Nest tree characteristics of the old-growth specialist Three-toed Woodpecker Picoides tridactylus

Abstract

The Three-toed Woodpecker Picoides tridactylus is a mature and old-growth forest specialist but how the species uses trees for nesting in its breeding sites and whether cavity trees are a critical habitat feature is poorly known. We studied the nest tree characteristics of the species in a 170-km2 area in southern Finland during 1987–2016. The data included 538 nest trees of eight different species and 665 nest cavities in 86 territory areas. Norway spruce Picea abies was the predominant nest tree comprising 71% of all nest trees. Proportionally, deciduous nest trees were more common in moist forests on mineral soils and conifer nest trees more common in spruce swamps. The majority of nest trees (85%) were dead or decaying trees; higher numbers of dead deciduous nest trees were recorded than dead conifer trees. The mean diameter of a nest tree at diameter at breast height (DBH) was 29.4 cm and the mean height of a cavity hole was 5.1 m; size and height were significantly positively correlated. The proportion of deciduous nest trees was significantly higher (45%) in natural forests compared with other areas subjected to variable amounts of forest management, where the respective proportion was only 9–17%.