Thanks Peter, I have since learnt from others on Facebook better. Michael Retter replied on Facebook, where I shared it to ABA's page. He said that he like to call birds like this Hermit Thrush, "hypomelanistic" and then followed up with another comment.
--- quote --- There is a great article in Birding (39.5: 38) about pigment abnormalities in birds. It's from that article that I first learned of the terms "hypomelanistic", "amelanastic", and "hypermelanistic". Two key passages: "Melanins are the most prevalent pigments in birds. They produce almost all of the black, brown, gray, rufous, and buff shades and patterns, and they come in two general types--eumelanins and phaeomelanins... Eumelanins are more common and predominate in black and brown feathers, whereas phaeomelanins are less common and predominate in chestnut and rufous feathers...The relative proportion of these two pigment types, therefore, determines most colors...the ruddy throat of a Barn Swallow owes its color mainly to phaeomelanins." "The history of the term leucism is ... convoluted and controversial. It was first applied exclusively to the particular condition that results in all-white plumage or pelage and normally pigmented eyes and skin (Rensch 1925). Several decades later it was used for the abnormal condition that results in the dilution of plumage pigments (Harrison 1964). And more recently it has been applied to everything from an entirely white plumage to a single white feather (Buckley 1982). Harrison's usage appears to be the most widely recognized today [2007], but many still favor Buckley's definition. No matter which definition you prefer, however, the term leucism falls short in its usefulness for classifying color abnormalities in birds because it does not account for loss of pigment in unfeathered areas [such as in this Hermit Thrush's bill]." ---unquote--- Very interesting and certainly the best bird I have seen for a while. One of those birds that sticks with you and becomes real learning moments. Anders Peltomaa On Sun, Apr 24, 2016 at 5:52 PM, <[email protected]> wrote: > A very interesting and unusual looking bird. However, I would not call > this leucistic as there are no areas that show a complete lack of pigment. > This is clearly what is technically known as a dilution. It is caused by > one or a number of genes that deposit melanin in a lower than normal > concentration. > > Peter Post > > > Sent from my iPhone > > On Apr 24, 2016, at 3:22 PM, Anders Peltomaa <[email protected]> > wrote: > > Hi all, > > Yesterday, I and many other birders saw this exceptional Hermit thrush in > Central Park. None in my group had ever seen anything like it, and some in > the group have 50+ years of birding experience so calling it exceptional is > not an exaggeration. > > Photo by visiting French birder Hubert Pottiau. > <https://www.facebook.com/profile.php?id=100010342935903> > > https://flic.kr/p/GsFaeD > > good birding, > > Anders Peltomaa > Mannahatta > -- > *NYSbirds-L List Info:* > Welcome and Basics <http://www.northeastbirding.com/NYSbirdsWELCOME> > Rules and Information <http://www.northeastbirding.com/NYSbirdsRULES> > Subscribe, Configuration and Leave > <http://www.northeastbirding.com/NYSbirdsSubscribeConfigurationLeave.htm> > *Archives:* > The Mail Archive > <http://www.mail-archive.com/[email protected]/maillist.html> > Surfbirds <http://www.surfbirds.com/birdingmail/Group/NYSBirds-L> > BirdingOnThe.Net <http://birdingonthe.net/mailinglists/NYSB.html> > *Please submit your observations to **eBird* > <http://ebird.org/content/ebird/>*!* > -- > > -- NYSbirds-L List Info: http://www.NortheastBirding.com/NYSbirdsWELCOME http://www.NortheastBirding.com/NYSbirdsRULES http://www.NortheastBirding.com/NYSbirdsSubscribeConfigurationLeave.htm ARCHIVES: 1) http://www.mail-archive.com/[email protected]/maillist.html 2) http://www.surfbirds.com/birdingmail/Group/NYSBirds-L 3) http://birdingonthe.net/mailinglists/NYSB.html Please submit your observations to eBird: http://ebird.org/content/ebird/ --
