A gowan is a daisy. Kent (or kenned) is the past tense of ken, to know; now mostly used only in Scotland and the North of England. Blythe is the once common, though nowadays a little old-fashioned, word blithe (happy, cheerful).

A cushat is a (wood) pigeon. Burnie, I'd guess, is in this context a diminutive form of burn, a small stream or brook.

Don't know about porteth, mind.