A CLOSER LOOK—Hairy Woodpecker

by Kimball Garrett

Originally published in the Western Tanager Vol. 46 No. 8 May 1980.

Closer-Look-Woodpecker-illustration-by-Kimball-Garrett-scan 

Woodpeckers are at once unique and familiar, and there is ample opportunity in southern California to study some thirteen species in or near the region. Their suite of adaptations to scansorial (climbing) locomotion and bark and sub-bark foraging is so impressive, complex, and successful that creationists opposing a theory of evolution through natural selection have even used woodpeckers as an example of how far-fetched (in their minds) natural selection must be! This month, however, we will deal with only a few aspects of plumage variation in the Picoides woodpeckers, using the widespread Hairy Woodpecker as an example.

The Picoides woodpeckers are the familiar "pied" woodpeckers, represented in southern California by the Hairy, Downy, Nuttall's, Ladder-backed, and White-headed Woodpeckers. Formerly placed in the genus Dendrocopos, they were recently merged into the Three-toed Woodpecker genus Picoides to satisfy a growing trend in the genus concept which would stress similarities and common evolutionary ancestry within a family, rather than emphasizing differences between species.

It is well-known that male woodpeckers have more red on the head and face than female woodpeckers (in most cases), and often the males are the only adult sex to possess red markings. In North America, those species where males and females are essentially identical (e.g. Red-headed and Lewis' Woodpeckers) are a minority. At the other extreme, male and female Williamson's Sapsuckers are so different that for decades they were thought to be separate species! The red markings of the male certainly function in sex recognition; territorial males are likely to be quite intolerant of other woodpeckers bearing this red "flag," and the red may be displayed prominently in agonistic interactions. In the 1930s, G.K. Noble performed a series of experiments with the "Yellow-shafted" Flicker, a dimorphic from in which the males possess a black "moustache" and the females lack it. He found that a male will actually attack its mate if she has had a black "moustache"artificially painted on, indicating the importance of specific head markings to the general demeanor of a woodpecker!

In all of our Picoides woodpeckers, the males have a bright red nape (or occiput) patch, while adult females always lack such a patch (see Figure). In the Nuttall's and especially the Ladder-backed Woodpeckers, this red of the male extends onto the rear crown. Thus these species are all quite easily sexed in the field. Note that both males and females of these species may "drum" (roughly, the woodpecker equivalent of song), contrary to indications of some sources.

The Hairy Woodpecker typifies the Picoides woodpeckers in that adult females lack red. It also possesses a more complicated character typical of many species of the genus: The juveniles of both sexes have red on the head. Until the post-juvenile molt is completed sometime in fall, both male and female Hairy, White-headed, and other woodpeckers have red on the crown. These birds should not be mistaken for adult males; the red is generally of a paler hue than that of the adult male, and forms a patch on the crown, rather than on the occiput. In addition, juveniles early in the fall tend to have noticeably shorter bills than the adults, and a "softer" appearing plumage. At least in the White-headed Woodpecker, juvenile males tend to have more red than juvenile females. The social implications of the presence of red on juvenile female woodpeckers are not entirely clear. Juvenile Picoides woodpeckers usually associate closely with their parents for at least a few weeks after fledging, so the red doesn't seem to operate as a "weaning" mechanism (by provoking attacks by the male parent).

The Hairy Woodpecker also shows some geographical (racial) variation in southern California. The widespread breeding race (in the mountains, foothill canyons, and very locally in the lowlands) is P. villosus hyloscopus. From the White Mountains south (at least formerly) to Clark Mountain on the eastern Mohave Desert, the race P. v. leucothorectis occurs. It is somewhat larger and much whiter below than hyloscopus, but these differences are not obvious in the field. In the Pacific Northwest, Hairy Woodpeckers are dingy gray below; at the southern end of their range (in Central America south to Panama) they are nearly as small as a Downy Woodpecker and uniform brown below.

By June and July, woodpecker young of many species should be fledged, giving the observer the opportunity to see red, studying its extent in the juveniles of the various species, and perhaps elucidating some of the behavioral implications of this unusual plumage development.


 

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