I've got a nest box in my backyard and each spring tree swallows will use it to nest and hatch eggs. Here's a picture of the nest box (with two mating tree swallows on top) in May 2010. 2 years ago I put a camera in the nest box to watch them and it went great and I got to see the nest being built, eggs being laid and hatched and the babies developing. Then last year the tree swallows only came to the nest box a few times and never stayed in there for very long and didn't lay any eggs. I believe this may have been due to the number of ants that were in there last year. I put out some Terro ant killer but it was too late.
Now this year I've just recently returned home after being gone for a while and am not quite sure what to do to best encourage the tree swallows to return to the nest box and lay this year. Unfortunately I don't think I ever cleaned out the nest box after last year (though I'm not sure) and I don't know if the nesting material that's in there now is new from this year or still left over from last year. I haven't seen any tree swallows near the nest box, though. Looking at the video from the birdhouse camera I've seen a large spider and one or two ants, so I want to clean out the nest box but due to how late it is in the season already I'm afraid that it might be an active tree swallow nest that I'd be destroying so I figured I would ask here what to do first. Should I empty out the nest box or leave it as is?
In addition, starting yesterday I've seen house sparrows on the nest box every few hours. A male and a female have been perching on top of it every now and then and occasionally poking their head in. One finally went in for about a minute this morning and I was able to capture some shots of it with the birdhouse camera:
I've never had problems with house sparrows before, but after doing an online search on them and learning what they can do to nest boxes, I'm obviously concerned about their presence and what they might potentially do to the tree swallows if they ever come back and nest this year.
Unless anyone here has any better advice, my current plan is to wait until tonight when it's dark, empty and clean out the nesting box completely, put some q-tips with Terro ant killer along the bottom of it to keep the ants at bay and try putting monofilament fishing line around the nesting box similar to what's shown here to hopefully get rid of the house sparrows (while not scaring off the tree swallows). In addition, to hopefully attract the tree swallows back to the nest box I was thinking of cutting a white cream cheese lid into an oblong shape and hanging it from a nearby tree, similar to what's shown halfway down this page.
Please let me know if I should or shouldn't be doing any of this or if I should be doing something else -- I'm still pretty new at this sort of thing and am afraid I might make things worse, so I could use all the help/advice I can get. Thanks!