Jaw Musculature of the Mourning and White-winged Doves Part 2

My dissections demonstrated that, in relation to the size of the doves, the jaw musculature of all the specimens investigated was so nearly alike that only one major difference was detected. _M. pseudotemporalis profundus_ appeared to be enlarged in the White-winged Dove. This might have been predicted, since the white-wing was also shown to possess an elongated beak, presumably an adaptation for nectar-feeding, which would necessitate additional muscle development in order to compensate for the added length. Measurements recorded from several skulls indicated that the heads of the birds (excluding the beak) are nearly proportional.

Perhaps plumage patterns are the most widely used characters for determining generic relationships of birds. Ridgway (1916:339-385) followed the columbid cla.s.sification of Salvadori (1893) using plumage patterns and body proportions to distinguish between the genera. In the genus _Zenaidura_ he included the unique specimen _Zenaidura yucatanensis_, and he placed _auriculata_ in _Zenaida_. The White-winged Dove was referred to a separate genus, _Melopelia_. He described the genus _Zenaidura_ in the following manner:

"Plumage of head, neck and under parts soft and blended; bare orbital s.p.a.ce moderate, broadest beneath eyes.

Coloration plain, the proximal secondaries (sometimes adjacent wing-coverts and scapulars also) spotted with black; rectrices (except middle pair) with a black band across postmedian portion, the apical portion paler gray than basal portion, sometimes white; a small black subauricular spot; adult males with head, neck and anterior under parts more or less vinaceous and sides of neck glossed with metallic purple."

He noted that the plumage of _Zenaida_ was almost precisely as described for _Zenaidura_. Also, although all members of _Zenaida_ reputedly possessed twelve rectrices, a characteristic of the genus, it was later found that _auriculata_ possessed fourteen rectrices. The species was promptly placed in the genus _Zenaidura_ by Peters (1934:213-215). In plumage and coloration, _Melopia_ was described as similar to _Zenaida_ and _Zenaidura_ but without black spots on the wings.

The White-winged Dove also has twelve rectrices, but Bond (1940:53) and Goodwin (1958:330-334) considered the number and shape of rectrices to be of minor importance when compared to the h.o.m.ologous markings of the plumage. Goodwin stated that his conclusion was emphasized by the fact that the tail of _auriculata_ is intermediate in length and shape between those of _macroura_ and _aurita_. In summary Goodwin "lumped"

the genera _Zenaida_ and _Zenaidura_ under the genus _Zenaida_.

Nidification

It has been adequately doc.u.mented that members of these genera closely resemble one another in their nesting and egg-laying habits. Bent (1932:407, 417), Davie (1889:157), Goss (1891:242) and Nice (1922:466) have described the two, white eggs of the clutch of the Mourning Dove.

They have also noted that their nests are composed mainly of twigs and may be constructed in trees, shrubs or on the ground. The Eared Dove has nearly identical habits (Bond, 1961:104), and a similar situation exists with the Zenaida Dove (Audubon, 1834:356; Bent, 1932:418-419).

Like the other species, White-winged Doves lay two white or buffy eggs per clutch and build frail nests of sticks (Bent, 1932:431; Wetmore, 1920:141; Baird, Brewer and Ridgway, 1905:377).

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.

SUMMARY AND CONCLUSION

The avian genus _Zenaida_ is currently considered to be distinct from the genus _Zenaidura_ by most columbid taxonomists. The jaw muscles of six Mourning Doves (_Zenaidura_) and five White-winged Doves (_Zenaida_) were investigated as to differences and similarities that might clarify the relationships of the genera. The sizes and proportions of skulls were also considered in 37 Mourning and White-winged doves and two Eared Doves. Larger size of _M.

pseudotemporalis profundus_, the muscle that functions simultaneously as an adductor of the lower jaw and retractor of the upper jaw, in the White-winged Dove was the character found in the jaw musculature that could be used to support the contention that _Zenaidura_ and _Zenaida_ represent distinct genera. Larger size of this muscle in the white-wing seems to be related to its elongated beak. The long beak apparently is used for nectar-feeding in flowers of the Saguaro Cactus.

Excluding the beak, skulls of the white-wing and Mourning doves are of nearly the same shape. Previous investigators have shown that in _Zenaida_ and _Zenaidura_ plumage patterns are similar, nesting habits and eggs are nearly identical, blood proteins are similar, and one "intergeneric" hybridization in nature is known.

Consequently, it is concluded that species of the two alleged genera are congeneric, and I agree with Goodwin (1958) that the genus _Zenaida_ (Bonaparte, 1838:41) should include the Mourning Dove, Eared Dove, Socorro Dove, Zenaida Dove, and White-winged Dove. Their Latin binomina are _Zenaida macroura_, _Zenaida auriculata_, _Zenaida graysoni_, _Zenaida aurita_, and _Zenaida asiatica_, respectively.

[Ill.u.s.tration: FIG. 1. Medial view of left ramus of lower mandible of Mourning Dove. 2-1/2.

FIG. 2. Lateral view of right ramus of lower mandible of Mourning Dove. 2-1/2.]

[Ill.u.s.tration: FIG. 3. Dorsal view of lower mandible of Mourning Dove. 2-1/2.

FIG. 4. Ventral view of lower mandible of Mourning Dove.

2-1/2.]

[Ill.u.s.tration: FIG. 5. Dorsal view of right quadrate of Mourning Dove. 5.

FIG. 6. Dorsal view of right pterygoid of Mourning Dove. 5.

FIG. 7. Ventral view of right quadrate of Mourning Dove. 5.

FIG. 8. Ventral view of right pterygoid of Mourning Dove. 5.]

[Ill.u.s.tration: FIG. 9. Right lateral view of skull of Mourning Dove. 2-1/2.

FIG. 10. Ventral view of skull of Mourning Dove. 2-1/2.]

[Ill.u.s.tration: FIG. 11. Cross section of skull of Mourning Dove; anterior view. 2-1/2.

FIG. 12. Dorsal view of right quadrate of Mourning Dove showing movement which protracts the upper mandible (broken line). 5.]

[Ill.u.s.tration: FIG. 13. Right lateral view of the jaw musculature of the White-winged Dove; superficial layer, 5.

FIG. 14. Right lateral view of the jaw musculature of the Mourning Dove; superficial layer. 5.]

[Ill.u.s.tration: FIG. 15. Dorsal view of the jaw musculature of the White-winged Dove (right side); superficial layer. 5.

FIG. 16. Dorsal view of the jaw musculature of the Mourning Dove (right side); superficial layer. 5.]

[Ill.u.s.tration: FIG. 17. Dorsal view of the jaw musculature of the White-winged Dove (right side); middle layer. 5.

FIG. 18. Dorsal view of the jaw musculature of the Mourning Dove (right side); middle layer. 5.]

[Ill.u.s.tration: FIG. 19. Dorsal view of the jaw musculature of the White-winged Dove (right side); deep layer. 5.

FIG. 20. Dorsal view of the jaw musculature of the Morning Dove (right side); deep layer. 5.]

[Ill.u.s.tration: FIG. 21. Ventral view of the jaw musculature of the White-winged Dove (_M. depressor mandibulae_ not shown). 5.

FIG. 22. Ventral view of the jaw musculature of the Mourning Dove (_M. depressor mandibulae_ not shown). 5.]