ESTHETIC BIRDS 



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 altering their structure and adding a 

 finish. 



BOWER BIRDS 



The last compartment of the Western Aviary has for a 

 long series of years always contained examples of the 

 bower bird (Ptilonorhynchus 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. It is 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 



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