Does canopy pruning affect foliage-gleaning birds in managed cork oak woodlands?

Semi-natural cork oak woodlands are a biodiversity rich agro-silvo-pastoral system covering large areas in the Mediterranean. Canopies of adult oaks are often pruned, but nothing is known about the consequences of this treatment on biodiversity. We evaluated the impact of pruning on birds that forage in cork oak canopies in an area of southern Portugal. We characterized the use of trees by foraging birds with focal observations, and analysed the effects of pruning on density with point counts on pruned and control areas. As pruning reduces the foraging substrate for foliage gleaners, we predicted that these species would have lower densities in pruned areas. Pruning did not substantially affect overall bird density or species richness. However, as predicted, the density of species that foraged mostly by gleaning in the canopy tended to be lower in pruned areas, especially in winter when differences were statistically significant. In this season the combined density of foliage gleaners in the pruned stations was only half of that in controls. Pruning is also common in other managed Mediterranean woodlands that are important for birds, such as holm oak woodlands and olive groves, and foliage gleaners are likely to be affected in those too. The cumulative effects of pruning on all these habitats need to be assessed, but our results already indicate that pruning has negative consequences that should be properly considered in management decisions.