Great tit infanticide?

I have a camera in a bird box being used by great tits. The laid 7 eggs and all 7 hatched. Unfortunately one of the chicks died after nearly a week and its body was removed early in the morning. Just before midday one of the parents kept pecking at the rear of one of the chicks pulling it around by the tail stump with the chick struggling. This lasted for a couple of minutes before the parent was able to get the chick, still alive although now weakend into a position where it could get a good grasp on the tail stump and left the nest box. Is it usual for still live chicks to be removed from the nest? The chick put up a struggle so it did not seem obviously sickly.

  • Second chick attacked by parent after incubating for a while and thrown out of nest bowl, but still in nest box. Struggled back to nest bowl after parent left and was fed and brooded later. Another or the same chick had its rear end attacked the next day and was thrown out of the nest bowl but still in box. This time the chick succumbed and its body was left at side of nest bowl.