A Hybrid Jay from Chiapas, Mexico
| Autor: | Miguel Alvarez Del Toro, Robert K. Selander, Frank A. Pitelka |
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| Rok vydání: | 1956 |
| Předmět: | |
| Zdroj: | The Condor. 58:98-106 |
| ISSN: | 1938-5129 0010-5422 |
| DOI: | 10.2307/1364976 |
| Popis: | In January, 1951, a lone and peculiar jay was observed and collected by Alvarez del Toro at Santa Rita in western Chiapas (fig. 1). It appeared more robust than the locally common Magpie-jay (Calocitta formosa) and behaved differently from it. The locality, northwest of Tuxtla Gutierrez, is five miles north of San Fernando, a small village recently renamed Villa Allende. The specimen was sent to the Museum of Vertebrate Zoology, and the interest aroused by it resulted in several visits to the area by Alvarez del Toro and Selander, in 1953 and 1954. Their efforts were directed toward obtaining information on geographic and ecologic distribution of the jays locally present and, if possible, further specimens which would help unravel the mystery presented by the one which Alvarez del Toro collected. Because the Santa Rita specimen superficially resembles Calocitta more than any other jay (see fig. 2), it was first thought that it could be a variant of the dark type of C. formosa which occurs in increasing proportion in populations west of Chiapas. Between the black-throated, dark-faced race (C. f. colliei) occupying the northwestern end of the species' distribution and the westernmost of the white-throated, light-faced races (C. f. formosa), there occur individuals combining color characters of these forms in various ways. This is in an area over which the distribution of Magpie-jays is virtually continuous. Even the main features of this intergradation are not known yet, but the mixed characters of specimens from this area, and particularly the incidence of contrasting individuals in single populations, indicate that the changes from the "formosa" type to the "colliei" type are manifest in fairly complex manner over an area that is large. Hence the view that the Santa Rita specimen might represent some extreme expression of this situation. Two other possible explanations for the peculiarities of this specimen were at first also entertained. It could be a hybrid between Calocitta formosa and Psilorkinus mexicanus. This possibility arises from the fact that the area in which the specimen was taken is one of the few where the distributions of these two large lowland jays meet and overlap (fig. 3). The last explanation was simply that we were dealing with a new species of jay, and in the light of the train of relatively recent surprises offered by the Mexican avifauna, this hypothesis did not seem to be too far-fetched. There are nine species of jays in the region of the Isthmus of Tehuantepec, and one more conceivably could occur. Witness the presence of Cyanocorax dickeyi in western Mexico and of other species with similarly restricted distributions elsewhere in Mexico and Central America. Field explorations by Selander, however, disclosed no habitat conditions which would strengthen the notion that a new species was involved. From October 10 to 21, 1953, and again from April 25 to 30, 1954, the area was examined by him to see if there were any habitat with distinctive features of vegetational structure and of substantial area, or if there were any patterns of habitat interspersion peculiar to the area, which could be the domain of the strange jay. No such situation was found, and although additional specimens of both Calocitta and Psilorhinus were collected, all these were normal. As no definite evidence of still a third kind of large jay in the area was obtained, the possibility that the Santa Rita specimen represented a new species was dismissed. Closer study of the specimen has led us to dismiss also the view that it is merely a variant of Calocitta. Rather, the totality of facts appears to favor the view that it is a hybrid, and the information now to be given is organized on this assumption. |
| Databáze: | OpenAIRE |
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