[Illustration]
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.