Swallowtail, Swallow Tail, Swallow's Tail

Which is correct - Swallowtail, Swallow Tail, Swallow's Tail?  I guess it depends on what time frame you consider.

Early on, the peninsula was called Swallow's Tail, referring to the shape of the peninsula in relationship to the coves flanking it on either side.  The peninsula looked like the long tail of a swallow, birds that were plentiful on the island, but unfortunately today are getting more and more difficult to find.

Illustration of a swallow superimposed on the peninsula to show the similarities.  The curve of Pettes Cove, called Sprague's Cove in the 1850s, closely mimics the curve of a swallow's wing.

From the NB Lighthouse Publishing article Swallowtail Lightstation History. Update Posted 03.03.2007:

In a Dec. 15th, 1859 report I. Woodward of the Commission of Lighthouses said (p. 317 Board of Public Works Appendix, April 1860):


Sir, I have to report that in accordance with your request to me in the month of June last that I would proceed to Grand Manan taking with me John P. McKay and select a site for a lighthouse at the "Swallow's Tail" which he had contracted to build. We left Saint John on the 27th of June by steamer from Eastport, where, joined by Captain Robinson, R.N.Commissioner of Lighthouses, we proceeded to Grand Manan, whereon the 28th and 29th, we selected a spot on the Point known as the "Swallow's Tail", for the contemplated lighthouse and keepers house. Made an arrangement with the owner of the land, Mr. James Small, residing at Sprague's Cove...   The apostrophe "s" was dropped at some point and became Swallow Tail, only to be further modified to Swallowtail.  We have opted for the Swallow Tail spelling in our recent work but Swallowtail is still used extensively.