Thorny forest of Whistling Thorn Acacia (Acacia drepanolobium) in Aitong province of Kenya, just north of the Masai Mara Game Reserve. A strong wind produces a continuous whistling sound passing over these branches. The dark swellings, or domatia, on the branches are hollow homes for ants (Crematogaster sp.) which participate in a mutualistic symbiosis with the trees, protecting them from herbivores.