Bedelia,
I had put up fishing line on one of my boxes even before they started to build a nest,it did not even phase them,as a matter of fact they started the nest the next day.I doubt it scared them away,how long has the nest been completed,I find that my pair will lay the first egg around 7-9 days after completing the nest.They may be around ,you just don't see them.Look for them first thing in the morning around the box,they should come to check the box fist thing in the morning.Keep us posted.

Matt

I've never had birds leave because of it. Not even the hosps.

The BBs are never bothered by fishing lines.They might be visiting the nest early in the AM.When they are ready to lay the first egg, they will be back and then, only to lay the egg and then they don't hang around until it is time to incubate.If you have trees close to the nest box, you might see them sitting on the trees after sunset,guarding the nest.
michelle

The nest was there for 8 days, and they were around a lot. Now I don't see them at all, but then I'm not watching 24/7 (not quite anyway).

My husband said I scared them off, but the way I figure it is if I didn't put the monofilament up, the HOSPS would kill them. So if they found another safer nest, it's better for them.

I'll check again to see if there are any eggs in it. If not, should I leave the house alone or remove it? Is there a chance some more BBs might come by, or is it too late now? I live in upstate NY.

Thanks for the encouragement.

Watch for them early in the day, that's when most nestbuilding occurs. Egg laying also usually occurs in the early part of the day, so check the nest later in the day, after noon.
Hey, the Eastern Bluebird is your State Bird! Don't give up on them.
It can be difficult to tell if nest material has been added or rearranged. You can take pictures with a digital camera and compare them, or place a long piece of grass in the entrance, to see if it gets removed.
Bluebars

Is this the same box that is mounted on a tree? If so you should remove it now and mount it the proper way on a metal pole w/preditor baffle.

I always thought nothing should be added to a box until AFTER the first egg was laid or run the risk of spooking the bbs off.

yes, it is the same box that was on the tree.

According to what I read on the sialis.org site, the sparrow spooker should not be put up until after an egg is laid. It recommended the monofilament before the eggs are laid.

I did check today and there are no eggs in it. After 2 whole days of not seeing them, I'm afraid they're gone. My husband just wants to take the box down, but I'd like to keep it up just in case.

So you did remove it from the tree and mount it on a metal pole?

Sometimes the female doesn't start laying eggs right away. Sometimes she does, it depends on the female. Mine always started laying the nest day after nest building was completed and they never hung around a lot even while the female was laying eggs. You'll just have to wait and see what happens.