On the Moulting of the Diurnal Birds of Prey. 243 
XVI. On the Moulting of the Diurnal Birds of Prey. 
- By J. G. Goopcutp, F.Z.S., M.B.O.U. 
(Read 20th April 1892.) 
[ ABSTRACT. ] 
The writer aimed at showing that, in captivity, three types 
of change of plumage may be observed in the birds of prey, 
and he argued that to a certain extent this may prove to be 
true also in regard to their moult in a state of nature. In 
the first of these the bird moults several years in succession 
into much the same style of plumage as that of its first 
year’s dress. This is the case with some species of Aquila 
and of Haliaetus in captivity, and it was particularly notice- 
able in a female Condor living for several years at the 
London Zoological Gardens; each year’s moult gave rise to 
a new dress, differing little, if at all, from that of the first 
year. The writer made water-colour drawings of this bird 
for Mr Gurney and others, with a view to recording any 
change that might arise. At last a few lead-grey feathers 
began to appear amongst the older brown, and the bird’s iris 
showed evident indication of a change to the garnet colour 
characteristic of that part in the adult; but the change had only 
just commenced when the bird died. Mr Gurney regarded 
this as a case of deferred maturity; but was uncertain 
whether the bird, in a state of nature, would have moulted 
more than two or three years before assuming the adult dress. 
In the genus Spizaetus, a change of a different nature may 
be observed. In these the approach to the fully adult 
plumage is made by successive changes extending over 
at least four moults, each dress being more like the adult 
than that which preceded it. In strikingly.coloured species, 
like Sp. ornatus or Sp. coronatus, this successive change of 
plumage can hardly fail to attract attention. That in a 
state of nature the adult plumage of the Spizaeti is reached 
by successive steps is clearly proved by an examination 
of any large series of skins. Geranoaetus appears also to 
follow the same rule as Spizaetus in this respect. 
A third type of moult, and the most prevalent, is that 
