What's funny is you can really tell the difference between a hawk and a buzzard and see that same difference in the way aircraft are designed. I'm sure this points to ID for somebody, but it's actually good old natural selection.
Hawks have shorter wingspan and a deeper chord (distance from leading edge to trailing edge) This increases roll rate and reduces wing loading during aggressive maneuvers, but increases drag. They also have almost no dihedral when gliding (wings are held flat and parallel), which is the aerodynamic equivalent of toe out: less stable but more responsive. They have a thicker wing profile and a large tail surface, which adds drag but of course increases maneuverability. All this means they need to flap a fair amount and have a mediocre glide angle - they rely on power.
Take a look at a modern fighter jet and note the similarities.
Buzzards, on the other hand, have a higher aspect ratio wing design (longer and skinnier) which is better for gliding efficiency and reduced drag. They also glide with lots of positive dihedral (wings up in a slight V) which is a very stable and self-correcting configuration because it puts the CG below the center of lift. They also have proportionally smaller tails for less drag.
Buzzards are configured for aerodynamic efficiency and payload, like a bomber or airliner, rather than maneuverability, so they can soar for minutes or hours hardly needing to flap.