Falco peregrinus) that was perched on the same tree, same branch.
And through the magic of Photoshop, here they are perched side-by-side. The trees don't line up exactly because the two photos were taken from slightly different positions, but what fun nonetheless.
Here are the size stats for the two species, from The Sibley Field Guide to the Birds of Western North America: Merlin-L 10" WS 24" WT 6.5 oz (190 g); Peregrine-L 16" WS 41" WT 1.6 lb (720 g).
And now, photographic verification. Peregrine is bigger. A lot.