Your first image is exposed perfectly for a bird that is not in flight and posing for you. But the fact is you should almost never use such a slow shutter when shooting anything that moves or could move especially wildlife and more especially birds. Hummingbirds should be shot with a shutter speed of at least 1/1000th. So you'd have to open up the aperture and increase your ISO to get the proper exposure at that shutter setting. The second and third images are at least 1 or more stops underexposed. When your subject is in the shade and you are using the metering mode that you used, you should think +1 or more on your exposure meter. Take a shot and check your histogram on the back of your camera and adjust accordingly. Sometimes when you need to get your shot off fast, you just guess what the exposure should be for a shaded subject, make that adjustment quickly and hope for the best. But almost always give it a +1 or more. If you use spot metering, then you'll need to practice and figure out what a shaded subject might need to be. But when using spot metering you need to have the center of the focus be on the subject when making changes to your exposure.