Cedar waxwings (Bombycilla cedrorum) are named for the bright red, waxy “droplets” that form at the ends of their secondary flight feathers. These “droplets” are appendages or extensions at the end of the rachis (central shaft of the feather). Both males and females may have these appendages that resemble red wax.
The waxy appendages are colored by astaxanthin, a carotenoid pigment, that gives red fruit its color. Second year birds have no or few appendages, often just nubbins at the end of the rachis. As cedar waxwings age the number and size of appendages increases.
The function of these red feather tips is not know for certain. Mountjoy and Robertson, writing in The Auk (1988), showed that cedar waxwings mated assortatively according to the number of red feather tips, older birds with longer and more red “droplets” mated with other birds with similar red tips and younger birds mated with birds having no or few, small tips. Pairs of older birds nest earlier, have larger clutch/brood sizes and fledge more young. The authors hypothesize that the red appendages may function as symbols of age and status and serve in mate choice and social organization.
In March I photographed the cedar waxwing when an irruption of these lovely birds invaded the campground at Lava Beds National Monument (Siskiyou County CA). Look closely and the droplets are visible on the wing. When we unfortunately found a dead cedar waxwing I was able to examine the red appendages more closely.