I discovered something as a singer years ago (now that I also play whistle, it's a bit different). When faced with a session or song circle that is almost exclusively guitar and fiddle, as a singer, I try to be patient, but if I feel any hostility towards me, I turn it around by diddling with my voice while their sawing away at some tune. I know most of the tunes and as someone who's been doing Irish "Mouth Music" for over a decade, I can keep up with most of the session fiddlers. Sometimes it drives them nuts - as if I'm invading their territory. Gotta love it.

One other thing I've learned - I have a low voice and have rarely ever sung harmony, it being easier to "harmonize" by singing the melody a full octive lower. But I've been working with someone and I want to do harmonies with him and I've found that playing the whistle has helped. I can find the harmony on the whistle much more easily than I can singing. So often times, I'll figure out the harmony with the whistle and copy it with my voice.