GREEN HUNTING JAYS TURN BLUE
Sometimes in "working out" a bird collection things get dull. In identifying the specimens, and writing down why they are this species, or that species, or subspecies, it seems routine; as though it were simply routine putting things in the categories ready for them.
Such was my feeling one day as I worked over Himalayan jays and magpies from Nepal. I'd done the yellow-billed blue magpie, and the red-billed blue magpie, which both fell into their places smoothly. Then I got out the literature, the pertinent keys, and descriptions for the next species, the green hunting jay. It's a beautiful, pale, apple-green bird, with a green crest, and set off by dark red wings. It checked with the descriptions, and I wrote Kitta chinensis, its scientific name, on the label. Then, to check the species' identification and to determine the subspecies, I turned to the collection, to the birds from India, Siam, and north Indochina, which should all be the same.
I pulled out the drawer—and blinked at the jays, rows of them; all pale blue with brown wings. I looked at the name on the case, on the tray, and the name on each specimen. They all said the same, Kitta chinensis chinensis, and it was the bird described as green, like my new specimen. It was uncanny. The new green specimens and the old blue ones were identical in size, in structure of bill, crest, feet, tail; they must be the same. And they were. The book, I found, described how the colors changed with age, and in John Gould's magnificently illustrated folio, Birds of Asia, published in 1861, he had the green hunting jay depicted both as a green bird with red wings and, in the background, a "blue" green hunting jay like our museum specimens. When alive, and when freshly killed, the birds are green. But with the passing of time the green changes to pale blue, and the red wings to brown wings. Probably my new specimen, now a year old, is less green than it was when fresh. And when twenty years old, like our museum skins, it will be blue too.
The riddle was solved, and it fits into a well-known phenomenon, "museum age" or post-mortem change. "Foxing," we call it for short. We see it in the male American merganser, where the lovely rich salmon color of the fresh bird becomes plain white. The emerald cuckoo of Africa has vivid rich yellow under parts when fresh, and this too becomes dingy white. Gray Canada jays become more brownish. Birds that are olive or other shades of green tend to become more olive; brown birds tend to become more russet or foxy (hence the term "foxing"). We keep all our specimens in dustproof, lightproof metal cases. The change is not caused by fading. Apparently it's a change in the pigment, perhaps from oxidation.
Taxonomists, the men who classify and name birds, have been fooled by it. Old skins used to represent the birds of an area may give a quite different idea of what they are like than do fresh skins, and when skins of different age are compared, the conclusions may be wrong.
Foxing is one of the pitfalls for the unwary taxonomist, and something he has to guard against.