Long-tailed tits help feeding young great tits

This May 2018 video was recorded in the garden of Evert Houniet in the Netherlands. It is about a great tit nest. The great tit chicks in the nestbox are fed not only by their parents, but also by two long-tailed tits.

Why? Biologists found that at out of eleven long-tailed tit nests, the parents were helped by other long-tailed tits in feeding the young. But this case, at a great tit nest, seems to be unique.

It is a bit surprising that the great tit parents are not aggressive towards the long-tailed tits. Great tits are often aggressive against other birds.

Sometimes, redstarts or blue tits or wrens help feeding young great tits. Blue tits may also help young marsh tits. And wrens may help blue tits.

Here is a video about a robin feeding a young blackbird.