By REBECCA SLOAN

By REBECCA SLOAN
VINDICATOR CORRESPONDENT
HEY'RE A SIGN of good luck and a reason to smile.
With one flash of their sky-colored wings, they can brighten even the grayest of days.
What is it that makes bluebirds so special?
Whatever it is, plenty of folks want these feathered treasures living close by, and they'll go to great lengths to lure them to their back yards.
But putting up a bluebird house can be far simpler than persuading a bluebird to actually take up residence.
"The key to attracting bluebirds is to put bluebird nesting boxes in the correct habitat," said Patty McHenry, bluebird expert at Mill Creek MetroParks. "You can't just put a bluebird house anywhere and expect a bluebird to nest there."
The right dimensions
Ric Mattmuller, a local representative for the Ohio Bluebird Society, said the dimensions of a bluebird house are equally important.
"Bluebird houses can be made from a variety of materials, but they should be at least 8 inches tall and 4-by-4-inches wide. Also, the circular or oblong entry hole should be no wider than 11/2 inches," Mattmuller said.
A larger entry hole will invite starlings to set up house, and starlings are a menace to bluebirds.
"A starling is an imported species that is also a cavity nester. Starlings will go into a bluebird house and kill the babies and tear out the nest if they can squeeze into the nest hole," Mattmuller explained.
Other bluebird home wreckers include the house sparrow, the tree swallow and the house wren.
"The house sparrow is just as much trouble as the starling. It has a short pointed beak that it uses as a weapon to kill both young and adult bluebirds. It will also destroy nests," Mattmuller said. "If you see a house sparrow trying to build a nest in your bluebird house, remove the nest. You might have to do this more than once, but it will keep the sparrow from establishing itself in the house."
Less of a menace
Tree swallows don't pose as much of a threat to bluebirds.
"Tree swallows eat insects that they catch flying in the air, while bluebirds eat insects that they catch on the ground, so there's minimal competition for food. Tree swallows are also less of a menace," Mattmuller said.
House wrens can behave aggressively and can invade bluebird houses, but most house wrens prefer wooded areas while bluebirds like wide-open spaces.
"Also keep in mind that while it's not illegal to disturb a house sparrow's or starling's nest, house wrens and tree swallows are protected by the federal government," McHenry said.
Charming chickadees or docile tufted titmice might also make themselves at home in bluebird houses that are close to woodland settings, but McHenry doesn't mind.
"They are wonderful birds. Not in the same category as the house sparrow or starling and also a protected species," she said.
Bluebirds don't mind sharing their territory with other bluebirds, but bluebird houses should be at least 300 feet apart, McHenry said, and boxes should be about 5 feet off the ground.
Although some people mount their bluebird houses on wooden posts, McHenry recommends using a metal post.
"A raccoon or a snake can easily climb a wooden post and have the bluebird babies or eggs for a meal," she said.
Some people design bluebird trails along several acres and erect as many as 100 bluebird houses.
McHenry has placed about 50 bluebird houses at different locations throughout Mill Creek MetroParks.
Woodlands were the original habitat for Eastern bluebirds, which is the type native to Ohio and Pennsylvania.
They adapted
After the pioneers cleared the land and fenced it in, bluebirds adapted by building nests in rotting wooden fence posts and apple trees.
"Bluebirds loved to nest in orchards in the cavities of old apple trees," McHenry said.
When the wooden fence posts of yore were replaced with metal fence posts, bluebird populations declined.
"Bluebirds have really had to adapt to all the changes in the environment. Now the species is making a remarkable comeback largely due to the efforts of people who are putting up bluebird houses and monitoring nests," Mattmuller explained.
Bluebirds can have as many as three different batches of babies per season with as many as five eggs per clutch.
"Three clutches of eggs per season is possible, but two is more common," McHenry said. "You can put up a bluebird house now -- in July -- and possibly catch a pair that's looking to have its second set of offspring."
Migration habits
During winter, most bluebirds don't migrate farther south than Kentucky.
"Many bluebirds stay in Ohio all winter, but you often don't see them. They go deep into the thickets, where there are plenty of berries to eat," McHenry said. "Sometimes if we have a really cold snap, you can find as many as six bluebirds huddled in a nesting box trying to stay warm."
Males will often start scouting out a nesting spot during early spring.
"Sometimes a male bluebird will start to build a nest in many different nesting boxes and then show the different boxes to the female and let her choose the one she prefers," McHenry said.
Bluebird young will return each spring to the place they were born.
Although bluebird hens often lay their first clutch of eggs in early spring, that first batch of bluebird babies often doesn't make it because of cold weather.
The second or third batches have a better chance of survival, Mattmuller said.
Hot, sizzling weather doesn't pose as much of a problem for baby bluebirds, though the temperature inside a bluebird house can become stiflingly hot during the dog days of summer.
"It's a good idea to make sure your bluebird house has air vents at the top to let out some of that heat," Mattmuller said.
Another discomfort that comes along with summer is blowflies.
Mattmuller said blowflies are attracted to fecal matter inside bluebird houses.
"The blowfly will come along and lay its eggs inside the bluebird house. Then the larvae will hatch and will attach to the baby bluebirds and suck their blood. The parents don't seem to notice the larvae, so they won't remove them from the babies. This can eventually kill the young bluebirds," Mattmuller said.
Mattmuller encouraged people with bluebird houses in their back yards to check for blowfly infestations.
"If you see blowfly larvae in the nest, open the box and gently remove the larvae if possible," he said.
McHenry said blowfly larvae -- or pupa -- are about the size of a potato bug.
Mattmuller said it's a myth that if a human hand touches a baby bird or a bird's nest, the parent birds will abandon the offspring.
"Bluebirds won't care if you touch the nest," he said.
Bluebirds will care, though, if they see you hanging around the nest box all the time.
"Bluebirds like their privacy. They are shy, and they can be selective about the place they call home," he said.
The lure of food
One way to attract bluebirds to your back yard is to distribute some of their favorite food -- mealworms -- in select areas or special bluebird feeders.
You can buy mealworms at pet stores or specialty stores like Wild Birds Unlimited.
McHenry said people have differing opinions on whether of not bluebird nests should be removed at the end of the season.
"You definitely don't want to remove the nest too early. The bluebirds might want to use it for another clutch of eggs. I wait until fall and remove the nests from my nest boxes. Bluebirds do like to build new nests in the spring," she said.