22 U.S. NATIONAL MUSEUM BULLETIN 223 



bation. Nestling care is of value in that it provides opportunities for 

 observing atavistic behavior of parasitic species, and such behavior is 

 an indication of an ancestral mode of life. 



Adaptive Features 



Because attempts were made by R. Neunzig (1929a) and others 

 to see highly adaptive, mimetic evolution in the remarkable simi- 

 larities in the color of eggs, in the pattern of nestling mouth markings, 

 and in the nestling plumage of viduines and of their usual foster nest 

 mates, I must discuss these matters in some detail. It should be 

 stated at the outset that these similarities are more probably due 

 to community of descent rather than to any convergence developed 

 after the advent of brood parasitism. I find that I was anticipated 

 by Hoesch (1939) and by Chapin (1954, p. 547) in most of my argu- 

 ments given below. With regard to the mouth markings, Chapin 

 stated that "the Estrildinae and Viduinae are closely allied and that 

 the latter have retained such markings and papillae ever since the 

 two groups diverged. Natural selection, of coiu-se, may aid in keeping 

 them so closely alike." 



Possibly Neunzig was unduly influenced by the older classification 

 of Reichenow and others, who placed the viduines with Euplectes, 

 Coliuspasser, and their allies. This arrangement would cause hun 

 to wonder at the convergence of egg coloration, buccal decorations, 

 and Juvenal plumage of the parasites, and those of their estrildine 

 hosts. 



Egg coloration: As far as is kno^\^l, all viduines lay unmarked 

 white eggs, very similar to those of their usual estrildine hosts. As 

 might be expected, there are some hosts that lay spotted or mottled 

 eggs, which bear little resemblance to those of the parasite, but such 

 instances are in the minority. Neunzig assumed that the white color 

 of the eggs of the parasites was an adaptation possibly originated by 

 mutation and acted upon by selection through the response of the 

 hosts (he apparently implied only estrildine hosts). Actually, we 

 ought to attribute this similarity to the close relationship of the 

 two gi-oups. It seems highly dubious for such resemblance to have 

 come about in birds using domed nests because in the dark interiors, 

 of the nests, dilTerences in the eggs would be scarcely discernible to 

 the hosts. 



Mouth markings and reflection globules of nestlings: 

 These structures are of two kinds — spots of dark color on the inside 

 of the mouth and on the tongue that form a symmetrical, geometric 

 pattern sharply delineated from the very differently colored mouth 

 lining; and globular, apparently luminescent, but actually merely 

 highly reflective tubercles at the corners of the gape immediately 



