From page 15 of Better Birding:
Habitat very often dictates behavior. A Northern Harrier glides and swoops low over fields and marshes, periodically flapping and hovering. It behaves this way because it hunts rodents and this kind of low, cruising flight allows it to more easily detect prey. A Harrier’s long wings allow it to pluck rodents cleanly from grassy cover. Harriers have evolved just so, to nimbly take advantage of these open habitats, including during migration. An appreciation of these qualities allows good birders to recognize a Harrier by its structure or movements from considerable distances. Species evolve to take best advantage of their environment.
Better Birding reveals the techniques expert birders use to identify a wide array of bird species in the field—quickly and easily. Featuring hundreds of stunning photos and composite plates throughout, this book simplifies identification by organizing the birds you see into groupings and offering strategies specifically tailored to each group. Skill building focuses not just on traditional elements such as plumage, but also on creating a context around each bird, including habitat, behavior, and taxonomy—parts so integral to every bird’s identity but often glossed over by typical field guides. Critical background information is provided for each group, enabling you to approach bird identification with a wide-angle view, using your eyes, brain, and binoculars more strategically, resulting in a more organized approach to learning birds.