Rivers region has a monsoon climate. The dry season lasts between May and September while the wet season lasts between November and March. April and October are transitional periods between the two seasons. Annual rainfall at Jabiru is around , with almost all of it falling during the wet season. During the wet season, the prevailing winds are westerly to northwesterly, while they are easterly to southeasterly during the dry season. The three Alligator Rivers are perennial rivers flowing even during the dry season, as is the Wildman River. All of the tributaries dry up in places during that period. The land dries out, and the wildlife concentrates around the permanent water sources such as the rivers, springs, waterholes, and billabongs. The duration of the dry period depends on the rainfall during the wet season. In a normal year, the tributaries start flowing around the middle of December and finish at the end of June, but the flow starts in November and finishes in August if the rainfall has been particularly heavy. During the wet season, the savanna turns green, the wildlife spreads out, the bird life returns, and the streams flood into adjacent lands turning them into swamps. The flood plains leave behind silt when they gradually dry up during the wet season. During the wet season, the water has a higher temperature and is relatively low in turbidity. In the dry season, an increase in turbidity occurs, especially in the shallower water sources. The Alligator Rivers region is also subject to cyclones between October and May, like other parts of the Australian Indian Southeast region. Wildlife The region takes its name from the crocodiles in the lower reaches of the rivers. However, the region features a wide diversity of plant and animal habitats. More than 1,500 species of plants have been recorded in a range of tropical habitats including mangrove, monsoon forest, tropical grassland, and woodland. The 46 species of fish in the river system represent about a quarter of all known species existing in Australia. The region also features high populations of the dusky rat and its predator the water python. New vertebrate species are still being discovered in the region, notably the Kakadu dunnart and the Kakadu Pebble-mound Mouse. The potential for discovery of invertebrate species, such as ants is even greater. Some threat to the ecosystems exists from introduced flora and fauna. Introduced species of