The two most common bird species in Kanto, most everyone has trained them at some point or another.

I built Pidgey mainly based off of a shrike, besides its voice, it really doesn't strike me as very pigeon-like. I figured a small predatory bird would better suit a species that evolves into huge raptors. It's mostly docile and keeps to itself, only really attacking when it feels threatened.

Spearow here is pretty much a small hawk. Compared to Pidgey, it appears quite flashy, territorial, and aggressive. If a single Spearow can't drive away an annoyance on its own, its entire flock will quickly come to assist it. This one picked out a prime perch on a Lum tree, and seems a bit miffed by the Pidgey landing too close.

In case it isn't obvious, this is an homage to Audubon's birds. It probably wouldn't be too difficult to find the exact painting I based it off of, if you're curious.