Are you referring to the feral or domestic variations of pigeons? Each has its own distinct characteristics.

If you come across a grey, somewhat chubby, yet small pigeon, it is likely a feral Rock Dove or Rock Pigeon. If its neck lacks the rainbow-like colors and beauty, it does not necessarily mean it’s a female; it could be a juvenile.

On the other hand, if you spot a pigeon that is about the size of a chicken, with a prominent chest and a streamlined body, you’ve probably encountered a racing breed like the American Show Racer.

If the pigeon has an elongated neck, a small head, and a somewhat silly yet endearing face, it is likely a Homer or a Roller. However, it’s important to note that not all rollers exhibit such characteristics. In fact, about half of the rollers I’ve seen resemble regular pigeons, and you wouldn’t know unless you observed them flying high in the sky.

Regarding specific pigeon species, it would be easier for you to search on Google. I cannot provide detailed information on every columbid species here. However, keep in mind that if a pigeon lacks a cere (the fleshy part behind or over the nares), it is probably a dove rather than a pigeon in the strict sense.