The most spectacular feature of the Magnificent frigatebird is of course its red gular sac. It can be filled with air to attract females during the mating season - a procedure that takes around half-an-hour and that makes it impossible for the bird to fish or even to eat. Therefore, it is filled only when the bird is ready to mate. The male to the left is obviously prepared to attract a female, while the male to the right has emptied his gular sac.