SUDAN BIRDS

A NOTE ON THE SYSTEMATIC KEYS AND
ABBREVIATIONS USED IN THE TEXT.
For the purpose of identification synoptic keys, giving characters
by which each species may be recognised, have been drawn up. These,
in many cases, have been taken either wholly or in part from other works,
and where this has been done acknowledgment is made in a footnote.
While using these keys it must be remembered that not only are they
wholly artificial and in many cases unscientific, but also that they apply
only to the birds of the Sudan, and would be merely misleading elsewhere.
Even within this country identifications made by their means should be
viewed with a certain amount of reserve, since there is always the possibility,
in a country of such vast dimensions, of species not previously
recorded, or even of species new to science, appearing. In spite of these
drawbacks it is hoped that the keys may be of some defimte help to those
desirous of adding to their knowledge of the bird-life around them. A
few minutes study of the diagram (Plate I), showing the names of the
various parts of a bird, should suffice to make clear any technical names
which have been found unavoidable. The measurements given are taken
as follows :—
TOTAL LENGTH—from tip of bill to tip of tail. (This is seldom made
use of, since it can only be taken from a bird " in the flesh.")
WING—from the " shoulder " or " bend of the wing " to the tip.
Measured, in the ease of small birds, with a ruler placed along
the under side and pressed close against the wing ; in big birds,
by means of a tape stretched along the outside.
DIFFERENCE BETWEEN PRIMARIES AND SECONDARIES—The difference
between the whole wing, as measured above, and the measurement
from the " shoulder " to tip of secondaries.
BILL—Measured from base of feathering to tip, in a straight line
along the culrnen, or, in the case of birds with a cere, from the
point of junction of cere and bill to the tip.
TABSUS and Tons—as indicated in Plate I.