By Barbara Johnson
We have two nest-boxes, one either side of our garden. One with a smaller hole, just for blue tits, the other with a larger hole to accommodate great tits, sparrows etc.
One year a pair of blue tits successfully reared a brood in the ‘great tit’ box and from very early the following spring kept watch over the box, warding off any birds that showed an interest in it. Eventually we saw moss etc being taken into the box as the pair prepared to nest there again.
Then one afternoon we heard a terrible commotion in the garden and saw two very agitated blue tits at the entrance of the nest box and a great tit watching from a few feet away.
One of the blue tits suddenly entered the box and after hearing a brief skirmish the blue tit emerged pulling a great tit by the wing, which it then somehow managed to drag out of the box.
The great tits beat a hasty retreat and the blue tits went on to successfully rear another brood.
great tit 
blue tit
Photographs: CC0
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Lovely story. Thank you Barbara.
Great tits are much bigger than blue tits, That must have been quite a struggle.
Yes it was, perhaps the Great tit backed down as he knew the Blue tit already had possesion, and the Blue tit was VERY upset!
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There are other nest boxes around the garden too.
Blue tits are very territorial and, for such a little bird, very fierce.