I have to adjust my exposure compensation to some degree about 90% of the time. Dark birds with bright backgrounds get underexposed and bright birds with dark backgrounds get overexposed. Here are some examples where I had to adjust the exposure compensation...
In this osprey image you can see I had the exposure compensation set to -.7 (which is -2/3rds). Unfortunately it was not enough. I tried to fix it the best I could in lightroom but the whites on top of the head are clearly blown out. I should have set it to -1 1/3rds.
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In this image the background was bright and the bird was dark which means the camera will most likely underexpose the image. So I set my exposure compensation to +2/3rds. It blows the background out but the bird is exposed properly (could have raised it a little more too).
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The same in this image. I had to set it at + 1 2/3rds to show some details in the darker areas of the cormorant. I probably could've bumped it up a tad more.
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You always want to take a test shot as soon as you can and see how your exposure is. You can look for blinkies if your camera shows them or you can look at the histogram and make sure you have data in all sections without having any data at the far right or left sides meaning either the highlights or shadows are getting clipped. But in high key and low key images, you will have data up against the edge and you really have to look at your subject to make sure it is exposed properly.