The point to be made here is simply this: If the species in question are to be considered congeneric then it might reasonably be expected that they would display some similarity in nidification and egg-laying. If their habits varied considerably it would not necessarily mean that their relationship was more distant, but similarities can usually be considered indicative of affinities because they are the phenotypic expression of the partially unaltered genotype of the common ancestor.
Interbreeding
Intergeneric crosses of columbids in captivity are common, but in nature there is little evidence that even interspecific crosses occur. Only one apparent hybrid between members of the genus Zenaida and genus Zenaidura has ever been discovered. The individual was taken on the Yucatan peninsula of Mexico, and was described and named as a new species (Zenaidura yucatanensis).
Salvadori (1893:373), Ridgway (1916:353) and Peters (1934:213-215) agree that Zenaidura yucatanensis Lawrence is a hybrid between Zenaidura macroura marginella and Zenaida aurita yucatanensis. Ridgway (1916:355), however, notes that "... If Zenaidura yucatanensis Lawrence should prove to be really a distinct species, and not a hybrid ... unquestionably Zenaida and Zenaidura can not be separated generically, since the former is in every way exactly intermediate between the two groups." In the event that the unique type is a hybrid, the very fact of its existence supports the hypothesis that the genera are more closely related than is currently recognized.
Serology
There have been no investigations having as their sole purpose the clarification of the relationship of the genera Zenaida and Zenaidura. But some work has involved the comparison of the antigenic content of individual columbids with the antigenic content of a member of another species of the same family.
Irwin and Miller (1961) tested, along with other columbids, members of Zenaida and Zenaidura for presence of, 1) species-specific antigens of Columba guinea (in relation to Columba livia) which are designated A, B, C and E, and, 2) species-specific antigens of C. livia (in relation to C. guinea) which are designated A´, B´, C´ and E´.
In the first test all five species of Zenaida and Zenaidura possessed antigens A and C, and all but auriculata possessed E. None of the species gave evidence of the presence of the B antigen of C. guinea in their blood. In the latter test only macroura had A´, only asiatica had B´ (aurita was not tested for B´), and none had C´ or E´.
These results would indicate that the five species are similar regarding antigenic content of the blood, and the variation is not consistent within one or the other genus as presently known.