Yesterday the barn swallows were checking out the windows on the house all day. I guess they knew it was gonna rain again so there'd be plenty of fresh mud for building nests. Well, it rained, and it didn't take 'em long this morning to get to work. Here's the lovely pair on the garage roof right outside the entry window. Notice the one higher up, the male, has his beak full of mud.

They'd already managed to get several trips' worth of mud on the top of the window before I noticed, so I scrubbed that off and applied my "swallow repellent". I learned this trick years ago, when we first began getting plagued with swallows trying to build nests on our house. You have to hang 2 strips of black (and it MUST be BLACK... or maybe dark brown? never tried that) plastic near where they're trying to build. I cut about a 2-inch wide strip off the open end of a garbage bag, then cut it so that it's in one long strip, and tape it from the center to the overhang on the house. When it flutters in the breeze, it must appear to the swallows as other birds or something. But by golly, it works every time!
I had tried numerous other things when we first had the problem... like strips of foil and I don't remember what all else. I actually even resorted to opening a window and shooting one of the little stinkers (shhhh... don't tell on me!) off the deck railing, I was so desperate! Then one day in a little town near here, I noticed a house that had all these black strips hanging from the eaves. I knew who lived there, so I got brave and called her to see if, by any chance, this was to keep swallows away, and more importantly, if it worked. She was happy to share her trick with me and told me that it indeed did work! And I've been doing it ever since! Some years the swallows don't bother the house, but most years they do, and I'm so thankful to have a way to "repel" them (without having to shoot 'em!).
Here's a photo taken after I'd hung the strips (and already replaced the screen). Can't you just see the disappointment in his eyes? I know... I'm so mean....

Someone else is disappointed, too. Willow... she LOVED watching them! Sorry, kitty.
Added note: You may have to play around just a bit with where you hang the strips. Sometimes just one per side of the house will do the job, but if the birds are really persistent, you may need one by each window. I found that where I had hung the above strip wasn't good enough... they brought more mud to the window, anyway. I ended up moving it closer to the window, and that did the trick. Of course, if you have crank-out windows like we do, that may make closing the window without getting the strips caught in it a bit of a pain, but once the swallows have given up, you can move the strips farther from the window.