In May 2020, a brood of five Wrens Troglodytes troglodytes was raised in a nest inside an old Barn Swallow Hirundo rustica nest at Bramley, Hampshire. The Swallow’s nest was attached to the underside of the ridge beam, 4 m above the ground, within the apex of a doorless gable-roofed shed. On 20th May, when the chicks were about a week old, I noticed an adult Wren pecking at something on the ground below the nest. A close approach revealed that the bird was attacking a live Wood Mouse Apodemus sylvaticus. The mouse was very young and about 5 cm in length. My approach disturbed the Wren and I was able to pick up the mouse, which was shocked but seemingly unharmed. I released it, whereupon it ran away. Perhaps the Wren perceived the mouse as a potential predator or may have been attacking the mouse as a potential prey item: Wrens are known to take tadpoles, young frogs and small fish and their fry (Cramp 1988).