26 RUDOLF SÖDERBERG, STUDIES OF THE BIRDS IN NORTH WEST AUSTRALIA. 
building. A decrease in the number of points of attachment used, and a firmer 
technical ability has been developed (see below). 
The direct observations, which I was able to make concerning the nest-building 
of the birds in West Australia, were confined to observations of Artamus and Ptilotis 
forms and also (as far as I can say; the species could not be defined wich certainty) 
of Stigmatops. 
Fig. 10. Nest of Stigmatops from Dampier land. 
In Derby I thus observed, in the middle of January 1911, when the first- 
mentioned bird was building its nest, which belonged to the type that requires a 
firm substructure for its base. The nest was at first constructed as a transparent 
framework on a platform-shaped heap of twings. This intermediate bed was added 
to both from without and within by the female bird with coarser materials of twigs, 
fine roots and grass. 
In the case of Ptilotis the state of things was quite different. As a means for 
fastening the bird took the points between which the nest was to be suspended. 
