they will fall from the nest. The adults feed their offspring for around 13 weeks, right up until the time they leave. The young birds fledge between 84 and 97 days old, departing by launching themselves off a cliff and flying—a procedure for which it is impossible to practice beforehand. If they leave the nest in bad weather they can be mortally wounded as they can be blown against the rocks. The young birds are attacked by adults if unattended. Once they leave the nest they stay at sea learning to fish and fly, their flight skills being too poor for them to return to the breeding ledges. Northern gannets have only one brood a year. The survival rate for young birds for their first four years is 30% and the annual survival rate for adults is 91.9%. The typical lifespan after becoming adult is 17 years, and the maximum known age is 37 years 4 months 16 days. Gannet pairs are monogamous and may remain together over several seasons, if not for all of their lives. The pairs separate when their chicks leave the nest but they bond again the following year. Should one of the pair die, the other bird will find another mate. Displays Northern gannets exhibit many types of aggressive behaviour while they are nesting. Confrontations normally only take place between birds of the same sex. Females will lower their heads before an aggressive male that is defending its nest: this will expose the back of the female's neck and the male will take it in its beak and expel the female from the nest. A female will not react if a male approaches a nest but it will react fiercely if another female approaches. The fights between males occupying nests for the first time are particularly intense. Such fights can last for up to two hours and lead to serious injuries. Birds lunge at each other and lock bills, wrestling for extended periods while neighbours peck at them. The fights are preceded by threatening gestures, which are also seen outside the breeding season. Males demonstrate ownership of a nest by gesturing towards their neighbours in a bowing display; their heads and beaks point down, and their wings are held up and away from the body, yet folded backwards. The male moves his head from side to side before bowing forwards. Males try to attract an