Both males and females have red tips; both the number and size of the red tips increase with age; the red tips may play a role in mate choice and social organization (facts from the Birds of North America account).
And here's a trivia question. There are only 3 species of waxwings in the world. Can you name the other two? (Answer below.)
Answer: The other two waxwings are the Bohemian Waxwing (Bombycilla garrulus) and the Japanese Waxwing (Bombycilla japonica). Bohemian Waxwings have been recorded in Sonoma County, but they're only accidental visitors, with the last observation in 2005 according to the Birds of Sonoma County.