The Atlantic puffin's famous bill is built from horny plates over the underlying bill structure. Those plates grow before breeding and are shed after it, so a bird at sea in winter has a narrower, duller bill and a darker, greyer face than the one shown in summer photographs. The ornamental rosette at the gape is also lost.
The bill has a second, more practical distinction. Backward-pointing spines on the palate and a hinged jaw let a puffin hold a row of small fish crosswise while continuing to catch more, so adults arrive at the burrow with several sandeels or sprats at once rather than one. Loads of a dozen or more fish are ordinary, and much larger tallies have been reported.
What is misreported is the idea that bill colour signals age precisely. The number of grooves on the bill increases with age in a rough way, but it is not a reliable annual counter. The real conservation question is whether the small forage fish these loads depend on remain available near colonies.