Feature Articles

Diet-induced Plumage Erythrism as a Result of the Spread of Alien Shrubs in North America

Jocelyn Hudon and Robert Mulvihill

Many species normally bright yellow have been turning up with abnormal orange-to-red feathers in eastern North America and the American Midwest.  In addition to the well-documented orange tail-banded Cedar Waxwings, aberrantly reddened feathers have been recorded on Yellow-breasted Chat, Kentucky Warbler, White-throated Sparrow, Baltimore Oriole and Northern Flicker.  The birds are suspected of having acquired a carotenoid of deep red color (rhodoxanthin) from their diet, likely from the berries of two species of exotic bush honeysuckles (Morrow’s and Tatarian honeysuckle and their hybrids) now well established throughout eastern and Midwestern North America.  Using a set of well-defined criteria, we have compiles a preliminary list of species, plumages, feathers and feather tracts likely affected by the unusual carotenoid, and the U.S. states and Canadian provinces where they occur.  To accomplish this, we consulted banders at banding stations and browsed images of birds posted on the World Wide Web.  We report instances of obvious reddening of the plumage (i.e., erythrism) or the presence of rhodoxanthin in 15 species of birds, including several that ingest fruits only sporadically or seasonally, over a span of at least five decades.  Our summary includes many examples of aberrantly colored birds in eastern North America, including southern Canada, and the Midwest, but also farther west (Alberta, Montana and Idaho) and in southern areas where these birds overwinter.

 

Age determination of Swainson’s Thrush using the Distal Marginal Coverts

Blaine H. Carnes

The Swainson’s Thrush (Catharus ustulatus) undergoes a partial preformative molt resulting in molt limits within the median and greater coverts and alula.  As in other Catharus, distinct buff, shaft streaks to the juvenile median and greater coverts may be lacking and can wear off in many birds, sometimes making precise age determination difficult.  However, most juveniles have buff streaking to the distal marginal coverts located under the alula, which often can be retained in the preformative molt, making this another useful feather tract to examine when aging this species.