adel ale ISKCs ed ORIDIS) 
same variation in colour characterizes the eggs of 
Molothrus bonariensis, which range from pure white 
through a spotty condition to eggs of a fine red through- 
out. Another fact which seems to show the compara- 
tive recentness of the parasitic habit is that Molothrus 
occasionally builds nests for itself, and inspects and 
shows a general interest in the nests of other birds, 
sometimes even altéring their structure and adding a 
finish. 
Bower Birps 
The last compartment of the Western Aviary has for a 
long series of years always contained examples of the 
bower bird (Pitlonorhynchus violaceus), and, as a rule, at 
least some attempt is made every year by these birds 
to construct the “ bowers’ which are known, by name 
at least, to most persons. This and the other kinds of 
bower birds are Passerine birds with no special features 
of structural interest except the difference, so marked, 
in the coloration of the two sexes. In the present 
species the male is a glossy violet shot black, while the 
female is a speckly greenish. Itis the minds, however, 
rather than the bodies of these birds which are of such 
great interest, and so hard to understand. It is in- 
variably the case that when there is a considerable 
difference of appearance between the two sexes, when 
sexual dimorphism, as it is called, occurs, that the male 
bird is the more brilliant in its hues of the two, and that 
its brilliancy of hue is emphasized by various antics 
which are performed in the breeding season; this 
behaviour is, it is thought, for the delectation of the 
hen, and as an attempt to gain her favours at the ex- 
expense of a less ably performing and duller-hued rival. 
As a matter of fact, such performances are not exclu- 
sively indulged in at the breeding season by all these 
diversely coloured birds. With the bower bird this 
159 
