CAMPHUYSEN CJ (1992) Actualities: Looking for bird long bones: a call. LIMOSA 65 (3): 136-136.

many forms of research is important to to know exactly how old a bird. Some seabirds plumage gives a rough indication, because the dress several of the immature birds (gulls, Gannet). In most birds, however, is that not. To change the plumage of Nordic Glacialis Fulmars Fulmaris after fledging are not, even if these birds very old (40-50 years?). Also research the possibilities of dead birds is limited. Inspection of the genitalia gives condusie only as never bred / ever brood and the presence of a bursa is Fabricii aileen useful for juveniles (young or subadult) of the residual separation

[free pdf] [dutch summary]