[quote=Rasmus Boegh;1567482]Above is about the vetenarian (and herpetological?) definition, i.e. of no direct relevance for their use in birding, where the above description is partially correct – partially incorrect (cf. definitions in specific ornithological references in earlier posts of this thread). Secondly, this thread is 4+ years old. Many things have happened since then. For birding the most significant is perhaps the article by J. N. Davis in Birding
39(5) dealing with color abnormalities in birds and terms used to describe them.
I must disagree. One of the problems with literature out there is there are too many people who do not use the correct definitions and that leads to confusion. The scientific and medical fields do have a standard set of definitions for a reason. When laymen begin to throw words around in the improper context, generating erroneous definitions, it leads to a large amount of confusion.
Moreover, when scientists that do not have a firm grasp on the pathogenesis of any conditions start using definitions to include a number of different pathologic conditions it leads to confusion in the academic world as well. Imagine the confusion if people started calling piebaldism vitilligo. Or leucism albinism (they do come from the same root and do mean the same thing - white). The result is confusion and a breakdown in communication. At present in the literature, including mammology, ornithology and herpetology, the technical definitions of leucism are not used correctly and not associated with the actual cause of any pigmentary condition. The result is that anything with white on it is being called leucism as long as it is not totally white with red eyes. There are forms of albinism where the defect is in a different part of the melanin cascade that produces blue eyed albinos in many species, but I have actually seen texts call this form of albinism leucism. That is inexcusable for anyone with a scientific background to do.
A good example is several texts and (of course websites) refer to "partial albinos." Where the pigment is reduced but not absent. This condition is known as hypomelanism and is a genetic defect where the melanophores produce reduced amounts of pigment. It is not leucism and not synonymous with leucism.
Secondly, if you have not been keeping up with phylogenetics Aves is not considered a class anymore but is placed under Reptilia under Archosauria. Therefore the herpetologic definitions have been applied. In fact they have been more or less accepted by paleontology for years and the rest of the biological sciences are just now catching up.
Lastly, I e-mailed the owner of http://veterinaryherpetologist.blogspot.com/
and asked him about bird pigments and leucism. He posted a reply on his blog earlier today that some might find interesting.
Sorry, I hope this does not sound terse, but I have been a biologist for a number of years and have noticed a real terminology problem in the sciences, especially in areas like these. The more general sciences like mammology, herpetology and ornithology have largely remained ignorant and failed to keep up with the more hard nosed, clinical sciences like medicine, biomedicine, molecular biology, biophysics, biochemistry, physiology, cellular mechanics and cellular biology. I could go on with that list, but I will not. I just think that if you consider the fact that of all the peer reviewed literature that is published in scientific fields each year, a conservative estimate is that, about 60% is junk and gets by not having being reviewed by those with real expertise in the field. Also, books that have not been peer reviewed are often riddled with falsehoods, and most articles that appear in hobby magazines are loaded with opinions that have no scientific data to back them up. So I get a bit edgy when I see a definition used that is archaic or downright incorrect, because it makes communication that much harder. So forgive my terseness, but it is so exasperating to have a defined term used with 14 different definitions that are not correct.