|Starling (most of the time)|
Now that there are so many of them, they often flock together with other birds such as Grackles, Red-winged Blackbirds, Crows and Cowbirds. A flock can encompass 100,000 birds.
An important thing to remember; they are extremely aggressive and often return, the following year, to nest in the same place. You should never allow one to use a birdhouse in your yard, since they will aggressively evict native birds and each other; even killing others' newborns and destroying eggs. A pair of Starlings can build a nest in 1 to 3 days.
After molting, Starlings often show spots (this happens in the winter). Most of the time, however, they are a glossy black. They live anywhere there's food and water except dense forests (this may be because there's too much competition).The jaw/beak, unlike most other living things, is stronger when opening than when closing. So it can pry open tiny cracks (like in tree bark or eggshells).
THE DANGER ZONE. Many birds are killed by crashing into windows. There are situations, however, where it's OK to put a birdfeeder near a window. A feeder closer to a window than 2 feet (including on the window itself) is safe. This is where the bird is in "a landing pattern" and is fully aware of the surroundings. A feeder farther away than 7 feet is OK too.
The "danger zone" of between 2 and 7 feet should be avoided. You may still have a few bird strikes on windows, however, when a bird just isn't paying attention. Like if it's being chased by a hawk, and is looking behind him.