Plumage, Age and Mortality in the Arctic Tern

Ringed Arctic Terns were used to study the relation between age and plumage, especially the age of birds in the so-called pikei plumage.It is shown that some, but probably not all, two-year-old birds assume this plumage but that it may also be worn later in life, sometimes for one season only.It is not an old age plumage as was at one time supposed.2. The majority of Arctic Terns appear to breed first when three years old or more, though there is one breeding record of a two-year-old.Breeding in an extremely eclipse-like plumage but with relatively bright beak and legs is recorded.3. In the colony studied some of the younger males failed to get mates, apparently because of a shortage of females.Some of these birds formed triangular marriages with mated pairs and occasionally even helped in raising their family.4. The survival of 102 colour-ringed adults showed an annual mortality of Ió 0 p.