“When the Norwegians came to Orkney and Shetland in the eighth and ninth centuries they brought with them their giants and trolls (trows as they became). Transplanted from Norway’s overwhelming natural background to somewhat low islands, the giants soon vanished, and the trolls diminished in size sufficiently to inhabit, along with hill-folk and hogboons, the mounds and tumuli conveniently left behind by prehistoric people.”
Ernest W. Marwick, The Folklore of Orkney and Shetland, published in 1975.
It's probably not related (neither is it much to do with folklore!), nevertheless interesting to read that the Norwegians "trolls became trows", because, down here in the West countree, specifically on the Rivers Severn and Wye, there was a traditional flat bottomed cargo sailing boat called a trow, whose masts could be taken down to pass under the bridges of larger towns. There's a pub in Bristol called the Llandogo Trow - named after the riverside village on the Wye where trows were once common. The pub is said to have inspired R L Stevenson's Admiral Benbow pub in Treasure Island - that's as close as I can get to a folklore connection!!