I have a few things to suggest. For one, vorona does mean crow (like another person said), so it could come from that, but I think that might be a little unlikely. However, I think you should study the name Voronets more, which is also a last name of some Russian people, though it could have foreign origins. Perhaps it was a nickname long ago. Often times under various circumstances names were changed(such as the birth of an illegitimate child, in which the actual last name of the father would be changed just enough to pay alliegance to the father, but not give it his legal name). Some names were shortened (for example, Putin could have come from Rasputin), others were added on to with different Russian endings, such as -skiy, -ov, -ev, and -in. Hope I helped!