Sperm thermotaxis, the active orientation of sperm swimming according to a temperature gradient has been suggested to act as a long-range guidance mechanism in the oviduct during fertilization, between the cooler sperm storage site and the warmer fertilization site. In this process capacitated spermatozoa can sense even very shallow temperature gradients. They respond to the changing temperature by modulating their flagellar beating. The outcome is a higher frequency of turns and hyperactivation events when the temperature drops, and a rather linear swimming when they sense a temperature increase. In this way they are guided towards the warmer temperature.