I've only seen Black Vultures twice, and both times a handful of them were with large numbers of Turkey Vultures near Cold Spring Park in Woonsocket, RI. The park borders the Blackstone River and is about a half mile from the Massachusetts border. I'm not sure what attracts all the vultures to this particular spot, but I'm sure they have their reasons. During both of my visits, vultures were both soaring overhead and perched on large buildings to the north.
Turkey Vultures (bird code: TUVU) are usually easy to spot. They are large, dark birds found soaring up high, often flapping very infrequently. Depending on the lighting, the trailing edge of their wings appear noticeably pale (note: the photo doesn't show this). They hold their wings at an angle and tend to rock in flight as if trying to maintain balance. Spend a few minutes watching one and you'll see what I mean. Turkey Vultures occur throughout New England where among raptors only Bald Eagles are larger.
Black Vultures (bird code: BLVU) are similarly large, though not as large as Turkey Vultures. In the air, they are distinguished by their stubbier tails, shorter wings, and more frequent flapping. Their wings are also two-toned, but pale only near the wing tips (note: the photo doesn't show this). They are possible in all the New England states, but are quite rare north of Massachusetts.