I recorded this today in the northern sector.
The first sound is Frank Wiley’s double knock with cypress dowels on a tree. The response comes approximately nine seconds later. There was no human activity in the vicinity at the time, and the spectrogram makes it clear that the source is natural. The intra-knock interval appears close to what would be expected for a large Campephilus woodpecker, approximately .11 seconds.
This was at a site where we’ve now got two cameras deployed. Frank will be posting a discussion of the pros and cons of game cams in the near future.
Edited to provide more context: I should have included this potentially significant detail – prior to my turning on the camera, Frank Wiley heard an ambient single knock that I missed. This was followed by agitated calling from a Pileated Woodpecker, Barred Owl vocalizations, and scolding from several Red-headed Woodpeckers, all of which I heard. The single knock gave him the impetus to do a single ADK. Thus, the circumstances were somewhat different from the typical use of ADKs as an attempt to attract or generate a response.
On further edit 12/31: I’ve modified the title from “. . .Apparent Double Knock in Response” to “Apparent Double Knock in Apparent Response” to correct the logical fallacy in the previous headline.