A series of eight nests now before me vary considerably in size, compactness, manner of construction, and in the materials used. The largest two measure 4 inches and 33⁄4 inches, respectively, in outside diameter, and the smallest ones measure from 23⁄4 to 3 inches. The inner diameter seems to be more constant, varying from 13⁄4 to 2 inches. All of my nests are shallow, hardly more than an inch deep internally in most cases. Some of them are fairly well made, but most of them are very flimsy and more or less transparent. The neatest nests have the sides and rims well built up with dry grass or weed stems of varying degrees of fineness and density. In some there is no grass, but the sides are well made of the very finest hemlock or larch twigs interwoven with fine, red, fruiting stems of mosses and many fine, black rootlets; they are often slightly decorated or camouflaged with a few weed blossoms or bits of wool or plant down. The lining of black rootlets is present in these and in all other nests of the magnolia warbler that I have seen; it seems to be characteristic of the species and will distinguish the nests from those of other warblers. This jet-black lining forms a fine background against which the handsome eggs are shown in striking contrast.
Miss Stanwood gives in her notes the following account of nest building: “The birds fly with much jolly chattering through the trees and examine any nesting sites that appear desirable. The dainty female, after fitting her little body into many spaces among the twigs, finds one that is entirely adapted to her prospective domicile, and the birds proceed to fashion a basketlike frame of long, fine potentilla or cinquefoil runners, or culms of fine hay. These they fasten to the twigs and needles around the selected space with spiders’ web, or tent caterpillar silk, leaving the long ends free. Around the top of the basketlike frame on the interior is laid a culm of hay in the form of an imperfect circle, which is secured to the frame with spiders’ silk; many of the long ends are then turned down within, or crumpled into the space for the foundation of the superstructure. In the frame is fashioned the cradle, which is symmetrical and cup-shaped on the inside, but may be formed like the bowl of a spoon on the outside, according to the space which it is designed to fill. The preferred lining materials appear to be a jet-black, hair-like vegetable fibre, and horsehair, but on occasion, the dull orange setae of the birdwheat moss, or the brown fruit stems of maples are used for this purpose.
“Both twittering birds bring the materials while it is damp, if possible, and place it, but being very timid, they work little while an observer is near. At such times the birds come silently, one at a time, deposit the bit of cinquefoil or hair-like fibre hurriedly, the female who is oftentimes less timid than the male, doing most of the modelling, turning around and around in the tiny dwelling and shaping it with her breast. Two birds that I timed carefully spent 4 days building their habitation, and another pair 6 days in doing the same work. The amount of time occupied by the task is determined by the abundance or scarcity of materials and the weather; continuous, heavy, cold and retard the work greatly.”
Eggs.—Four eggs almost always form a full set for the magnolia warbler, but sometimes there are only three and occasionally five. They vary in shape from ovate to short ovate, or rarely to elongate ovate, and are only slightly glossy. The ground color is white or creamy white and in some instances greenish white. Their markings vary considerably, some being very lightly speckled, while others are boldly spotted, blotched or clouded with “buffy brown,” “cinnamon-brown,” “Mars brown,” “Prout’s brown,” “mummy brown,” “Brussels brown,” “chestnut,” “auburn,” or “tawny-olive,” with occasional scrawls of “bay” or black, and with undertones of “vinaceous-drab,” “deep brownish drab,” or “Quaker drab.” There is a tendency for the markings to be concentrated at the large end, where they often form a wreath, or sometimes a solid cap. Many interesting effects are found on the boldly marked eggs, where the large brown blotches are superimposed on the drab undertones. The measurements of 50 eggs average 16.3 by 12.3 millimeters; the eggs showing the four extremes measure 17.9 by 13.2, 15.0 by 12.0, and 15.8 by 11.6 millimeters (Harris).
Young.—The period of incubation for the magnolia warbler is said, by different observers, to be 11, 12, or 13 days, and it is evidently performed by the female only. Miss Stanwood tells me that incubation sometimes begins after the second egg is laid. One egg is laid each day until the set is complete. The young remain in the nest from 8 to 10 days, usually the latter. The eyes of the young are opening on the third or fourth day. On the sixth day, the feathers are breaking the sheaths, and by the eighth or ninth day the young are well feathered. The female does all the brooding of the young, of which Miss Stanwood writes in her notes:
“At first the mother bird covered the young much of the time, as the infant birds were fragile and the weather was cold and damp. Every few minutes the brooding bird moved back on the nest far enough to feed the nestlings regurgitated or digested food, and to cleanse the nest of biting pests such as ants, which might endanger the lives of the baby birds. The father bird sang gaily, far away and near at hand, throughout the long summer day. When he came to the nest with food, he flirted his tail, fluttered his wings, quivered all over and twittered very prettily to his mate, who responded in like manner.
“He presented his first tender moths and juicy caterpillars to the mother bird, who ate part of them, but the remainder she crushed and mixed with digestive juices in her mouth and placed well down the throats of the baby birds.
“The little ones were not many hours old before the male insisted on presenting to them a few tidbits himself; and in a few days the parents fed the young almost exclusively on fresh insect food, which grew larger and tougher as the days went by.”
She mentions two attempts of the parent birds to draw her away from their young: “Once I accidentally flushed a brooding magnolia. The bird disappeared into the underbrush, but soon attracted my attention to herself by calling from the top of a second-growth fir, a few yards from where her precious secret was concealed. Then she fell from branch to branch, striking the boughs with a thud, like a dead weight, and dragged an apparently helpless leg or wing over the ground, but always away from where her treasures were hidden. On another occasion, when I visited a family of magnolias that were quite ready to fly, the little ones spilled over the side of the cradle into the surrounding grasses and ferns. Both parent birds, with spread wings and tail, tumbled from all the seedlings in the vicinity and trailed around in widening circles, calling piteously. At last the male bird poised himself in air on fluttering wings between me and a callow youngster, but the moment I lessened the distance between us he vanished.”