I'm constantly biting and picking at my nails, how can I stop?

My nails always end up uncomfortably short, then once they grow back, I'll start picking at them and biting them, and they'll look terrible, like, unhealthy. I've tried wearing black nail polish, but I had to strip it off because I have birds, and they wouldn't come near me because they didn't like my nails. I've tried to stop myself altogether, but I catch myself doing it, it just happens without a second thought. By the time I catch it, I've already chipped my nail. I really wanna stop, cause I'm sure it's not good for my nails. Any tips would be appreciated.