I tried something that I've rarely done before. I spent some time at San Francisco's Lake Merced Lake yesterday and found myself quite close to a small flock of Brown-headed Cowbirds. Unfortunately it was about 6:30 PM and with heavily overcast skies, the lighting was very poor.
So, since they were tolerating me so near (within 15'), I decided I'd try my flash. It turned out to work great. The first few shots I took were a little over exposed so I adjusted the exposure down a full stop and ended up with some pretty good pictures.
The flash didn't seem to bother the birds, so I may try it more often in gloomy light.