CHICAGO (CBS) — Naturalists in Aurora have asked for some help in its effort to make the world safe for a dwindling bluebird population.

Fox Valley Park District spokesman Jeff Long said they are looking for monitors for some 30 to 40 bluebird boxes, or birdhouses.

“They’re cavity nesters, as we call bluebirds. So they can’t make up their own nests. They have to seek out areas with tree stumps, those types of areas. That’s why we put the bluebird boxes out there,” he said.

Long said a 90 percent drop in the nation’s Eastern Bluebird population over the past few decades has driven the district’s effort to put up houses for the birds, and find people committed to watching them for several weeks, until the young can fend for themselves.

“They’re like landlords for the birdhouses, and just make sure there’s no sparrows or starlings, which tend to go invade the bluebird house after they’ve already laid their eggs,” he said.

Long said sparrows and starlings also like to take shelter in the bluebird boxes, so he’s trying to sign up monitors to boot out the invaders, and give the bluebirds a chance to set up shop in and around Aurora.

“They’re invaders, or predators, and they would invade the bluebird box and take it over for themselves, and the bluebirds have already established in there, and done up their nests, and laid their eggs. They usually lay three or four eggs,” he said.