If they have a reliable food source near your house, they will return to somewhere near the food source. They eat sugary items, meat and other insects. If you have standing water where mosquitoes breed (in my case they hang out near the entrance to my honey bee hives and scavage the dead bees my honey bees clean out of the hive), open trash cans, recycle bins with soda cans, they all attract YJ's.

I have different birds then you. I have Ann's year round. Right now I have a bunch of boys, no nesting likely with this crew. Last year I had a yard full of babies. How can I have all these babies and not adults? I thought maybe I was stealing the neighborhood babies because of my feeders. I found an old log of 'Lady in the Lamp'. This bird had several broods a summer in a lamp. The condition of the nest would be good since it was well sheltered and so she reused it again and again. It dawned on me that I had returning Mom's last year that probable had multiple broods and everyone stuck around for the summer. All those babies were mine! I just bought a couple more feeders as I am hoping for a crowd this spring. I have no hope of ever finding a nest. I saw one in a garden center at Home Depot. It had caution tape wrapped around the bush is the only reason I saw it. The nest was a tiny little bag thrown over a limb. Mom carefully came in the back way. I am content to see the babies come to the feeders. The wild tail contortions it takes them to navigate tells me how new to the wing they are. Here is a link that might be useful: Lady of the lamp.

They won't use it again next year.... extension.iastate.edu: Preserving and Displaying Bald Faced Hornets Nest - The easiest method of collecting a nest is to wait until after the hornets have abandoned the nest in the fall (after the first hard freeze or by late October). Collect the nest as soon as possible because exposed, unprotected nests are subject to destruction by wildlife and weather. There may be few, if any hornets in a nest collected in late fall. If you feel the need to be extra-cautious, leave the nest in a garage or porch where it will be protected from the weather until mid-winter. Then bring the nest indoors for display. Leaving the nest in the garage also eliminates the slight risk that the carcasses of hornets and larvae that remain in a collected nest may produce a mild odor before they completely dry up.

Being how rare you say they are in your area, I am sure you want to make sure the Bluebirds stay and successfully raise their young in your yard. To do this you need to remove that box from that tree immediately and get it at least 15 ft away from the tree mounted on a slick metal pole (electrical conduit works best) and preferrably with a predator baffle. Raccoons and squirrels can and will get into the nestbox where it is mounted now. A Raccoon will even eat the mother bird if she is in the nest when they make their raid. Check out sialis.org for lots of useful information on Bluebirds and other cavity nesting birds. For the bluebirds sake I hope you take this advice. If they want this box, moving it will not interrupt their nesting. You can wait a few days until she is done making the nest but do move it before they eggs are laid if possible. Bluebirds will give you hours of enjoyment however if the nest fails they will leave your yard in search of a new nesting site. Good luck! Donna