Friday May 17, 2013:  83 new of 25 species, 18  recaps.  New species:  Ruby-throated Hummingbird.   It was a chilly but otherwise lovely morning at the lakeshore today, with lots of birds heard (including a Cerulean Warbler) but fewer caught.  The Bander Training Class did much of the net-picking and banding, and everyone had the opportunity to watch our first three hummers of the season being banded by visiting bander Ember Jandebeur.  A Field Ornithology class from SUNY ESF came to visit mid-morning, and whenever there were no birds in the hand to see, they had their bins trained on the treetops.

Today, we captured another after-second year male American Redstart with an oddly colored tail.  The orange color on and under the wings was the typically bright “optic orange”, while the color on the tail was a washed out yellow.

A second American Redstart with an unusual tail

A second American Redstart with an unusual tail.

Curious about this color difference, I took a few minutes to research American Redstart pigmentation.  The orange color is caused by carotenoids ingested in the birds’ food, and it is differences in the amount of carotenoids that causes the different hues and saturations of color.  One study took a tail feather from 112 male American Redstarts in 12 locations throughout Central America and the Caribbean.  Since American Redstarts molt their tails shortly after the end of the breeding season, those tail feathers grew in at latitudes ranging from the Gulf coast of the US all the way to southern Canada.  The scientists then used stable-isotope analysis on those feathers to determine – within broad geographical regions – where those tail feathers grew.  Thus, they had a rough idea of where the bird was when it molted its tail.  They found that birds who molted at more southerly latitudes had paler tails, while birds who molted at more northerly latitudes had more vivid tails.  If that’s true, then we might suppose this bird molted in the southern US.  However, we’d also have to suppose that it molted its wing and body feathers significantly before its tail.  And then, how to explain yesterday’s tri-colored tail?  We might suppose that it bred and molted at a northern latitude, and then somewhere during its migratory route, lost half its tail and regrew it at a more southern latitude.  This is only speculation, of course, and I’m still open to competing hypotheses!   Andrea Patterson