I thought this explanation in today's Word was so cool!
[From Middle English, from Middle French terçuel, from Vulgar Latin tertiolus, diminutive of Latin tertius (third). Ultimately from Indo-European root trei- (three) that's also the source of such words as three, testify (to be the third person), triskaidekaphobia (fear of the number 13).]

Why the sense of third in the word for a male hawk? It's either from the belief that the third egg produced a male, or from the fact that the male of hawk is one-third smaller than the female.

Hawks have two groups they are divided into; also interesting words: buteo (essentially, a soarer) and accipiter (kind of like the...uh oh, P 38's(?) of WWII--designed for high-speed maneuverability. In the case of the hawks, following prey (smaller birds) through heavily-wooded areas.

Hawks, thank heavens, have adapted fairly well to cities. One day this summer I watched a broad-wing chase a sparrow from a tree to a bush in my friend's neighbor's yard; then the sparrow fled to shelter underneath the car parked on the street...and the hawk went right under after it!