Greater Yellowlegs, Chignik Lake, Alaska Peninsula, June 14, 2019
Greater Yellowlegs (as well as Lesser Yellowlegs and Wandering Tattlers) are well known as shorebirds that often perch in trees, particularly near their nesting sights, which are on the ground. They are abundant throughout the Chignik River drainage where they primarily feed on various small fishes.
CutterLight 
Since I only experience these shorebirds during migration, I have never had the pleasure of seeing them perched in a tree. Your photo is beautiful.
Thanks! Yes, I think they probably only do this when they’re nesting and establishing breeding territory.