the island is subject to long periods of drought. Historical droughts on Niihau have been recorded several times, one in 1792 by Captain James Cook's former junior officer, George Vancouver, who had been told that the people of Niihau had abandoned the island because of a severe drought and had moved to Kauai to escape famine. Flora and fauna As an arid island, Niihau was barren of trees for centuries – Captain James Cook reported it treeless in 1778. Aubrey Robinson, grandfather of current owners Bruce Robinson and Keith Robinson, planted 10,000 trees per year during much of his ownership of the island; Robinson's afforestation efforts increased rainfall in the dry climate. Island co-owner Keith Robinson, a noted conservationist, preserved and documented many of Niihau's natural plant resources. The island is designated as a critical habitat for the ōlulu, an endemic and endangered species of Hawaiian lobelioid. Pritchardia aylmer-robinsonii, a palm tree named for Keith Robinson's uncle Aylmer Robinson, is an endangered species native to Niihau. Several bird species thrive on Niʻihau. The largest lakes on the island are Hālaliʻi Lake, Halulu Lake and Nonopapa Lake. These intermittent playa lakes on the island provide wetland habitats for the ʻalae keʻokeʻo (Hawaiian coot), the āeʻo (Hawaiian subspecies of Black-necked Stilt), and the koloa maoli (Hawaiian duck). The critically endangered Hawaiian monk seal (Monachus schauinslandi) is found in high numbers on Niʻihau's shores. Robinson states that Niʻihau's secluded shoreline offers them a safe haven from habitat encroachments. According to Robinson, conditions there are better than the government refuges of the Northwestern Hawaiian Islands. When the Robinsons originally purchased Niʻihau, no monk seals were present, because they lived in the northwestern part of the Hawaiian island chain, Necker and Midway islands. They have been relocated to the main Hawaiian island chain by NOAA fisheries over the past thirty years, and some have found homes on Niʻihau. Big game herds, imported from stock on Molokai Ranch in recent years, roam Niihau's forests and flatlands. Eland and aoudad are abundant, along with oryxes, wild boars and feral sheep. These big game herds provide income from hunting safari tourism. History Prior to the unification of the Kingdom of Hawaii under Kamehameha I, Niihau was ruled by the . Kahelelani was the first of the Niihau alii. His name is now used to refer to the Niihau kahelelani, the puka shell of the wart turbans (Leptothyra verruca),