24 RUDOLF SÖDERBERG, STUDIES OF THE BIRDS IN NORTH WEST AUSTRALIA. 
find -on the ground. Remarkable exceptions from this rule are, however, to be found 
among hawks and falcons. The West Australian half-desert, is, however, the domicile 
par excellence of lizards. 
The number of these animals is very large, although the number of species is 
not in proportion in that respect to the numbers of individuals. Several species are 
climbers. These too were so common that the trunks of the trees showed worn paths, 
produced by the frequent visits of the animals to the trees. The dimensions of these 
tree-climbers was, of course, varied, but many of them reached a total length of 
as much as 7—8 dem. In addition to these the reptile-fauna of West Australia in- 
cludes a by no means small number of serpents, some species of which spend the 
greater part of their life in the trees. The part the reptiles play for the bird life 
that inhabits these sparse savanna woods is undoubtedly very important. As we 
have already mentioned the circumstances in these parts of the earth are very 
favourable for giving them an importance that assumes an active interference in the 
existence of the birds. 'The most important way in which this may perhaps make itself 
felt is by lizards and serpents trying to find out the birds nests in order to feed on 
their eggs and young. 
It is well known that this explanation is given to account for the origin of 
certain characteristically different shapes of birds nests in other parts of the world. 
West Australia cannot show many instances of a high state of perfection in 
nest-building called forth as a protection against lizards and serpents. But among 
some species of Timeliide and Glyciphilide are to be found very carefully built toose 
hanging nests, fixed to the top of a branch, especially one which hangs over water. 
These nests remind one of similar circumstances among certain Indian weaver-birds” 
nests. 
The very uniform type of nest-building prevails among nearly all Meliphagide 
and among a great many other small birds. It is the cup-shaped nest, most fre- 
quently hanging like a bag on: the extreme points of the branches of the trees or 
bushes. I often saw nests so exposed that they could be discovered at a' distanec, 
partly because of their open situation, partly because of the light colour of the 
building-materials (vegetable wool). 
In this method of nest-building there was a tendency to place the nest as far: 
out in the periphery of the tree as possible, to fix it on the points of the branches 
which were farthest out and weakest. The nests built in small bushes also had this 
position. Evidently this position particularly in the last-mentioned case, would not 
have been so suitable if a danger from outside had threatened — that is to say »from 
outside», from the nearest surroundings — used in opposition to »from within», from 
the circumference of the tree or bush. 
If danger is to be expected from the last-mentioned direction the nest is pro- 
tected better the more it is moved away from the inner parts of the leafage. 
This phenomenon occurs, it seems to me, in West Australia because of the 
frequent presence of the tree-climbing reptiles. These are accordingly the principal 
cause of this choice of situation and to some extent, of the manner of building that 
