means they often fledge their young before a major predator — tree climbing snakes — becomes active. Consequently, cavity-nesters usually have higher nest success than open-nesters.
Another advantage that cavity-nesters enjoy is that the young stay in the nest longer. Bluebirds and chickadees, for example, stay in the nest for 17 to 21 days. This compares to open-nesters such as cardinals and robins, which fledge at just 10 to 12 days of age. When cavity-nesters fledge, they are larger, stronger, and can fly. It takes most open-nesters three or four days to get strong enough to fly after leaving the nest.
Winter work
While it’s still too nasty to spend much free time outdoors, build a few boxes for backyard cavity-nesters. And get the kids and grandchildren involved. A basic nest box measures four or five inches square (inside dimensions) and 10 to 12 inches high. The entrance hole should measure precisely an inch-and-a-half in diameter and be placed about an inch from the top. This hole size prevents bigger-bodied starlings from using the boxes. The front or side should flip open for easy cleaning.
Tips
Hang nest boxes five to six feet above the ground on a post protected from below by a predator baffle. The baffle is essential because unprotected nest boxes eventually become raccoon and snake feeders.
Here are a few more tips to keep in mind:
- Use three-quarters inch stock to insulate nests from spring chills and summer heat. Any untreated lumber will do, but exterior plywood is relatively inexpensive and weathers well.
- Assemble with galvanized screws to extend the life of the box.
- Put a shingle on the roof; it receives the greatest exposure and weathers faster than the sides. Do not paint the inside of the box.
- Extend the roof at least five inches over the front of the box to protect the hole from wind-blown rain and marauding paws. Drill four quarter-inch drain holes in the floor.
- Never put a perch on the outside of a box. Cavity-nesters have strong feet and easily cling to vertical wooden surfaces. A perch is an invitation to invasive house sparrows to use and defend the box.
- Finally, boxes should be in place by mid-March. Use plastic coated electrical wire to strap boxes to posts. Hang boxes so they will be shaded during hot summer afternoons, and orient the hole to the east to avoid prevailing winds and driving rain.
For detailed nest box plans for a variety of species, visit www.allaboutbirds.org and type “nest boxes” into the “find” box. Nest boxes can be purchased at wild bird stores and nature centers. The Pennsylvania Game Commission also sells a variety of affordable nest boxes; a set of two bluebird boxes, for example, costs just $32, delivered.
To order, call 1-814-355-4434, or visit www.pgc.state.pa.us and click on “Howard Nursery” from the “General Store” drop down menu and then select “Wildlife Homes Order Form.”
