If you don’t know the answer to this post’s title, have a listen to Virginia Water Radio’s latest episode, for the week of August 15, 2016: “Swallows.” The 3 min./55 sec. episode, available online http://www.virginiawaterradio.org/2016/08/episode-329-8-15-16-swallows.html.
Virginia Water Radio’s is a weekly broadcast/podcast produced by the Virginia Water Resources Research Center. The home page is http://www.virginiawaterradio.org. Have a listen or two!