Hoo, Squadron Hawk in blue? Quite a format-defining statement you're making there. I think this ability is more within white's pie than blue's, though any colour can get it.

Swarm as a mechanic led to card's like Matriarch's Emblem and (((Patriarch's Signet))). Since Squadron Hawk is in white, and I'm trying to avoid swarm-like mechanics in white and black, blue seemed to be the best fit.

Ah, yes, okay, I can see why you want to keep it out of white.

Green has more history with this effect though: Pack Hunt, Bifurcate, and the Howling Wolf cycle. But, like I say, every colour had it in Onslaught - blue's one was Screaming Seahawk - so you can put it wherever you like with at least some justification :)