reported from two other sites in the nineteenth century, it currently grows only on two serpentine hills in the island of Unst. The nationally scarce oysterplant is found in several islands and the British Red Listed bryophyte Thamnobryum alopecurum has also been recorded. Listed marine algae include: Polysiphonia fibrillosa (Dillwyn) Sprengel and Polysiphonia atlantica Kapraun and J.Norris, Polysiphonia brodiaei (Dillwyn) Sprengel, Polysiphonia elongata (Hudson) Sprengel, Polysiphonia elongella, Harvey. The Shetland Monkeyflower is unique to Shetland and is a mutation of the Monkeyflower (mimulus guttatus) introduced to Shetland in the 19th century. Fauna Shetland has numerous seabird colonies. Birds found in the islands include Atlantic puffin, storm-petrel, red-throated diver, northern gannet and great skua (locally called "bonxie"). Numerous rarities have also been recorded including black-browed albatross and snow goose. A single pair of snowy owls bred in Fetlar from 1967 to 1975. The Shetland wren, Fair Isle wren, and Shetland starling are subspecies endemic to Shetland. There are also populations of various moorland birds such as curlew, lapwing, snipe and golden plover. One of the early ornithologists that wrote about the wealth of birdlife in Shetland was Edmund Selous (1857–1934) in his book The Bird Watcher in the Shetlands (1905). He wrote extensively about the gulls and terns, about the arctic skuas, the black guillemots and many other birds (and the seals) of the islands. The geographical isolation and recent glacial history of Shetland have resulted in a depleted mammalian fauna and the brown rat and house mouse are two of only three species of rodent present in the islands. The Shetland field mouse is the third and the archipelago's fourth endemic subspecies, of which there are three varieties in Yell, Foula, and Fair Isle. They are variants of Apodemus sylvaticus and archaeological evidence suggests that this species was present during the Middle Iron Age (around 200 BC to 400 CE). It is possible that Apodemus was introduced from Orkney where a population has existed since at the least the Bronze Age. Domesticated animals There is a variety of indigenous breeds, of which the diminutive Shetland pony is probably the best known, as well as being an important part of the Shetland farming tradition. The first written record of the pony was in 1603 in the Court Books of Shetland and, for its size, it is the strongest of all the horse breeds. Others are the Shetland Sheepdog or "Sheltie", the