Bluebirds commonly nested in cavities in trees or fence posts, said Lehigh Gap Nature Center Director Dan Kunkle. Each year the Center holds a bluebird house-building project. Today, orchard trees are small and posts are metal so there are fewer natural nesting sites and a decline in the number of Bluebirds occurred.

In the 1960s Bluebird housing was begun to be provided. A house occasionally was occupied as soon as it was put up.

Competition from introduced species competes with them for the few remaining sites. The English or House Sparrow likes farms with lots of buildings that may provide nesting sites.

The European Starling is too large to fit into standard manmade Bluebird houses.

Either of these birds can be evicted, though if what you consider the wrong native bird chooses the Bluebird house, they must be allowed to raise their young. Among the most common native birds that may choose a Bluebird house are Tree Swallows, Black-capped Chickadees, Tufted Titmice and Wrens.

On Feb. 23 the pieces for 12 Bluebird houses were spread on the tables in the basement ready to be made into homes for birds.

Bluebirds prefer open areas and are one of the few birds that look for insects on a mown lawn. They are also territorial and will not let other Bluebirds nest nearby. Other birds are okay because they will not compete for the insects on the ground.

The houses should be placed at a height of between three and five feet. A four-by-four makes a good post.

They are not disturbed by someone checking the nest for eggs or baby birds but this should not be done on a cold, rainy day because the mother's warmth is needed. If she leaves only a short time it may be dangerous for the eggs or babies.

It is good to allow nesting material to remain in the house over early winter because some Bluebirds do not migrate and may use it for winter protection. In late February clean the house by scraping the old nests and parasites out of the house. Bluebirds will begin looking for nesting sites shortly thereafter.

Kunkle said he loves seeing the bluebirds in winter because they provide a spot of color in a drab season.