58 RUDOLF SÖDERBERG, STUDIES OF THE BIRDS IN NORTH WEST AUSTRALIA. 
shortly after the moulting, which as in other raptorials seems to take place during 
the summer. : The same is the case with the specimen of the 17th of Dec., the 19th 
and 22nd of Jan. in the first group. 
Among the light transitional forms (group 3), the fixing of the-age becomes 
very difficult, and here I have not been able to class with certainty more than two 
birds as juvenal specimens (group b). That even among the nestlings there is to 
be found, as it were, a characteristic of the transitional form is very probable. 
Further it is to be emphasized that thighs are also subjected to variation. In groups 
1 and 2 they are always dark, in groups 3 and 4 darker or lighter, though not 
always corresponding to the more or less light under side. 
It is therefore specially interesting to note, that the dark spots along the sides 
of the throat are not subjected to any variation in these specimens. They remain 
the same both in the lightest as well as in the darkest type, only more conspicuous, 
of course, in the former. Such a constant characteristic in a species that varies Very 
much is certainly of an older genetic value. 
Ecological. — The brown hawk was one of the most common raptorials in 
these regions. It was seen both up on the mountains at Mowla Downs, out on 
the steppe around Meda and at the coast of Broome, etc. Specimens shot on the 
steppe had a very much worn tail owing to the fact that they kept to the ground. 
I have never seen the bird catch prey on the wing. To some extent it is a carrion- 
eater, at least in the winter, when it comes to human settlements. Otherwise I 
met with birds that were catching fish and had also eaten fishes. 
At the end of the summer, when they leave their breeding-places, the birds 
flock together in great numbers round inhabited places. Thus very many birds 
stayed during the winter in the neighbourhood of Broome and at the missionary 
station in Beagle bay. They told me that the bird was not so generally seen there 
in summer. It is not seen in flocks like the kite (M. affinis) but appears scattered 
every-where. Where it is found in such great numbers the latter species is absent. 
But in Derby, where the kite lived in flocks, the brown hawks were few in number, 
even rare. 
Among the collection of brown hawks from Broome and Beagle bay the light 
specimens are much more preponderant. In winter the juvenals are, of course, most 
common. 
The fearlessness of these specimens seemed to indicate, that the supply of food 
was very scanty. The bird lives on lizards. They never hunted other birds, and 
the small birds did not pay any attention to them. TI have noted a characteristic 
act of one brown hawk in order to exemplify its fearlessness and harmlessness as a 
hunter. I had shot a cuckoo, which had tumbled down from the top of a tall tree. 
A brown hawk, living in the neighbourhood, came there and flew round the dead 
bird. Again and again it tried to take it from the ground, although I stood at a 
distance of only a few gunlengths from the bird. TI fired. It was not frightened; 
on the contrary it came and perched in the tree so near to me that I might have 
touched it with the barrel of my gun. Hunger made it follow me a» bit of the 
