BIRDS 



349 



Certhidea is peculiar to the Galapagos Archipelago and is known 

 from every island of the group. We have only a small number of 

 specimens, seventy six in all, but the genus has been well discussed 

 by Rothschild and Hartert and we make only a few changes in the 

 disposition of the species as given by these authors. There are eight 

 varieties distinguishable, comprised under two species — C. olivacea 

 and C. cinerascens, characterized as their names imply, one by an 

 olivaceous color and the other by an ashy tone. 



Nothing is certainly known of the nidification and eggs of Cer- 

 thidea. We shot a female of C. olivacea olivacea at Iguana Cove, 

 Albemarle, from a nest containing three eggs. The nest was exactly 

 like that of Geospiza fuliginosa and the eggs were identical in size 

 and coloration with those of the same species (see p. 310). Hence, 

 since we have no other examples we hesitate in ascribing this nest to 

 Certhidea. 



The CerthidecB are insectivorous, differing thus from most of the 

 Geosfizce which live on seeds, but the lowest member of the latter 

 genus, G. heliobates, feeds entirely on insects. 



The song in some cases resembles the ordinary songs of Geospiza, 

 and there is nothing distinctive in their habits. The birds are to be 

 found from the shore to the tops of the highest mountains. 



The color of the young is very similar to that of the adult, the only 

 particular specialization of the adults is the rufous or chestnut throat in 

 the males of C, olivacea. The following is a description of a typical 

 immature bird. The characters apply to any variety of C. olivacea. 



Immature Male and Female ( C. olivacea^. — Above almost uni- 

 form dull olivaceous, the feathers of the head with dusky centers. 

 Wing and tail feathers dusky brown, both remiges and rectrices edged 

 with the color of the back, tipped with gray. The middle and greater 

 wing coverts broadly edged in most cases with bright rufous. Below 

 pale buffy whitish with a slight olive tinge, brownish-buff along the 

 sides. Bill brownish above, pale below. 



By a comparison of this description with the descriptions of the 

 young in the first plumage of the subgenera Cactosfiza and Cama- 

 rhynchus of the genus Geospiza, it will be seen that the two almost 

 duplicate each other (see pp. 277; 284). Furthermore, the rufous 

 wing bands are characteristic of the first plumage of all the Geospizce. 

 This general resemblance in color between the young of these two 

 genera is, in fact, so striking that it is very suggestive of an actual 

 relationship existing between them. If such should be the case, 

 Cert\idea would be lower than any of the Geospiza, since the adults 



