Another behavious system is the 'dances' of water birds such as the Great Crested Grebe. They pair for life, and 'dance' whenever a pair meet up after an absence, and on other occasions. The dances are quite complex, and were first described fully by Julian Huxley. Here the meeting is the releaser, and both partners do the fixed action pattern. The function of the system is a little unclear, but it has something to do with reinforcing the pair's bond.