Western Kenya is not just the Mara. It is also Lake Victoria and its surrounding environs, Kakamega Forest, Mt Elgon, Saiwa Swamp and Ruma National Park. However, for the purposes of understanding the effects of climate on the behaviour of animals, we will be speaking mainly of the Mara Triangle, which is situated in the Trans Mara District in south-west Kenya, along the Kenyan-Tanzanian border.
The migration is a weather driven phenomenon. A damp, plains habitat, the Mara Triangle is watered by the Mara River and its tributary, the Talek River. An elevation of between 1500 and 2180m, an average annual daytime temperature range of 21°C and 26°C and an average annual rainfall of 1400mm. The pattern of precipitation is classically bimodal, with the long rains March to the end of May and the short rains October to December. In this respect, the Mara differs from much of the rest of western Kenya which, under the influence of Lake Victoria and possibly the Congo airstream, experiences a single rainy season - from March to September.
Depending on the rains, the migration can arrive in the Mara any time between July and early September, taking advantage of standing water and fresh grass supplies. It will remain for the duration of the short rains, before moving south in November. The area boasts healthy numbers of resident populations, all which are best viewed in the dry season - January to March and June to September.