When I lived in NYC, I occasionally went to Jones Beach for the day. I felt sorry for the old grey-mottled sea gulls who, unlike their younger, pristinely white compatriots, were spackled and speckled with grey marks. Their bedraggled state struck me, the hippy chick from Oregon, as yet another sad manifestation of the city's grime and decay.
WRONG. The speckled and strippled sea gulls are in fact the juveniles while the unblemished, snowy-white birds are the adults; it takes a few years for gulls (like eagles) to achieve sexual maturity, which is indicated by the snow-perfect appearance.