Peregrine with kill

Nikon D4
1/400
F/6.70
ISO 800
600mm + 1.7 tc + 1000mm
Aperture Priority
Center Weighted avg
WB auto
Cropped 77%

Male peregrine falcon beheading a kill before taking it back to the nest. He plucked feathers but mostly wanted to pull the head off the kill. Once he beheaded the kill he immediately turned and flew to the nest. Not sure why. It appears that the head has lots of usable protein but it was never consumed. The male never came back to eat the head.
This was taken in poor conditions with low light. I was using a 1.7 extender for this shot and only got 1/400 of a second shutter speed shooting wide open. I also was using aperture priority which I almost never use because conditions were changing constantly.
Let me know what you think. Thanks