I've seen people use these bird spikes:
They don't hurt the birds or anything, but it deters them from setting up shop in your gutters etc.
Spikes have their drawbacks.....it's about the only benefit to gutter covers but the negatives outweigh the positive. Just keep the gutters cleaned regularly...where on the house is the gutter they are nesting in? It's kind of unusual. We're happy to clean them for you!
they are nesting in the corner over the porch
I did a search on Hometalk for "birds nesting in gutters" and found a few interesting discussions. One person suggested providing a better nesting place for them. This discussion had some interesting ideas too: http://www.hometalk.com/14719/i-am-constantly-fighting-off-birds-which-peck-holes-in-my-cedar-siding-forget-the