The effect of tree hardness on woodpecker nest entrance orientation

Publication Type:

Journal Article

Authors:

Conner, Richard N.

Source:

Auk, Central Ornithology Publication Offic, Volume 94, Issue 2, p.369-370 (1977)

Call Number:

A77CON01IDUS

URL:

https://sora.unm.edu/node/22983

Keywords:

Colaptes auratus, Common Flicker, Downy Woodpecker, Dryocopus pileatus, Hairy Woodpecker, Picoides pubescens, Picoides villosus, Pileated Woodpecker

Abstract:

Previous work has indicated that woodpeckers in southwestern Virginia orient the entrances to their nest cavities in a slightly downward direction and predominantly toward the east-northeast. Blume, Lawrence, and Dennis have suggested that moisture on the underside of a sloping trunk might favor fungus growth that would soften the sapwood and make excavation through that side of the tree easier. As the woodpeckers in southwestern Virginia typically select trees with heart rots for nest sites, once they have excavated through the sapwood, excavation of the rotted heartwood of the nest tree is usually easy. The present study was designed to determine if the hardness of the sapwood of woodpecker nest trees has an effect on determining woodpecker nest entrance orientation in southwestern Virginia. During the summers of 1974 and 1975 I measured the hardness of the sapwood portion around the outsides of the nest cavities of Common Flickers (Colaptes auratus) (10 nests), Pileated Woodpeckers (Dryocopus pileatus) (10 nests), Hairy Woodpeckers (Picoides villosus) (8 nests), and Downy Woodpeckers (P. pubescens) (9 nests) on the Jefferson National Forest near Blacksburg, Virginia. As my data do not indicate that the woodpeckers selected the hardest or the softest side of the tree for nest entrances, the hardness of the sapwood of the nest tree apparently has little or no effect on the orientation of the nest entrance. My results should not be misinterpreted to say that woodpeckers do not select for hardness at all. Over 70% of the nest cavities that I examined had firm sapwood around the entire cavity. Excavation of nest cavities in trees with firm sapwood surrounding the entire cavity would probably have a selective value in being a predator deterrent. In conclusion, I suggest, as before, that the slight downward orientation of woodpecker nest entrances in southwestern Virginia has a selective value in that the nests are easier to defend against predators and competitors, and that they are less likely to fill with rain water.