1306 
REPORT OF THE CHIEF OF ENGINEERS. 
The Western Orange-crowned Warbler, (Helminthophaga celata var. lutescens ,) which 
is distinguished varietally, as it occurs on the west coast, mainly by its brighter col¬ 
oration, is here decidedly paler, though still approximating more closely to this than 
to the interior and eastern form, H. celata. The same is true of Myiodioctes jmsillus var. 
pileolatus as compared w T ith M. pusillus. The Song Sparrow of this region, though re¬ 
ferable to the Pacific type, (Melospiza melodia var. heermanni ,) yet very distinctly ap¬ 
proaches thed/. 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, (Tasserella 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. 
scliistacca. 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 ( Sylvicolida',) 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 province, 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 prob¬ 
lem, the number of Warblers found in the eastern province, (its divisional line being 
drawn at about the one-liundredth 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, beiog there 
distributed to the several avian faunas that have been marked out from along its south¬ 
ern 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 found 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 character¬ 
istic 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 continent, forming, indeed, the 
larger percentage of the sylvicoline avi-fauna. 
The following is a list of the eastern species that remain when the middle province 
is reached : 
1. Helminthophaga celata. 
2. Dendroica a’Stiva. 
3. Geothlypis trichas. 
4. Icteria virens. 
5. Myiodioctes pusillus. 
G. Setophaga ruticilla. 
Helminthophaga ruficapilla, Dendroica coronata, D. striata, D. maculosa, and Seiurus no- 
vthoracensis have all been found more or less numerously in Colorado and elsewhere 
within 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 haunts 
within 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 found 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 por¬ 
tion of the Rocky Mountains; three only are confined to this province. 
The additional species are : 
7. Helminthophaga lucice. 
8. Helminthophaga xnrginiae. 
9. Dendroica occidentalis. 
10. Dendroica townsendi. 
11. Dendroica nigrescens. 
