Dominica has been nicknamed the "Nature Island of the Caribbean" for its natural environment. It is the youngest island in the Lesser Antilles, and in fact it is still being formed by geothermal-volcanic activity, as evidenced by the world's second-largest hot spring, called Boiling Lake. The island has lush mountainous rainforests, and it is the home of many rare plants, animals, and bird species. There are xeric areas in some of the western coastal regions, but heavy rainfall occurs inland. The sisserou parrot, also known as the imperial amazon and found only on Dominica, is the island's national bird  and featured on the national flag, which is one of only two national flags containing the colour purple (the other being Nicaragua). The country is a member of the Commonwealth of Nations, the United Nations, the Organization of American States, the Organisation internationale de la Francophonie, and the Non-Aligned Movement.