There are two parts to a roof, its supporting structure and its outer skin, or uppermost weatherproof layer. In a minority of buildings, the outer layer is also a self-supporting structure.
The roof structure is generally supported upon walls, although some building styles, for example, geodesic and A-frame, blur the distinction between wall and roof.
When the Dutch arrived in the area in 1652, the only large animals on the island were seals and birds, principally penguins. In 1654, the settlers released rabbits on the island to provide a ready source of meat for passing ships.
The original colony of African penguins on the island was completely exterminated by 1800. However the modern day island is once again an important breeding area for the species after a new colony established itself there in 1983. The colony grew to a size of ~16,000 individuals in 2004, before starting to decline in size again. As of 2015, this decline has been continuous (to a colony size of ~3,000 individuals) and mirrors that found at almost all other African penguin colonies. Its causes are still largely unclear and likely to vary between colonies, but at Robben Island are probably related to a diminishing of the food supply (sardines and anchovies) through competition by fisheries. The penguins are easy to see close up in their natural habitat and are therefore a popular tourist attraction.
Around 1958, Lieutenant Peter Klerck, a naval officer serving on the island, introduced various animals. The following extract of an article, written by Michael Klerck who lived on the island from an early age, describes the fauna life there:
My father, a naval officer at the time, with the sanction of Doctor Hey, director of Nature Conservation, turned an area into a nature reserve. A 'Noah's Ark' berthed in the harbour sometime in 1958. They stocked the island with tortoise, duck, geese, buck (which included Springbok, Eland, Steenbok, Bontebok and Fallow Deer), Ostrich and a few Wildebeest which did not last long. All except the fallow deer are indigenous to the Cape. Many animals are still there including three species of tortoisethe most recently discovered in 1998two Parrot Beaked specimens that have remained undetected until now. The leopard or mountain tortoises might have suspected the past terror; perhaps they had no intention of being a part of a future infamy, but they often attempted the swim back to the mainland (they are the only species in the world that can swim). Boats would lift them out of the sea in Table Bay and return them to us. None of the original 12 shipped over remain, and in 1995, four more were introducedthey seem to have more easily accepted their home as they are still residents. One resident brought across a large leopard tortoise discovered in a friend's garden in Newlands, Cape Town. He lived in our garden and grew big enough to climb over the wall and roam the island much like the sheep in Van Riebeeck's time. As children we were able to ride his great frame comfortably, as did some grown men. The buck and ostriches seemed equally happy and the ducks and Egyptian Geese were assigned a home in the old quarry, which had, some three hundred years before, supplied the dressed stone for the foundations of the Castle; at the time of my residence it bristled with fish. Recent reports in Cape Town newspapers show that a lack of upkeep, a lack of culling, and the proliferation of rabbits on the island has led to the total devastation of the wildlife; there remains today almost none of the animals my father brought over all those years ago; the rabbits themselves have laid the island waste, stripping it of almost all ground vegetation. It looks almost like a desert. A reporter from the broadcasting corporation told me recently that they found the carcass of the last Bontebok.
There may be 25,000 rabbits on the island. Humans are hunting and culling the rabbits to reduce their number.