HETEROCHROSIS IN ESSEX BIRDS AND THEIR EGGS. 181
The work was carried out on the following lines. In the first
instance a description of each case was written, but on the
grounds of space some form of condensation was necessary. The
following definitions have been adopted :
Complete—Birds whose plumage is wholly white or approxi-
mates thereto. (It would have been preferable
to have used this for birds which are not only white,
but also have the eyes, bill and legs affected, but
the data at my disposal are too incomplete to allow
of this.)
Complete Partial—Birds whose plumage is uniformly affected,
but not to the extent of whiteness, for example
cinnamon-coloured birds.
Partial—Birds whose plumage is pied or affected in other
similarly irregular manner.
References are given for each species, so that all recorded
instances may be traced ; the unrecorded cases which are included
in their respective totals are extended beyond their particular
categories, followed in brackets by the month in which observed,
and other particulars so far as known. The data in many cases
are not complete, but all have been carefully considered and
placed under the category which seems most suitable.
ALBINISM.
Rook. Corvus f. frugilegus L.
Unrecorded.
Complete .. 5 1 (Young bird, June)
Complete partial 8 3 (1 young bird, light dove-coloured
with white bands round its feet,
1 brown, 1 slate coloured)
Partial .. .. 1
Total .. 14
Ref.: The Essex Lit. Journal; The Mag. of Nat. Hist. and Nat.
1860, pp. 51-3 ; The Birds of Essex (Christy) ; The Field,
vol. 63, p. 702 ; The Essex Nat., vol. 22, p. 320.