Canon: Inconsistent Exposure, Why?

These 2 photos are 2 photos of flying Sandhill Cranes. Sandhill Cranes are big and heavy birds. They fly slowly. I took these 2 photos less than ½ sec apart. Take a look at the skies. Zero processing, just the defaults applied. So it should be the same. Noooo. Why? Because of the “big because”

I was using Evaluative Metering. The problem, as you can see, is that the top of the birds are very bright, the bottom of the birds are very dark. The wings are huge, from 5 to 7 feet (1.5m to 2m) long. I was pressing on the AF-ON button and tracking the cranes. The focus would go from the black area to the white area and back depending on the wing stroke. So the evaluative metering was adjusting for the change in the brightness of the focus point.

During the exposure reading the EOS 7D looks to see which points, in addition to the selected point, have achieved or almost achieved focus. This information lets the camera know which part of the image is the subject. It then takes metering readings from the zones corresponding to the AF points that have achieved (or almost achieved) focus and combines them with readings from all the other zones.

Quote from Canon, emphasis mine

• This is the perfect example of where I should have used manual exposure. But it was not possible. I only had 2 to 3 seconds to focus, expose, and track the Sandhill Cranes.
• The better exposure system would have been Center-weighted average metering with a +2 over-ride.

My solution? Since I use only one image, fix it in post with Lightroom.