Taxonomy is the attempt to place all plant and animal species in a logical order based on relationship. Two thousand years ago. Aristotle classified birds by appearance and behavior, such as birds that swim, birds of prey, and birds that sing.
More recent ordering of bird species relied on anatomy—analysis of physical characteristics—to trace descent from common ancestors all the way back to the very first bird species. Field guides to the birds follow the modern taxonomic order from "old" to "new" species based on that shared ancestry. Ducks, geese and swans come first in the field guides as the first grouping to evolve.
Songbirds come last as the newest species. Admittedly, "new" is measured in millions of years—back to the time of the dinosaurs. The most recent approach, DNA analysis, goes beyond anatomy and occasionally comes up with some major surprises.
One of the most recent taxonomic changes is also one of the most unexpected. DNA sequencing indicates that falcons are more closely related to parrots and our backyard perching birds than to hawks and eagles. The mighty peregrine falcon, universal symbol for predatory speed and power, now shares taxonomic company in-between woodpeckers and parrots. How strange is that?! Falcons continue to occupy the bird-of-prey niche with hawks and eagles. Over the millennia they have evolved the grasping talons and hooked bill that dispatch prey with efficiency—but not because of close kinship. Evolutionary history is a timeline almost beyond comprehension.It adds up to millions of generations and incremental changes that in time form widely diverging branches on the avian tree of life.