My iPhone iBIRD app has a similar photo of this bird. It identifies it as a "Shiny Cowbird."

Did you, accidentally and unkowingly, turned on the "video" button? If so, the mirror stays open and locked up.

to LFinger: Thanks. Your recommendations to turn off Distortion Correction and Lens Optimizer are most helpful, especially the manual page references. My 5DMIV now works like a gem, even in low light. I used the 70-200mm 2.8 lens. Others on this issue have made similar recommendations as well. Thanks also to Blurryeyed for bringing this issue to light! gvaldez

Had same experience this past Thursday. Out in the field on a birding trip. Camera's response on the first few shoots was extremely slow, like molasses. Remembered that I had played with the settings. Right then and there went to the Menu setting (wrench icon - yellow, page 5) and selected "Clear All Camera Settings". That did it. Shooting after was up to speed! NOTE: When you select this option - you must re-select important settings. In my case, I had to re-select the RAW file setting, the setting had reverted to jpg. So, yes, I also experienced the same issue. The other reply commentaries are excellent!