Photo courtesy of PaleMale.com -- 11/20/09
Bill Trankle, a faithful correspondent from Indianapolis, sent in the following note. Perhaps some reader has some more information on the subject:
Marie, as so often happens, I was struck by some of Lincoln Karim's photos of the great horned owl you New Yorkers were fortunate enough to have visiting last November; specifically I noticed for the first time that Le Grand Duc is zygodactylic (two toes on either side of a perch). Since hawks, falcons, eagles, and most raptors exhibit anisodactyly, with three toes forward and one back, I was wondering why some owls have evolved this configuration of toes. Wikipedia (http://en.wikipedia.org/wiki/Dactyly) indicates that zygodactyly is usually found in arboreal birds that clamber through foliage or climb tree trunks; while I've seen GHOs in the past, I've not gotten the chance to observe them in forested areas, so I don't know if that's typical behavior for these birds.