It has been hypothesized (1) that the compass direction in which woodpeckers excavate breeding cavities depends on nest thermoregulatory needs, and (2) that when multiple cavities are placed in the same tree across years, each new cavity is placed above previous cavities. We tested these hypotheses for Red-naped Sapsuckers (Sphyrapicus nuchalis) in central Nevada and found some evidence that cavities are oriented for thermoregulatory advantage, but we rejected the hypothesis that active cavities are always the highest.
Butcher, Laurence R.; Fleury, Scott A.; and Reed, J. Michael
"Orientation and vertical distribution of Red-naped Sapsucker (Sphyrapicus nuchalis) nest cavities,"
Western North American Naturalist: Vol. 62
, Article 13.
Available at: http://scholarsarchive.byu.edu/wnan/vol62/iss3/13