DEAR JOAN: Over the last couple of months, birds have been aggressively removing fibers from my window screens on the second floor of my house. My screens are not metal, but some kind of thread-like material.

My assumption is that they’re using the fibers to build their nests. Most of the damage is about 6 inches from the bottom, cut straight across from end to end. I must admit that their handiwork is quite impressive.

Though I’ve tapped on the windows repeatedly to scare them away, they’re very persistent and not deterred for very long. During my neighborhood walks, I’ve seen the same destruction on nearby houses.

Do you have suggestions for discouraging this behavior? Ultimately, I’ll probably replace my screens with those made from metal, but in the interim, it would be nice to find a solution to avoid further damage to the existing screens.

Might a faux owl or some other species be a deterrent? Any other suggestions?

Jerry Isaac, San Jose

DEAR JERRY: The birds are most likely raiding your screens and those of your neighbors to gather nesting material.

A kind solution would be to provide them with an alternate source. You also could replace your screens now and leave the old ones out for the birds to cannibalize to their heart’s content.

One method to keep them away from your windows is simply to hang something reflective near the window, which will move with the wind. This could be a Mylar balloon, securely tethered so it doesn’t fly away, or old CDs. Remember when we used to get AOL discs in the mail three times a week? Those were great as bird deterrents.

If you don’t want to leave it to chance, stores that specialize in wild birds carry a variety of products for scaring birds away from areas.

An owl or peregrine falcon statue might work, but my experience is that the birds soon realize that glaring Mr. Owl is no threat to them, and they resume their activities.

DEAR JOAN: I saw something surprising and thought you could shed some light on it.

A small bird hit a window of our house. I’m thinking it was being chased. I went outside to check on it and saw a large black bird — it looked like a large crow — standing over it, picking it up in its beak. It then flew off with the small bird. At that point, it was hard to tell if the small bird was alive or not.

What gives? I didn’t think crows were meat eaters. It would be wonderful if crows offered emergency ambulance service to bird hospitals, but I’m not counting on that.

Ron J., San Jose

DEAR RON: I’m so relieved that you aren’t counting on crows to perform emergency medical transport, because what really was going on was the exact opposite of that.

The crow was most likely pursuing the smaller bird, which in its frantic attempt to escape, crashed into the window, killing or stunning it. The crow then captured its prey and flew off for lunch, or brought it home to feed its young hatchlings.

Many birds, including corvids, the family crows belong to, are carnivores. That’s one reason crows and scrub-jays are so disliked — they often prey on baby birds and eggs.

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