Hello UXOEOD,
This has been an often and long debated topic in the ornithological communities and not a modern one. It becomes more discussed in modern times as a product of technology.......and probably shrinking public space. The best way to describe the debate and issue is in terms of agenda and personal convictions. The agendas are varied when we step out into the natural areas and shared space tends to drive much of the debate than stress on the bird. To date, there has been no definitive study that confirms, one way or another, that call backs place undue stress on a bird. My personal take on it sits with how the call back is used versus using it. In the case of woodpeckers, your sapsucker being one of them, tapping is a form of call back. Woodpeckers do not sing like other birds but rather use tapping to attract mates and set territorial boundaries. Where warblers, sparrows, etc. sing, woodpeckers tap. They have different volumes and cadence that communicate different purposes. As a visitor to the forests and marshes/swamps, we will also here tapping as they drill for food. But the tapping for food is different than the territorial tapping.
As mentioned, this debate, surrounded by agendas, has been around for a long time. John Burroughs, the turn of the century naturalist, wrote about the aspects of different agendas between science, artists, recreational birds and others just after the turn of the century. He reconciled it by noting all have a love for thing, though the agendas often cross in conflict. It is an interesting perspective on the issue as I am sure that birder that criticized you has a love for thing as you do. So, this judgement of behavior, as used to fit agenda, has been around for a while. What is ethical? Only can only determine that for yourself, personally I do not see what you did as being unethical. But from another's perspective they might. But always keep in mind, just our presence is a disturbance, so argument could be made that the birder's presence, and yours, and mine when out and about, is disturbing a pure context of ethics.
Also keep in mind that many biologist use call backs and decoys to attract and catch birds for research. American Oystercatcher are usually caught in whoosh nets placed inside a birds territory with a decoy and call back. Same with Willets. Warbler researchers use mist nests, decoys and call backs to catch and tag warblers. The list is very long. One thing about the argument of using a call back that is often missed is that it can be less intrusive if used properly. It targets a single species, leaving others undisturbed. Unlike the technique of phishing that can unnerve many different species, a call back does not. The other is that it may affect other users of the area, like a birder, who often notes identification by song......or in this case tapping. I know birders in my area that can identify the woodpecker by the cadence of the territorial tapping..........it is a skill I do not have, and probably a skill only the top birders develop.
This debate was addressed by David Sibley. For those who do not know David, he is one of the foremost bird authorities and authors known today, and well respected. I attached a link to what he says about it:
http://www.sibleyguides.com/2011/04/the-proper-use-of-playback-in-birding/Some species require playback. Anyone that has worked with Black Rails will quickly tell you that without a playback it would be difficult to near impossible to determine presence, population, habitat use and range.
It is also worth noting that most of the major ornithologist and naturalist, from Alexander Wilson, Baird, Audubon up to modern times, used or use they same technique you used. Only difference is that today, we do not collect the specimen as early ornithologists and naturalist would.
I have seen people drag ropes a across fields to flush sparrows, trudge through protected areas to see a bird, and just about every other type of extreme behavior (or unethical behavior) in pursuit of their agenda........which includes birders, photographers, researchers, etc. I have also seen a lot of the same not using extreme behavior. People will act differently as dictated by their agenda........and some way out of bounds. But, my experiences generally support that the majority of people, regardless of agenda, tend to keep themselves with boundaries of behavior. I do not think tapping on tree is outside boundaries. I just think the birder you met that day has a much more narrower defined boundary and prefers others to be defined by that boundary versus expecting another's.
As to your sapsucker. One thing about that bird is that it will drill a series of horizontal holes in trees for the sap. It will return regularly to these same holes. If you find a sapsucker holding in a territory, which is probable as breeding season begins, and you find a nice tree that has those holes (they are obvious, it drills many), then you could stake out that tree and wait for it to return and get yourself a really nice photo. Best to get there and wait for the bird........I have used this approach many times with sapsuckers.
Good luck with your shooting............and no, I do not think you did anything to worry about nor anything that the greatest past and present ornithologists and naturalist would do.