THE BIRDS OF AUSTRALIA. 
bird and there leaves it. The egg is hatched by the small bird and the young 
Cuckoo then ejects its neighbouring (and rightful) chicks and is reared by the 
foster-parents, who continue to feed it after it has left the nest. The dubious 
points are the number of eggs laid, the manner of nest selection, the relation 
of the egg coloration of the Cuckoo to that of the bird selected, the rejection 
or acceptance of the strange egg by the foster-mother, and such-like queries, 
capable of much discussion but of doubtful settlement. Other features of interest 
are the small size of the Cuckoo’s egg as compared with the bird itself and the 
incubation period being shorter than eggs of the same size. Some of the above 
items are not concerned with all the species, but are generally given as being 
of interest in the typical species of the Order. 
The gradation of the three groups Cuculus, Cacomantis and Chrysococcyx 
is very peculiar, as it is marked in most particulars, size, coloration, length of 
tail, etc. ; yet it is possible we see here again instances of convergence, as often 
met with when dealing with ancient groups. Thus Cuculus is close to Cacomantis^ 
and Heteroscenes is somewhat intermediate, so much so that it was first classed 
in one group and then in the other when the two groups were recognised. The 
Bronze Cuckoos have been continually separated from Cacomantis on account 
of their bronze coloration and smaller size ; but here again some species are 
dull, while it is obvious that the bronze species are separable into groups and 
have evolved more or less independently. Thus, the African series seem quite 
distinct from the Asiatic and Australian series; and, moreover, two or more 
sections can be seen among the former as well as among the latter, the sections 
being different in each case. I discussed these some years ago and concluded 
that the plumage changes would serve as a good basis for accurate differentiation, 
and since then I have not altered my opinion, though modification must be 
necessary in this as in most other matters with more material. Thus I conclude 
that geographical considerations must be maintained at a high value, whereas 
most workers minimise such. In the present instance the above named groups 
are of similar geographical range, and it is possible that Heteroscenes is the 
Australian representative of Cuculus, while Cacomantis is similarly allied but has 
degenerated more quickly and become separable into many forms, specific and 
subspecific. Then the Bronze Cuckoo of Africa have arrived at a similar 
coloration to those of Malay -Australasia, though derived from a different source. 
These small Cuckoos are common in species in Malay-Australasia and form a 
complex group, and as noted above the best guide to their affinities appears to 
be through their plumage changes, which somewhat differ as will be shown later. 
The diversity of the species negatives consideration of the extra-limital 
species such as occurred commonly in previous orders, but one or two items 
may be recorded. 
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