This is because the camera was a little confused and exposed for the clouds instead of the crow.
But in some scenarios, you’ll have to more drastically adjust the exposure compensation. For example, let’s say I’m shooting a crow up in a tree on an overcast day. The dark crow is in front of some bright clouds. When I review my first shot, I notice the crow is just a black silhouette against some properly exposed clouds. This is because the camera was a little confused and exposed for the clouds instead of the crow. Since I want to be able to see the details of the crow, I bump my exposure compensation up a couple stops to +2. Now when I take the shot, my subject is properly exposed and the background is slightly overexposed.