Pileated double-knocks

This information is from an anonymous source:

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The Pileated Woodpecker does give a double-knock. This behavior has been known for many years; for example, here's a snippet from Short's 1982 monograph (p. 419) regarding "demonstration tapping" in the Pileated [my comments in brackets]:

"This form may occur as a double tap, akin to the drum taps that are characteristic of various species of Campephilus; such a double tap may be associated with copulation or may occur at a prospective nest site (Kilham, 1959d, p. 381). Such demonstration tapping is known in D. javensis and D. martius [a reference to the congeneric White-bellied and Black Woodpeckers]. Drumming takes place all year, but especially marks the prebreeding period, for example, in December and January [when CLO's ARU cuts were obtained] in Maryland (Kilham, 1959d). Bent (1939, p. 175) cites Sutton as indicating that a drumming burst may be followed by three distinct blows, thus resembling drum taps of Campephilus, but Hoyt (1957) did not thi[nk] these are typical, nor do I."

Cornell has a Pileated Woodpecker recording that is a clear double knock, indistinguishable to expert ears from a Campephilus. Nothing in the ARU cuts eliminates PIWO or, for that matter, a Red-bellied Woodpecker or Yellow-bellied Sapsucker, both of which "double knock" as well.
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Again, if you collect 17,000 hours of audio data in an area containing Pileateds but no Ivory-bills, you should expect to hear a lot of double-raps.

Here's a previous post on the topic.