The role of woodpeckers (family: Picidae) as ecosystem engineers in urban parks: a case study in the city of Madrid (Spain)

Many species of the family Picidae, such as the woodpeckers, excavate the tree-cavities where they nest. Frequently the cavities are used during a single breeding season and subsequently abandoned, which allows their use by non-excavator species for nesting or roosting. Here we analyze the role of woodpeckers as providers of nesting and refuge places in two urban parks in the city of Madrid. The environmental characteristics of the woodpecker nest-sites were also studied. Prior to the breeding season 75 trees bearing woodpecker-excavated cavities and 142 control trees (i.e. without woodpecker cavities) were located, georeferenced and characterized by a set of variables relative to the tree and its environment. During the breeding season the cavities were monitored with an endoscopic camera to verify occupation and user identity. Additionally, 71 non-excavated tree-cavities were monitored to measure their occupancy and make comparisons with those excavated by woodpeckers. Woodpeckers showed a strong preference for trees of the genus Populus: 54 of 75 (72%) woodpecker-cavities were in poplars, which comprised only 7–10% of available trees. The excavated cavities were found mainly in the trunk of the trees, north oriented and away from paths. The occupancy rate by bird species was higher, although not significantly, for excavated cavities than for natural cavities (36.0% and 23.9% respectively). The richness and composition of cavity-user species also differed between types of tree-cavities. This work shows the importance of woodpeckers as providers of nesting and refuge places for other cavity-user birds and highlights their role as ecosystem engineers in urban parks. Finally, we consider that these results can guide biodiversity conservation efforts in urban planning.