Bird populations can vary tremendously by location. Some people may never see a bird at or near their windows, while others may see them daily. A relative of mine lived on the 28th floor of a 40 story apartment building in Manhattan. They had a small balcony, just barely large enough to have a small table for 2. Birds would come and peck away at flowers, poop on the railing, and occasionally made "bombing run" flybys that left poop on windows. Only the bottom windows would open, but they rolled up inside, so there was access to the outside--meaning half the time they could clean off the mess by hand easily. Other times it was nearly impossible. I also knew of someone who lived in a building where no windows opened and... they'd have to wait until spring for the cleaning crew.
If you have a nice view, a long term curtain drawn would be a big bummer... not to mention that it cuts out natural light.