Wintering Bluebirds in Southern Illinois

January 3, 2022

By Will Summers, Master Gardener

“Birds fly south for the winter” is an axiom that has been accepted for many years and applies to a lot of bird species. Based on their mobility, for many bird species this is true. Lately, bluebirds remain farther north in winter months indicating that not all bluebirds are following our rules. Here we draw your attention to this phenomenon and offer some recommendations to assist in bird survival during cold winter months.

Bluebirds are mostly insectivores, “insect-eaters”, for most of the summer breeding season, but in the winter when few insects abound, they turn to fruits. Food, primarily berries, account for the majority of the bluebird’s winter diet. The following is a list of berries available to bluebirds in south-central Illinois in winter: red cedar, sumac, Virginia creeper, poison ivy and hackberry. Surprisingly, several non-native plant species, available and eaten in winter by bluebirds, are holly, bush honeysuckle and Japanese honeysuckle.

Bluebirds need shelter and cannot survive wet, freezing nights without shelter. Many times, dense vegetation, such as eastern red cedar and other dense evergreen shrubs, provides acceptable cover, but windy conditions with freezing temperatures may drive birds to seek more protection from the elements. Since bluebirds are cavity nesting birds in summer, it is only natural that they seek out tree cavities for protection in winter. Natural tree cavities provide shelter for birds, but these are becoming scarce and in fierce competition from other wildlife.

Bird houses and artificial winter nest boxes harbor and protect bluebirds during the brief cold-snaps that occur even in the mildest winters. Several bluebirds are known to shelter together in a cavity at one time. Now is a good time to consider building a winter bird box. The basics are different from the typical “birdhouse” used for spring or summer nest boxes.
Winter bird boxes have the entrance at its floor or lowest side. As with nest boxes, winter bird box entrance size is critical to exclude other larger birds or animals. The correct whole diameter for bluebirds is 1 1/2 inches. The low entrance allows warmer inside temperatures and less heat loss. Add a entrance shelf or platform for birds to arrive and depart the opening. Use thicker wood and insulation board on the roof and sides as to retain warmth. The interior size should be slightly larger for wintering birds. Add a few perches inside. Use natural tree twigs as wooden pegs or 3/8ths inch dowel to accommodate several birds roosting at one time.

Locating the winter bluebird box in full sunlight, at least part of the day, is important. Point the opening away from prevailing winter winds from the north and west. Entrances facing south are best and in a sheltered location utilizing natural windbreaks of trees and tall shrubs or even buildings is important. Winter bluebird boxes that face south will receive more winter sunshine and stay dryer and warmer. If mounted on a post or tree, keep the box 8 to 10 feet off the ground and include a predator guard to deny predators access to the birds.

Consider doing things this winter to benefit winter bird survival. Winter birds, including bluebirds as well as tufted titmouse, Carolina chickadees, Carolina wrens and some smaller woodpeckers, need the shelter of bird boxes. For more information relating to wintering birds, please contact your local University of Illinois Master Gardener, your county University Extension office or your nearest public library.

Native plants such as juniper berries provide nourishment for wintering birds.

An artificial shelter can aid non-migrating birds in winter



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