Kemerton Conservation Trust

The Use of Mirrors to Deter Nest Box Predators By John Clarke, December 2002

On a local estate we run a nest box scheme and many of the 150 boxes attract small, hole-nesting birds such as Tits. Damage and/or predation by Great Spotted Woodpecker is fairly common but in some plantations became so bad that boxes were damaged within days of being put up. In two sites the problem forced us to abandon attempts to provide artificial nest sites.

Some years ago I was waiting for a farmer outside his house in Herefordshire when I noticed a colony of House Martins. There were about thirty nests under the eaves of the house but most strikingly, just below each one there was a small piece of mirror. The farmer explained that he had once reared an orphaned Great Spotted Woodpecker in a budgerigar cage.

As the bird grew he provided a perch, then a ladder and then a bell – all of which the young bird accepted. However, when he hung a mirror in there the woodpecker went berserk apparently terrified by its own reflection. The farmer had problems with GSW predating his House Martins nests and so stuck pieces of mirror below each one. The effect was instant, and from then on he had no further instances of nest damage.

Great Spotted Woodpecker

I fixed small mirrors to 14 nest boxes, siting 12 in 3 plantations where the worse damage (usually 100%) had occurred. The other two were sited in gardens. After six months one plantation box and one garden box had been damaged. After eighteen months a further two boxes had been damaged in a second plantation. At least 10 of the nest boxes had been occupied by tit spp.

To summarise, Mirror Boxes in one plantation were 100% effective, in the second plantation 75% survived for 18 months; and in the third 50% survived for 18 months. Two of the four damaged boxes were accessed via the side and not by enlarging the entrance hole.

So, mirrors clearly deter GSW from attacking nest boxes. I doubt if the idea will catch on but it does provide an interesting insight into bird behaviour.