Black Woodpecker (Dryocopus martius) Foraging Behavior: More Support for an IBWO Diagnostic?Posted: January 22, 2015
I’ll be returning to Louisiana in late February and hope to make a couple of more trips during peak search season. Frank has retrieved the cards from our game cams and is in the process of going through several weeks of images. In contrast to the last set, there have been no intriguing hits thus far.
Last month, I came across a very interesting post on the Woodpeckers of the World Facebook group. The link took me to a French website that features some videos of the Black Woodpecker (Dryocopus martius), a Eurasian species, and one of the largest woodpeckers in the world, surpassing the Magellanic in size. In another analogy to the Magellanic, the Black Woodpecker appears to have certain features that are more Campephilus-like than others in genus Dryocopus. This includes flight style; acording to Gerard Gorman’s monograph on the species, Black Woodpeckers don’t generally undulate in flight. More importantly, the size and appearance of the bill certainly evoke the IBWO – generally larger, thicker, and heavier than a Pileated’s. Bill length can reach over 70 mm (although the average is 53-56 mm). According to Tanner, the mean length for ivorybills ranged from 67.8 mm to 74.1 mm depending on sex and region.
For my purposes, this is the most interesting clip. It’s an outstanding sequence that shows a Black Woodpecker scaling bark from a medium-sized hardwood branch. I see the following aspects as being significant and supportive of the hypothesis on feeding sign I’ve discussed in several posts, including here, here, here, here, and here.
For the most part, the bird is removing bark with direct strikes, not the lateral blows of a Campephilus woodpecker. This is possible because the limb is relatively thin, and the bird is able to position herself so that direct strikes will have the same effect that a more lateral blow would have on the bole; she generally engages in lateral movements to flick away bark after it has been loosened. The clip also seems significant insofar as it reveals the amount of effort involved to remove large but very thin strips of bark. In addition, even though the bark is thin, it seems the bird is still removing it in layers, at least some of the time. I think the video tends to support my idea that the work we think is diagnostic – on boles with thick tight bark – is beyond what PIWOs can do physically. At the same time, the footage suggests that the high branch work that Tanner emphasized is likely within the capacity of a Pileated Woodpecker and is indeterminate as we suspect.
In looking at images of Black Woodpecker foraging sign online, it appears that – bill structure notwithstanding – they typically remove bark in layers, just as Pileated Woodpeckers do, and this is true on both hardwoods and softwoods. I have been unable to find any examples of Black Woodpecker work that closely resemble what we think is diagnostic for ivorybill, but examples of the layered scaling are easy to find, for example: