People believe that British sealer Peter Kemp was the first person to discover the islands on 27 November 1833, but we cannot be sure. On 25 November 1853, American sealer John Heard definitely saw Heard Island, and had it named after himself. A few months later, in January 1854, Briton William McDonald discovered the McDonald Islands. These two islands are external territory of Australia - they consist of the main volcanic island Heard, the Shag Islands lying 11 km north, and the three McDonald Islands (Flat Island, McDonald Island, and Meyer Rock) 43 km west. Heard Island covers 390 sq km and about 20% of it is unglaciated. Big Ben, the circular volcano of which the island is made of, is still active - it erupted in 1910, 1950, 1985 and 1992. The highest point on the island is Mawson Peak, which rises 2745 m above sea level - it is much higher than any other mountain in Australia. The Heard and McDonald Islands are the only sub-Antarctic islands without any feral species. Because of this, anyone going ashore must wear thoroughly clean footwear and clothing. The islands house the Heard Shag, as well as more than 2 million Macaroni Penguins and more than 200, 000 King Penguins (which are rapidly increasing).