Adult breeding Chinstrap Penguins (Pygoscelis antartica) have larger b
ills than one year old individuals, whereas the flipper length does no
t differ. Therefore, bill size increases with age during the juvenile
stage. The allometric relationships of both bill length and bill depth
with flipper length do not differ between age groups. The relation of
bill length with bill depth does not differ between adults and juveni
les, suggesting no change in bill shape with age. If the random sample
s of adults and yearlings represent a similar proportion of males and
females, these results do not support sex divergence in bill growth af
ter the first year of life.