Most of the Rock's upper area is covered by a nature reserve which is home to around 230 Barbary macaques, the famous "apes" of Gibraltar, which are actually monkeys. These are the only wild apes or monkeys found in Europe. This species, known scientifically as ''Macaca sylvanus'', is listed as endangered by the IUCN Red List and is declining. Three-quarters of the world population live in the Middle Atlas mountains of Morocco. Recent genetic studies and historical documents point to their presence on the Rock before its capture by the British, having possibly been introduced during the Islamic period. A superstition analogous to that of the ravens at the Tower of London states that if the apes ever leave, so will the British. In 1944, British Prime Minister Winston Churchill was so concerned about the dwindling population of apes that he sent a message to the Colonial Secretary requesting that something be done about the situation.