Ard means Hieght or Highest or Exalted, Drewboy. Arden is the familiar of that name, like Thomas becomes Tommy when you familiarise it. It was probably used to show his exalted status amongst the druids rather than being his actual name. Or druids choose thier own names as they go through life to reflect their circumstances and feelings, and are renamed after certain initiatory experiences by their mentors. So you can have a birth name, a given name that might change at any time, and several chosen names. Ard is common in names as well as high places, anyhow.

This site has put all the Carmina Gadelic items relating to Bridget on one list if you want to look those up. http://www.ordbrighideach.org/home/modules.php?name=Encyclopedia&op=list_content&eid=1 The Carmina Gadelic itself is an interesting collection of pagan/christian merged beliefs and lore, the whole book is on sacred texts.com.

Tiompan, I recollect now about the pleiades... you were asking me my source of information. Now we have computer models they are doing more work on pleiadian alignments as the sky would have looked at different periods in prehistory, and coming up with good results. There's been some work done at Calanais for instance, and a google search on pleides stone alignements calanais or callanish will show up a few. http://adsabs.harvard.edu/full/1977JHA.....8..113C was the article I was reading about it, but forget the exact page. I'm sure the researcher that had done a lot of computer simulations of the ancient night sky was called Hawkes or Hawkins though.

I havent read this book, but the contents have pleiades connections in several chapters on a few other megalithic sites:
http://www.starsstonesscholars.com/tableofcontents.htm

I remember reading about those hazels which were being farmed on that island. The islanders left suddenly, but they burned down all 2000 hazel trees when they left, maybe rather than leave them behind for others that were causing them to move, maybe for other reasons. Lot of evidence of neolithic slash and burn methods on the mainland in Scotland too, huh. Happened long before the bible doctrine of man being in domination over all creation, and it being for mankind's use. Sometimes people in christian countries have a mistaken and somewhat parochial belief in its prevalence all over the world, though. Look at China. Or India.