We walked a small trail where we found 100s of Barn Swallows and Purple Martins. What I later learned was Barn Swallows frequently built their nests directly below that of an Osprey and live in a mutualist relationship with them. While the Barn Swallow often fall prey to many other raptures, the Osprey are exclusively fish-eater. Osprey are alerted to the presence of predators by the alarm calls of the swallows.
Pictured Barn Swallow ~