KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 52. N:o |7. 19 
other possible method of throwing light upon this difficult problem except by giving 
as many different examples as possible, in order to deduce from them the prevailing 
tendencies in the moulting of the birds. 
As to the juvenals I have endeavoured to bring together whatever has been 
possible, but have only been successful in obtaining a series of plumages of different 
ages of some species, and then to give a detailed description of these and the cir- 
cumstances under which they and the species in general moult. 
Here it may be remembered that the eminent Australian ornithologists have 
devoted their attention to this question, though the information about it is very slight 
and sporadic and, this being the case, it does not embrace a homogeneous material. 
I am of opinion, however, that a really extensive investigation of the conditions 
of moulting will also give very valuable information about the sexual characters of 
the birds, and that this is the way by which knowledge will be attained about the 
age and development of these characters and, to some extent also, their origin. 
Another subject to which I have given attention is the discolouration phenomena, 
that are clearly seen in a great many of the birds plumages at the end of the dry 
season or earlier. The cause is to be found in the insolation, where not even dust 
additions, viz. sand, has come to. For the description of the plumage characteristic 
of the birds, living in such hot and permanently sunlit zones of the earth as these, 
it is a matter of importance that this cireumstance should be laid stress on, when it 
appears as clearly as is the case here. (Platel, fig. 1, 2 and 3 are striking examples hereof.) 
In another species, Merops ornatus, the discolouration has created a blue tint in the 
plumage instead of the original greenish one, and in the case of Anthus australis 
tribulationis, it has caused such a change that I should not hesitate to place the 
species in the subspecies subrufus unless the habitat is known. Other details about 
this are contained in the special part. 
In the following survey there are duly given my conclusions in general about 
the habits of moulting of the birds, its periods and some instances of the mor- 
pbological changes of the feathers in connection with them. For information about 
the plumage of the young birds to the extent I have been able to give it, and their 
moulting, I may refer to the later part of this treatment. 
The importance of the rainy season for the animal and plant kingdom in a 
land with the West Australian climate has been described before. There I have 
specially indicated that feature which appears very clearly in the life of the birds 
during the remaining and greater part of the year, namely the »nomadic life». An- 
other feature, which is also connected with the climatic conditions is moulting of 
the birds. In that respect it is the rainy season, which exerts its influence, and — 
one is inclined to say — lets what is old and withered to develop into the fresh 
and new just as the faded plants are replaced by green grass and flowers. 
But from that it may be observed that both the time of moulting and that 
of breeding are less restricted to certain periods of short duration to a much smaller 
extent than in the case of the birds in the northern hemisphere. In North West 
