You know, ever since the winter of 2013, I've been noticing a lot more sick and/or injured birds.
During the winter, it's mostly House Finches with conjunctivitis, a common disease both diagnosed in humans and birds, aka pink eye. On humans it's not really bad, but on birds it really is: The eye(s) becomes puffy and swollen, then they eye begins to look wet. It's just downhill after that - the eye gets all crusty. The bird eventually becomes blind, unable to find food, and, in most cases, will die. If you want to know more, visit the House Finch Eye Disease website or the House Finch Disease Survey.
In the spring, summer and fall, a lot of things can happen. Window strikes, fights (especially in the spring), cats, and human development. Just yesterday, my neighbor waved me down while I was going for a walk. "There's a bird here that just hit my window," she said. "It's not moving." When I went over to look at it, I saw it was a Grey Catbird. So I ran home to get gloves (can't be too safe, right?) and when I got back, I saw it had its beak open and some tail feathers were broken. I scooped the poor thing up, and he struggled to get away. I laid him in the grass so we could keep an eye on him. and what was the first thing that stupid bird did? Run into a different window! I tried to pick him up, but he flew across the street and landed on someone's roof. What worried me is that what if that bird was a mother and it had died? Then we would have just lost a generation of Catbirds! Breeding season in the worst time for birds to die. If you want to help prevent window strikes, consider getting decals. And read up on it at Bird Watcher's Digest's How to Solve Window Strikes page or read about Julie Zickefoose's solution.
Fights can lead to serious injuries, but only on rare occasions.
Cats (house and feral) kill over 1 million birds per year. It's really bad during migration, because what if there's some rare species going through your area? Cat + bird = avian disaster. And that's what's happening everywhere. You think your lazy couch potato cat is too couch potatoish to kill birds? Wrong! Even the fattest, laziest cats in the US contribute to this grave cause of many bird species' demise. Here's a stupidly simple solution that should've been thought of a long time ago: Keep your cats indoors! To learn more, visit the American Bird Conservancy's Cats Indoors! campaign. If you want to spread the word, email, go door to door, and/or order brochures.
I won't go into human development because there's a lot of debate in that area, and I really haven't studied enough to have an opinion.
Lastly, if you see a feathered baby bird hopping on the ground, leave it alone! The parents are most likely nearby. For further reading, go to the Northern Illinois Raptor Rehab & Education's I Found a Baby Bird. Now What? page.