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Show 1867.] MR. O. SALVIN ON THE BIRDS OF VERAGUA. 131 The geographical position of the portion of Veragua we are now considering, situated as it is between Panama and Costa Rica, certainly suggests that its ornithological fauna would consist of species belonging to each fauna, with the addition of some few species peculiar to the district. Such appears to be actually the case. Rather more than one-half the birds are also found in Costa Rica, while rather less than two-thirds are found on the Panama Railway. About one in ten has not been hitherto seen beyond its limits. Rather less than three in seven extend beyond Panama into the southern continent of America, while three in seven extend northward into Guatemala, Mexico, or the northern continent of America. These proportions show that this district most resembles the Isthmus of Panama as regards its birds, that it has a less strong affinity to Costa Rica, and that out of the wide-ranging species a rather larger proportion belongs to more northern regions than to southern. It would be necessary to compare closely the birds of this district with those of Costa Rica to ascertain accurately where the balance of their relationship lies. The presence of several peculiar forms, such as Cephalopterus, Chasmorhynchus, Oreopyra, Microchera, &c, suggests that Veragua belongs zoologically to Costa Rica, and that Panama maintains a strictly derivative fauna, and has at no period of the geological history of the isthmus ever been a centre of segregation. On the other hand, it is to Costa Rica and Veragua united that we must look to find the origin of most of the species now found on the Isthmus of Panama, it being evident that this district has for a long period occupied a position as an island, or one of the islands which lay between the two continents at a time when the two oceans were united by two or more channels. It is for geologists to tell us where these divisions were situated. An obvious one, separating Costa Rica, Veragua, and Panama from the southern continent, is the line from the Atlantic bay of San Bias across to the mouth of the Bayano on the Pacific. Regarding Costa Rica, Veragua, and Panama as a whole, there are indications, in the Humming-birds at least, of some separation having existed between the extreme ends of the district, Microchera albo-coronata of the southern extremity being represented by M. parvi-rostris at the northern, Chalybura isauree by O. melanorrhoa, Thaumantias chionurus by T. cupreiceps. As no instance of representative forms occurs in other groups of birds, it is perhaps more probable that the local distribution of particular plants from which these birds take their food limits the range of each race than that any actual geographical barrier has given cause to this divergence. I hope shortly to return to this subject in a paper on some collections from Costa Rica; but I may state that m y present view is that this district, viz. that included from the rise of the mountains to the northward of the line of the Panama Railway to the southern shore of the lake of Nicaragua and the river San Juan, forms the key to the peculiarities of the Central-American bird-fauna. Previously to the separation indicated between Costa Rica and the southern continent, but when the more northern strait, where the lake of |
