I've sung plenty of outdoor gigs (including WQXR's appearance last summer at the "Play Me I'm Yours" piano near Columbus Circle, where the video producer was kind enough to cut away at the point when I nearly tripped over a tree root in mid "Amour!"). Outdoor performances proliferate in summer -- and so do the hazards that come with them.
Those start with trying to make yourself heard in the open air, and/or dealing with whatever amplification system there might be. Weather, of course, is a major factor -- and not just the threat of being washed out. Too humid, and your instrument goes out of tune. Too cold, and fingers, lips, or other parts of your anatomy freeze. And when a strong breeze kicks up, woe to musicians who've forgotten clothespins to anchor music to their stands
Then, there's the menace of flora and fauna. Anyone with allergies knows how hard it is to give a performance when your nose's pollen-producing nemesis of choice is in bloom. As for the animal kingdom, so far, I've been luckier than some, who've had insects fly into their mouths while they were going for a high C. But once upon a time, I used to attend -- and participate in -- operas at Washington Crossing State Park, where the amphitheater stage was right next to a pond full of bullfrogs.
Those frogs must have had a sixth sense for tender love duets and tenor arias, because the moment the show kicked into high gear, so did the frogs, "harumphing" to beat the band (but rarely in the correct key). My friend Wendy and I developed a system of keeping score: silly bits of opera staging vs. interruptions from the frogs. The bullfrogs were pretty active, so an opera had to be pretty bad to beat them. I still remember a production of Faust that won, hands down.