XIX 
THE COLOURS OF BIRDS 
255 
red feathers of the male king paradise bird ( Cicin - 
nurus regius ) owe their brilliancy. This pigment, 
called zoorubin by Krukenberg, occurs freely in 
various species of the birds of paradise, chiefly in 
the males, and has also been found in one of the 
Indian trogons (Pyrotrogon diardi) in the male, 
in the great bustard (Otis tarda), and in certain 
varieties of the common fowl. 
Zoorubin is soluble only in dilute caustic soda, 
from which it is precipitated by the addition of 
acid as a dull brownish mass. Its solutions show 
no bands, but give two well-marked reactions. If 
cold concentrated sulphuric acid be poured cautiously 
into a test tube containing the solution, a blue or 
green ring forms at the junction of the liquids. 
Again, if the solution be rendered feebly acid and a 
trace of copper sulphate added, a bright cherry-red 
colour is produced. The pigment does not appear 
to contain iron or copper. 
This list almost exhausts the known pigments of 
birds, and its two most striking features are, on the 
one hand, its uniformity, and on the other, the occur¬ 
rence of peculiar and rare pigments like turacin in 
exceptional cases. It may, of course, be suggested 
that the impression of general uniformity is due 
to ignorance, and that many families of birds may 
contain peculiar and as yet undescribed pigments. 
There is, of course, no proof that this is not so, but 
at the same time the observations which have been 
made by Krukenberg and others tend to prove at 
least the very wide distribution of lipochromes and 
melanins, while they have failed to disclose any pig¬ 
ments of the uric acid group. The presence of 
