Part 38

SENNETT'S OLIVE-BACKED WARBLER

HABITS

This northern race of a wide-ranging species is represented by a number of allied races in Central and South America. From its range in northeastern Mexico it rarely crosses our border into the valley of the lower Rio Grande in southeastern Texas. For its introduction into our fauna and for most of our knowledge of its habits we are indebted to George B. Sennett (1878 and 1879) and to Dr. James C. Merrill (1878). The discovery of the bird in Texas in 1877 is thus described by Mr. Sennett:

On April 20th, soon after reaching Hidalgo, I was directed up the river some four miles by road, and there shot the first three specimens of this new species. On May 3d, another was shot among the mesquite timber of the old resaca, within a mile of town.

On May 8th, another was shot in a dense forest about half a mile from where the first three were obtained. Several more were seen; in fact, they were more abundant than any other Warbler. * * * All of the specimens obtained are males, and I remember of seeing none in pairs. They were seen usually in little groups of three or four. They are by no means shy, but frequenting, as they do, the woods, cannot be readily seen.

He visited the locality again the following year and says in his report (1879):

It is truly a bird of the forest, and delights to be in the upper branches of the tallest trees. The song of the male is almost continuous as it flies about, and is so clear that it can be heard at a long distance and readily distinguished from all other birds. By its notes we could locate the bird, and this accounts for our securing so many more males than females. Were it not for its song, I doubt if we would have taken many, owing to their diminutive size and habit of frequenting the tops of the forest-trees. As it was, by only taking such as came in our way, we shot over twenty specimens, and could have taken any number more had we set out for them alone. In feeding habits I could see nothing different from our familiar Blue Yellow-back, P. americana.

Dr. Merrill (1878) says of its haunts: "Arrives about the third week in March, and passes the summer among thick woods and near the edges of lagoons where there is Spanish moss." We found Sennett's warbler fairly common around Brownsville, especially on the edges of the resacas, partially dry old river beds where the trees, mostly small mesquites, are more or less draped with Usnea and suggest the places where we would look for parula warblers in the north.

In appearance and behavior they were strikingly reminiscent of our northern friends. Sutton and Pettingill (1942) found this warbler up to 2,000 feet elevation in southwestern Tamaulipas, in full song on March 14, and a pair copulating on March 20.

Nesting.--Dr. Merrill sent to Mr. Sennett (1878) the following description of a nest he found near Brownsville after Mr. Sennett left: "My nest of Parula was taken July 5th, about five miles from here. It was placed in a small thin bunch of hanging moss, about ten feet from the ground, in a thicket; was simply hollowed out of the moss, of which it was entirely composed, with the exception of three or four horsehairs; entrance on side; contained three young about half fledged. Parents very bold, but thinking they were americana I did not shoot them."

The next year, his Mexican guide brought him a nest and a broken egg, which Mr. Sennett (1879) describes as follows:

The nest is exceedingly interesting and beautiful. It is made in a gray mistletoe-like orchid, an air-plant very common on the Rio Grande, which establishes itself on the small branches of trees, and varies in size up to eight or ten inches in diameter. This one is six inches long by four and one-half inches wide, quite firm in texture, and was fastened some ten feet from the ground, to the end of a drooping branch of a brazil-tree in open woodland. The nest is constructed very simply, being formed by parting the gray leaves of the orchid and digging into its centre from the side, a cavity some two inches in diameter being made, with an opening of one and one-quarter inches. The bottom and sides are lined pretty well up with short cotton wood fibres, forming a fine matting for the eggs to rest upon. A firmer and more secure nest is seldom seen, although so easily made. I imagine a day would complete one, and certainly but little time need be wasted in selecting a site, for thousands of orchids stand out on the partially dead branches on trees with little foliage. That they build also in the hanging trusses of Spanish moss, so abundant everywhere, is true, the young before referred to being found in a nest in one.

There are two nests of Sennett's warbler in the Thayer collection in Cambridge. One of these was taken for F. B. Armstrong in Tamaulipas, Mexico, on July 5, 1911, and held three eggs. It is described as a "nest of hair in bunch of growing moss hanging from limb of cypress tree in river bottom," 8 feet up; it is built right into the Tillandsia and is made almost wholly of black and white cattle hair. The other, with a set of four eggs, was taken by James Johnson near Saltillo, Mexico, on May 27, 1906. It is described by the collector as "dug and hollowed in a bunch of pipestem mosses." It is a compact little nest made of very fine rootlets, very fine grasses, shreds of the brown inner bark of the palmetto or palm, and some weed blossoms; it is lined with finer shreds, a little plant down, and a few feathers. Externally it measures 2-1/2 inches in diameter and 2 inches in height; the inside diameter is about 1-1/2 inches; and the depth of the cup about 1-1/4 inches.

Eggs.--Either 3 or 4 eggs seem to constitute the full set, as far as we now know, for Sennett's warbler. The 7 eggs in the Thayer collection vary from ovate to short ovate, and have only a slight lustre. They are white or creamy white and are speckled and spotted with shades of "wood brown," "cinnamon-brown," or "Brussels brown," with underlying spots of "pale brownish drab." On some eggs the markings run to much darker browns, such as "auburn" and "chestnut," and on these the drab spottings are frequently lacking. Usually a loose wreath is formed where the spots are concentrated at the large end, but occasionally they are distributed nearly evenly over the entire surface. The measurements of 36 eggs average 16.3 by 12.2 millimeters; the eggs showing the four extremes measure =19.0= by =13.7= and =15.0= by =11.3= millimeters (Harris).

Plumages.--Young Sennett's warblers that I have examined are uniform grayish olive above, inclining to olive-green on the back; the black lores and cheeks are lacking; the median wing coverts are narrowly tipped with whitish, and the greater coverts more broadly so; the chin is pale yellow; the chest and upper breast are shaded with pale gray and centrally tinged yellowish; the abdomen is dull white; and the sides and flanks are shaded with pale olive-grayish. I have not seen enough material to trace subsequent molts and plumages, which doubtless parallel those of the parula warbler.

Food.--We have no definite information about the food of Sennett's warbler, but Clarence F. Smith has sent me the following note: "The only laboratory report available on the food of the species pertains specifically to a South American subspecies of the pitiayumi group. The stomach contents were reported to consist of remains of hymenopterous insects and two-winged flies (Zotta, 1932)."

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Nothing further seems to have appeared in print regarding the habits of this warbler. It is much like the well-known parula warbler in appearance and behavior, but can be recognized in the field by the conspicuous black lores and cheeks and by the complete absence of any pectoral band.

DISTRIBUTION

Range.--The species ranges from southern Texas to northern Argentina and Uruguay. The race occurring in the United States is found in southern Texas and northeastern Mexico.

Breeding range.--Sennett's olive-backed warbler breeds =north= to northeastern Coahuila (Sabinas); and southern Texas (Hidalgo, Harlingen, and Point Isabel). =East= to southern Texas (Point Isabel and Brownsville); and southeastern Tamaulipas (Altamira and Tampico). =South= to southern Tamaulipas (Tampico); and southern San Luis Potosí (Valles). =West= to eastern San Luis Potosí (Valles); and eastern Coahuila (Cerro de la Silla and Sabinas).

Winter range.--While probably not a sedentary form, its winter range very nearly coincides with its breeding range. It has been found in winter from Brownsville, Tex., to northern Hidalgo (Jacala).

Egg dates.--Texas: 6 records, April 28 to May 30; 4 records, May 2 to 12, indicating the height of the season.

Mexico: 2 records, May 27 and July 5.

PARULA GRAYSONI Ridgway

SOCORRO WARBLER

HABITS

The Socorro warbler is closely related to Sennett's warbler and other races of pitiayumi but is accepted as a distinct species. It differs from nigrilora in having gray, instead of black, lores and cheeks, and in having much less white on the inner webs of the outer rectrices. It was supposed to be confined to Socorro Island, one of the Revillagigedo group, about 250 miles southwest of the southern tip of Baja California. It was added to our fauna by Chester C. Lamb (1925), who states: