Identifying tree attributes selected for foraging by Magellanic woodpeckers (Campephilus magellanicus) in the Cape Horn Biosphere Reserve

Background/Question/Methods

Understanding how woodpeckers select foraging trees is critical for the conservation of endangered woodpecker species, such as the largest South American woodpecker: Campephilus magellanicus. We assessed selection of individual trees of lenga (Nothofagus pumilio), coigüe (Nothofagus betuloides), ñirre (Nothofagus antarctica) and canelo (Drimys winteri) trees by Magellanic woodpeckers in a sub-Antarctic forest mosaic on Navarino Island. During the 2012 post-breeding season (austral summer) we used radio-telemetry to track six male woodpeckers, totalizing more than 600 records. Using focal sampling data and resource selection functions we compared the attributes of trees used by these woodpeckers and available trees that were randomly chosen within foraging plots. The tree attributes were species, height, diameter, decay state, position, and presence of woodpeckers pecking marks. Decay state was measured as the dead proportion of the tree, and position was the angle relative to the ground.

Results/Conclusions

Our results show that the diameter, decay state, and presence of pecking signs on a tree have a positive effect on the probability of a woodpecker in selecting a tree, whereas the tree age and height have no significant effect. These results suggest that not only the size and health of a tree are important cues used by Magellanic woodpeckers for tree selection, but also its previous use as a foraging substrate. These result shows that woodpeckers are not selecting the trees randomly, but seems that birds have a good understanding of resource distribution at a fine spatial scale. However, the mechanism is still not understood.

Acknowledgements: Funding was provided by University of North Texas, Universidad de Santiago, Universidad de Magallanes and Institute of Ecology and Biodiversity.