Part 47

HABITS

Along both coasts of Baja California southward from about latitude 27° N., and along the Pacific coast of Mexico from Sinaloa to Guatemala, where that curious tree, the red mangrove (Rhizophora mangle), bathes its feet in salt water along the shores of bays, estuaries, and tidal creeks, this handsome yellow warbler makes its permanent home. The red mangrove extends its growth on these muddy shores by sending its curving branches outward and downward to take root again in the mud, thus forming an almost impenetrable tangle of roots and branches in an ever-widening band extending outward from the dry land. Its dense, dark foliage forms a low, gloomy forest of branches in which this well-named warbler finds a secure retreat and to which it is almost exclusively confined. It has not always been easy to obtain in these tangles, for Brewster (1902) says that--

during January, February, and a part of March, 1887, Mr. Frazer repeatedly visited all the mangrove thickets that he could find near La Paz, and made every effort to secure a good series of these Warblers, but he took only eight in all and did not shoot more than a pair in any one day. He notes the bird as "rare," but adds that "its numbers Increased slightly in March." It cannot be very numerous here at any time, for the total area covered by its favorite mangroves is very limited. Indeed, the place where most of his specimens were obtained "comprises only about two acres, through which winds a small creek, fordable at low tide; but at high water everything is submerged up to the lower branches of the mangroves. I always found the birds working near the surface of the water on the stems of the mangroves or hopping about on the mud, but the males resorted to the tops of the bushes to sing. Their notes are similar in general character to those of the Yellow Warbler."

W. W. Brown was evidently more successful a little later in the season, for, in that same locality in May and June, he collected a large series of these beautiful birds for several American collections, mainly Col. John E. Thayer's. He wrote to Colonel Thayer (1909):

I found the Mangrove Warbler a rare bird, but my previous experience with this species in Panamá, the Pearl Islands, and in Yucatan is what made me successful. I learned its song and alarm note in 1893. The first morning I went into the mangrove swamps of La Paz I whistled the song of the Yucatan species and the birds answered me; this is the secret of my success, for the species is very secretive in its habits. I found it so difficult to get that I offered fifty cents apiece to the duck hunters and others, including the local taxidermist, but they all failed to get it! By covering eight miles of territory I generally managed to get four or five. Sometimes when I shot one It would fall in the mangroves, with a tide running fast. Under such conditions it generally took a long time to find it, and a great deal of cutting with the machete.

Referring to the form found in El Salvador, Dickey and van Rossem (1938) remark: "To add to the difficulties in the path of the collector, the brown and yellow plumage of the males blends perfectly with the dead or dying mangrove leaves which are kept in continual motion by the sea breeze."

Nesting.--Brown sent Colonel Thayer (1909) three nests of the mangrove warbler, only one of which contained a set of three eggs. Of this he says: "The nest with eggs is made (and the others resemble it very much) of light green fern down, cobwebs, and light-colored dried grasses, with a few white feathers plastered on the outside. It is beautifully lined with feathers. It is not so perfectly shaped or so well made as the Yellow Warbler's nest."

There are now six beautiful nests of this warbler in the Thayer collection in Cambridge, all collected by Brown near La Paz on dates ranging from May 15 to June 2; all were placed in the red mangroves, either on horizontal branches, mostly near the ends, or in forks; the heights from the ground or water varied from 2 feet to 10 feet. The largest and handsomest nest was 10 feet up on a horizontal branch; it is a very neat, compactly woven cup, made of soft, fine, light buff plant fibers, mixed with plant down, green moss that looks like down (probably the "light green fern down" referred to above or algae), a few gray lichens and many whitish flower clusters; it is lined with very fine fibers, apparently from the mangroves, and plenty of feathers; it measures externally 3 inches in diameter and 2-1/2 inches in height; the inner diameter at the top of the in-curved rim is 1-3/4 inches and the cup is near 2 inches deep. The smallest nest measures only 2-1/4 inches in outside diameter. The shallowest nest is only 1-1/2 inches high and 1-1/4 deep inside.

These nests are all works of art and quite distinctive; all the materials are smoothly and compactly felted, being tightly plastered together, as if glued on when wet. The light color and compactness suggest certain hummingbirds' nests. Most of the nests seem small for the size of the birds.

Eggs.--Three eggs seems to form the usual set for the mangrove warbler; in the Thayer series there are five sets of three and one set of two. Ed. N. Harrison (MS.) says that "it seems that one egg is a set as often as two." Most of the eggs in this series are ovate, but some are short ovate; they have only a very slight gloss. They are white or creamy white, speckled, spotted or blotched with shades of "mummy brown," "bone brown," "Prout's brown," or "clove brown," with undertones of "light mouse gray," "deep mouse gray," "Quaker drab," or "drab-gray." The browns are frequently so dark as to appear almost black, but some eggs are spotted with lighter shades, such as "cinnamon brown" and "snuff brown." On the more lightly marked types the most prominent markings are the grays, with only a few scattered brown spots. Often a loose wreath is formed around the large end, where the spots are usually concentrated.

The measurements of 32 eggs average 17.9 by 13.4 millimeters; the eggs showing the four extremes measure =19.5= by 13.2, 17.9 by =14.6=, =17.0= by 13.2, and 18.3 by =12.9= millimeters (Harris).

Plumages.--Although I have examined a large series of mangrove warblers, I have seen no downy young and no summer birds in juvenal plumage. But Dr. Chapman (1907) describes the young female as "above grayish olive-green, rump brighter; tail blackish, externally greenish, webs of all but central narrowly margined with yellow; wings and their coverts blackish, quills margined, coverts tipped with dull greenish; below whitish more or less washed or obscurely streaked with yellow, the under tail-coverts pale yellow."

Young males in the fall are much like adult females, but brighter in color and often with traces of chestnut on the head. Apparently young males wear this femalelike plumage all winter; young males in March show a variable amount of chestnut on the head and throat, and show further progress toward maturity during April, May, and June, indicating a first prenuptial molt. A specimen described by Brewster (1902) is apparently undergoing this molt. "It has the head dull chestnut, very pale and mixed with whitish on the throat, mottled with greenish on the crown; the jugulum, sides of the neck and the middle of the breast white with occasional small patches or single feathers of a pale yellow color and numerous fine, chestnut-rufous streaks on the breast; the remainder of the under parts pale primrose yellow mixed with whitish. The back, wings, and tail are nearly as in the adult female. The upper mandible is of the usual dusky horn color, but the basal half of the lower mandible of a pale flesh color. The plumage, generally, has a worn and faded appearance."

This would seem to indicate that the first prenuptial molt is quite extensive, and that young birds become nearly adult after their molt. Adults probably have a complete postnuptial molt sometimes during the summer, but the following descriptions indicate that the prenuptial molt of adults is less extensive. Ridgway (1885) describes the type male, taken December 16, 1882, as follows: "Head rich chestnut, lighter or more rufous on the throat. Upper parts olive-green, the wings dusky, with broad greenish yellow edgings; outer webs of rectrices dusky, edged with yellowish olive-green, the inner webs chiefly primrose-yellow. Lower parts bright gamboge-yellow, the jugulum and breast with a few very indistinct and mostly concealed streaks of chestnut-rufous." And of an adult female, taken December 29, 1882, he says: "Above grayish olive-green; wings grayish dusky, the feathers edged with olive-grayish; rectrices dusky, outer webs edged with olive-green, the inner with primrose yellow. Lower parts dull pale olive-yellowish."

From Dr. Chapman's (1907) descriptions of spring adults it appears that there is very little seasonal change. Male: "Head all around and throat reddish chestnut; back yellow olive-green, the rump brighter; inner webs of all but central tail feathers largely yellow; wings black margined with yellow; underparts, except throat, rich yellow faintly streaked with reddish brown." Female: "Above olive green, much darker and greener than ; tail black the two outer feathers with large yellow patches on the inner web near the tip; wings black margined with greenish yellow; below uniform pale, dull yellow."

Laurence M. Huey (1927), referring to the bird life of San Ignacio and Pond Lagoons, on the west coast of Baja California, states that mangrove warblers were found there--

in isolated pairs and gave evidence of early nesting by their singing and by the condition of the sex organs of the specimens collected. This warbler was one of the most interesting species observed. The song of the male was usually delivered from a hidden position amid the dense mangroves, though occasionally the bird was seen perched on a dry twig projecting above the level tops of the thicket. The song was pleasing in tone, and of good volume, suggesting that of the Yellow Warbler, but less shrill. Unlike the song of the Yellow Warbler, it was given with a steady rising inflection. The alarm note is a sharp chirp, audible at some distance even during a brisk wind. This note is uttered at intervals and always in the same tone, much as are the chipping notes of the Orange-crowned Warblers. In searching for food, Mangrove Warblers resemble others of the genus Dendroica in their habit of searching each leaf and stem with most careful scrutiny. At times, however, they were seen to launch forth into the air, in true "flycatcher" fashion, after small insects. These aerial sallies were seldom for a distance of over 10 feet, and the bird nearly always returned to the same perch from which it started.

Enemies.--The following remarks by Dickey and van Rossem (1938) about the El Salvador race of this species are of interest:

As the entire lives of these birds are spent in an environment which renders them immune from attack by the great majority of the predators which harass species inhabiting the land forest, one is at first inclined to be surprised at their relative scarcity. Raccoons (Procyon) are extremely common in the mangroves and were often found prowling through the branches at night. They, as well as carnivorous iguanas, undoubtedly take toll of many nests, but aside from these two it is difficult to conjecture what natural enemy operates to limit the mangrove warbler population. Certainly no "saturation point" has been reached, for pairs may be separated by as much as a mile even in the areas which appear most favorable.

DENDROICA MAGNOLIA (Wilson)

MAGNOLIA WARBLER

PLATES 26-28

HABITS

Wilson secured only two specimens of this pretty warbler, one of which was shot among some magnolia trees near Fort Adams, Miss. He gave it the scientific name Sylvia magnolia but called it the black and yellow warbler. This stood for many years as the common name. Nuttall, who had seen it only occasionally in Massachusetts, regarded it as rare. Audubon, on the other hand, found it quite common and even abundant in several places, as we now know it to be. His lively plate of this beautiful bird, one of his best, has always been a favorite of mine; and it seems to me that in the magnolia warbler, more than in any one of the many beautiful species of American wood warblers, are best combined daintiness of attire with pleasing combinations and contrasts of often brilliant colors. Particularly are these qualities apparent when this warbler is seen amongst the dark green firs and spruces of its summer home, where its brilliant array of colors are displayed to advantage as it flits about, sometimes within a few feet of us.

Spring.--From their winter quarters in Mexico and Central America, some magnolia warblers migrate straight across the Gulf of Mexico to the Gulf coast between Louisiana and western Florida; they seem to be accidental in Cuba and very rare anywhere in Florida. Another migration, probably of some importance, occurs along the coast of Texas from the mouth of the Rio Grande to Louisiana; I saw a few magnolia warblers in the great migration wave noted on an island in Galveston Bay on May 4, 1923. Professor Cooke (1904) remarks: "The dates of arrival of the magnolia warbler in spring furnish the best evidence yet available in support of the theory that birds migrating across the Gulf of Mexico do not always alight as soon as they reach the shore. The species is a common spring migrant from the Mississippi River to the Atlantic, between latitudes 37° and 39°. South of this district it becomes less and less common, except in the mountains, until in the Gulf States it is rare." It is significant that the earliest date of arrival at Atlanta, Ga., is the same as at the lower Rio Grande in Texas, April 20.

William Brewster (1877) writes:

The Black-and-Yellow Warbler arrives in Massachusetts from the South about the 15th of May. During the next two or three weeks they are abundant everywhere in congenial localities. Willow thickets near streams, ponds, and other damp places, suit them best, but it is also not unusual to find many in the upland woods, especially where young pines or other evergreens grow thickly. Their food at this season is exclusively insects, the larger part consisting of the numerous species of Diptera. The males sing freely, especially on warm bright mornings. They associate indifferently with all the migrating warblers, but not unfrequently I have found large flocks composed entirely of members of their own species, and in this way have seen at least fifty individuals collected in one small tract of woodland. By the first of June all excepting a few stragglers have left.

On its migration as well as on its breeding grounds the magnolia warbler seems to avoid the taller tree-tops and to prefer the lower levels in the forests and in the thickets along the borders of woodlands; it is sometimes seen in garden shrubbery and in orchards, where it adds a brilliant touch of color to the blossoming fruit trees. When it reaches its breeding haunts it prefers low hemlock thickets, or more especially, where these can be found, the dense thickets of small spruces or balsam firs that spring up thickly in old clearings, or grow profusely along the more open woodland paths; the density of the forest depths seems to be avoided in favor of the more open spaces.