302 THE ESSEX NATURALIST.
were barred to be enumerated. A male Bewick's Swan provided
the most striking demonstration of subordinate barring that
has come to my notice, many parts of the plumage being affected.
Twelve specimens of birds in an advanced state of albinism were
examined to ascertain if feathers devoid of their normal
pigmentation retained or exhibited subordinate barring. It was
found in all these specimens, much as it was found in the
specimens forming the main part of the enquiry. In the case of
a Song-Thrush some of the feathers of the tail were white and
some retained their normal colour, and it was found that
feathers of both colours were similarly barred. The twenty skins
of Blackbirds—examined to explore how far a species might be
affected—were found to be subordinated barred in conformity
with the results of the main part of the enquiry.
The results of the enquiry suggested that subordinate barring
is a character common to birds and it cannot be said to depend
on sex, age, colour, locality or season for its appearance. I came
to the conclusion that subordinate barring of feathers is probably
due to structural modification of feathers, in the same way as
colours are produced by structural adaptation of feathers.
After the publication of my paper three important contribu-
tions to the subject came to my notice. Bars in Flight Feathers
was published by H. and J. R. Michener, (cf. The Condor, vol. xl,
1938, pp. 149-160). These authors, as the result of an enquiry
of some extent, came to the following conclusions :
1. Each of the bars in a flight feather, similar in appearance
to a watermark in paper, represents a day's growth of the
feather.
2. Most flight feathers of post-juvenal or later plumages
show bars.
3. Juvenal flight feathers usually show no bars, though
occasionally the bars are visible, especially in the tail.
4. Bands lighter than the normal colour are not uncommon
across the wings or the tail or both of a juvenal bird. In
rare cases all the body feathers also show these bands,
which are probably due to some metabolic deficiency
resulting from some changed condition in the bird's life.
5. Bands may occur in post-juvenal or later plumages if a
group of flight feathers is replaced simultaneously, and
if the bird during the growth of these feathers experiences
conditions which will cause bands.
6. The presence of bands or the absence of bars justifies a
strong suspicion that the feather is a juvenal feather.
7. The presence of bars justifies a strong suspicion that the
feather is not a juvenal feather.