The use of mirrors to deter nest box predators

Published source details Clarke J. (2002) The use of mirrors to deter nest box predators. Kemerton Conservation Trust report, Surveys and Research website article: Nest box protection trial.
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Summary

On the Kemerton Estate in Worcestershire, southwest England, a nest box scheme is operated. Many of the 150 nest boxes attract small, hole-nesting birds such as tits Parus spp. Damage and/or predation of eggs and young by great spotted woodpecker Dendrocopos major was observed to be fairly common but in some plantations became so bad that boxes were damaged (e.g. the entrance hole enlarged) within a few days of being installed. At two sites the problem forced abandonment of attempts to provide nest boxes. Observations of a young captive great spotted woodpecker by a local farmer indicated that it appeared very intimidated when it saw its reflection in a small mirror installed in it's cage. This in turn led to the idea of fixing mirrors to the exterior of nest boxes in an attempt to deter woodpeckers, thus reducing damage and nest predation. This study summarises the deterent effect of attaching mirrors to a selection of nest boxes.

Study site: The effect of adding small mirrors to nest boxes in an attempt to reduce great spotted woodpecker damage and predation was undertaken on the 465 hectare Kemerton Estate (owned by the Darby Family) near Tewkesbury, south Worcestershire. Through the creation of nature reserves and the efforts of the farm mangers to increase biodiversity, a wide range of habitats have been maintained and improved.

Nest box mirrors: A small mirror was fixed externally to the front of 14 wooden nest boxes, 12 in three plantations where the worse damage to nest boxes (usually 100%) had occurred, and two in gardens.

Monitoring: The boxes were monitored over a period of 18 months to record woodpecker damage and use by nesting passerine birds.

Nest box damage: After six months one plantation box and one garden box had been damaged by woodpeckers. After eighteen months a further two boxes had been damaged in a second plantation. Mirror boxes in in one plantation were 100% effective (no damage up to 18 months); in the second plantation 75% had no damage after 18 months; and in the third 50% had no damage for 18 months, as compared to almost all boxes being damaged prior to mirror attachment. Two of the four damaged boxes were accessed via the side and not by enlarging the entrance hole.

Nest box occupancy: At least 10 of the 14 nest boxes were occupied by tit spp. and young successfully reared over the duration of the 18 month monitoring period.

Conclusions: In this small trial, attachment of small mirrors to the exterior of nest boxes appeared to deter great spotted woodpeckers from damaging wooden nest boxes on the Kemerton Estate.

Note: If using or referring to this published study, please read and quote the original article, this can be viewed at: http://www.kemerton.org/Nest%20Box%20Trials.htm