. The development of the beak of the Atlantic Puffin Fratercula arctica as shown by birds ringed as
chicks and subsequently seen in the breeding colony. Typically, a bird in its first year has a trace of a bill groove,
in its second year one sometimes ill-defined groove, in its third year one and a half grooves, and in its fourth
year two complete grooves. A few individuals never develop more than two grooves but most older birds have
two complete grooves and at least a trace of a third groove. © Mike P. Harris