Right? yes? no? I really hope so, as I thought I heard something like that this morning! I went to bed with my window open and was pleased to hear birds, but it didn't occur to me, in the grogginess of morning, to listen specifically for Purple Martins
Martin Colony History: Started trying to attract purple martins in 2012! It's finally happened in 2017! 5 years!!! ASY male and SY female came May 1st, fledged 5 babies!
Unfortunately not the dawnsong.
That's the song when they're slightly annoyed or unsure about something.
Take that same song, and up the urgency and speed, and that's the alarm call (hawks, etc nearby)
Here's a great dawnsong recording along with slideshow, put together by forum member Don Troha: https://www.youtube.com/watch?v=itBN3E0SoZ8