He forcibly picked into the back, the base of the bill and mostly into the back of the head of the dead mallard for about two minutes, then mounted the corpse and started to copulate, with great force, almost continuously picking the side of the head.
"Rather startled, I watched this scene from close quarters behind the window until 19.10 hours during which time (75 minutes) I made some photographs and the mallard almost continuously copulated his dead congener. He dismounted only twice, stayed near the dead duck and picked the neck and the side of the head before mounting again. The first break (at 18.29 hours) lasted three minutes and the second break (at 18.45 hours) lasted less than a minute. At 19.12 hours, I disturbed this cruel scene. The necrophilic mallard only reluctantly left his 'mate': when I had approached him to about five metres, he did not fly away but simply walked off a few metres, weakly uttering a series of two-note 'raeb-raeb' calls (the 'conversation-call' of Lorentz 1953). I secured the dead duck and left the museum at 19.25 hours. The mallard was still present at the site, calling 'raeb-raeb' and apparently looking for his victim (who, by then, was in the freezer)."