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Show 1306 EEPORT OF THE CHIEF OF ENGINEERS. The Western Orange- crowned Warbler, ( Helminthophaga celata var. htiescens,) which is distinguished varietally, as it occurs on the west coast, mainly by its brighter coloration, is here decidedly paler, thongh still approximating more closely to this than to the interior and eastern form, H. celata. The same is true of Myiodioctes pwillus var. pileoJatus as compared with M. pusillus. The Song Sparrow of this region, though referable to the Pacific type, ( Melospiza melodia var. heermanni,) yet very distinctly approaches theAf. var. fallax of the middle province, and only a short distance to the east of the main chain will be found to merge into the latter. Perhaps, however, in no bird is this tendency toward variation better shown than in the remarkable thick-billed sparrow, ( Passerella iliaca var. megaryncha.) In its typical region, the southern coast range of California, the bill of this bird is enormously developed, till it becomes almost misshapen through its extreme depth. Coincident with this is a change of color, it being several shades darker than its representative from the interior, P. var. schistacea. Examples from the eastern slope, though unmistakably of this variety, show in* the modification of these peculiarities that many steps have been taken toward the schistacea form. The colors are lighter; the bill, though still much larger than is ever found in the latter bird, is perhaps scarcely half the size found in extreme examples of P. var. megaryncha. Other species showing a similar tendency might also be cited, all having the same significance, viz, a differentiation from the typical condition of their respective forms toward the interior type, coincident with their intermediate habitat. The small number of species of the Warbler family ( Sylricolida:) represented in the Sierra Range, as remarked by us during the season of 1875 in California, and again the past season on the eastern slope, as compared with the number found in the Rocky Mountains, is a matter of much interest. When the comparison is extended to the middle and Pacific provinces proper, nearly the same numerical ratio is found to exist. Noticeable as this is in the cases of these two provinces, when a like comparison is made with the eastern provinpe, a much greater discrepancy in the number of this group is seen. To so great an extent is this true that in a division of the continent into two longitudinal sections this family would enter as a very important factor of the problem, the number of Warblers found in the eastern province, ( its divisional line being drawn at about the one- hundredth meridian,) as compared with the western half, being nearly as two to one. No fewer than forty- two species of Warblers inhabit the eastern region. The greater proportion of these occur in the extreme eastern part, being there distributed to the several avian faunas that have been marked out from along its son them border to its northernmost limits. The greatest number of species occur towards its northern portions, especially in the Alleghanian and Canadian faunas as restricted ; those whose habitat is northern, visit, of course, the lower faunas in their migrations. As localities to the westward are noted it will be fouud that the number of species diminishes, and several birds are lost sight of ere reaching the Mississippi River. On its western edge the eastern province loses quite a large proportion of its characteristic species, no fewer than fourteen which occur along its eastern half, being absent in Kansas. A small percentage of eastern species still persist when the middle province is entered, some of them being found clear across the contiuent, forming, indeed, the larger percentage of the sylvicoiine avi- fauna. The following is a list of the eastern species that remain when the middle province is reached: 1. Helminthophaga celata. 2. JJendroica asstiva. 3. Geothlypis trichas. 4. Icteria virens. 5. Myiodioctes pusillus. G. Setophaga ruticilla. Helminthophaga ruficajrilla, Dendroica coronata, D. striata, D. maculosa, and Seiums no-reboracensis have all been found more or less numerously in Colorado and elsewhere withiu the limits of the middle region. They do not, however, breed there, but occur only as migrants in spring or fall as they pass to or from their northern summer hannts withiu the eastern province; hence they are not included in the above list. To those enumerated are to be added several species which are characteristic of the middle province, in so far at least as they are not fouud at all within the limits of the eastern; one or two of these occur, so far as known, only as migrants, their proper habitat being the Pacific province; several are confined to the extreme southern portion of the Rocky Mountains; . three only are confined to this proviuce. The additional species are : 7. Helminthophaga luciw. 8. Helminthophaga virginke. 9. Dendroica occidentals. 10. Dendroica townsendi. 11. Dtndroica nigrescens. 4 |