Signs of a sick bird — what to watch for

I'm a newer bird owner and I know birds hide illness. What are the early warning signs I should be looking for with my Senegal parrot? I want to catch problems before they become emergencies.

This happened to us last winter. I think the shorter days and dry heated air were the cause for my bird.

I've had birds for 15 years and I've seen this many times. In my experience it usually comes down to dry winter air from forced-air heating.