The period of incubation commences early in the spring, each brood (of which there are always two, sometimes three, in the course of the season) consisting of four or five eggs. When first fledged the nestlings are unable to fly, and run over the ground exactly after the fashion of young mice. Whilst the little family is in this helpless condition, the parents are constantly in a state of great excitement and anxiety; their cry of admonition or warning is then to be heard incessantly; even when the young are sufficiently advanced to perch upon the branches, the same cautious watchfulness against approaching danger is maintained, and we have often amused ourselves by observing the precipitation with which the whole group of little Blackheads disappear as the obedient nestlings hurry to some safe shelter within the bush or tree, at the first signal from their vigilant parents. Such of these birds as inhabit mountain ranges do not migrate; in Spain they live at an altitude of 3,000 feet above the sea, and even when the snow begins to fall they merely come into the valleys below, and never wander to any great distance from their native haunts.
The TREE WARBLERS (Phylloscopi) constitute a family whose members are met with throughout the world. With the exception of one group, all are small, slender, delicately-shaped birds, with comparatively long wings, in which the third, fourth, and fifth quills usually exceed the rest in length. The tail is of moderate size, either quite straight or slightly incised at the extremity, and these tarsi are of medium height. The beak is awl-shaped, slender, rather flat at its base, and in some instances somewhat broader than it is high. The plumage is soft, and very uniform in colour; it is usually of a pale green or brown on the back, and yellowish on the under side. All the species with which we are acquainted principally frequent the summits of trees, but come down occasionally to seek their insect food upon the rushes, or in the fields of corn; they seldom consume berries, unless compelled to do so by hunger. All are active and restless, and display great agility, both among the branches and when running over the surface of the ground; their powers of flight are also good, their voice always agreeable, and their senses well and sometimes highly developed. Such as inhabit Southern Europe, Asia, and Africa do not migrate, whilst those in milder latitudes leave their native lands late in the autumn, and return to them again in the early spring. These latter species generally breed twice during the summer, and lay from four to seven delicate white or pale rose-red eggs, marked with dark spots. The nests of all are constructed with the utmost care.
THE FIELD TREE WARBLER, OR WILLOW WREN.
The FIELD TREE WARBLER, or WILLOW WREN (Phyllopneuste Trochilus), is a slenderly-formed bird with long wings, in which the third and fourth quill exceeds the rest in length. The tail is of moderate size, and slightly incised at its extremity; the beak is delicate, broad at its base, and compressed at its tip. The lax plumage is of an olive green upon the upper parts of the body, and white on the under side, the breast being tinged with greyish yellow; a yellowish-white stripe passes over the eyes, and the cheek stripes are deep grey; the quills and tail-feathers are grey, edged with green, and the lower wing-covers light yellow; the eye is brown; the beak and legs grey. After the moulting season the under side becomes a pale yellow. This species is four inches and eleven lines long, and seven inches four lines broad; both wing and tail measure about two inches. The sexes are alike in colour; the young are greyish green above and yellowish-white on the throat; the rest of the under side is white, tinted with yellow.
THE FIELD TREE WARBLER, OR WILLOW WREN (Phyllopneuste Trochilus).
The Field Tree Warblers inhabit the whole continent of Europe, a large portion of Northern Africa, and some parts of North America. During their migrations they also occasionally visit India and Northern Africa. For the most part, however, such as quit Northern and Central Europe for the winter do not wander farther than its more southern countries. These birds alike frequent highlands and lowlands, and usually pass the summer months in disporting themselves about the leafy summits of lofty trees. In autumn, on the contrary, they come down into the brushwood and beds of reeds or rushes, or, in Southern Europe, alight in the fields of maize in quest of food; dense forests they appear almost entirely to avoid. The song of this species is pleasing and flute-like; its chief beauty, however, consists in the delicacy of intonation and rapid swelling and sinking of sound in which the male indulges, as he sits with drooping wing, inflated throat, and raised crest, upon a projecting branch, or flutters rapidly from bough to bough, in order to attract the attention of his intended mate; at such times the female also utters a faint twittering kind of song. Like the Tree Warblers, these birds are particularly active among the foliage; they do not creep in the quiet mouse-like manner above described, but flutter about with a constant brisk agitation of the tail that cannot fail to betray their presence to an observant eye. While perched the body is usually held erect, but is kept somewhat bowed down as the bird hops upon the ground; this latter mode of progression is accomplished with some difficulty, each long hop, or rather leap, being followed by a succession of rapid gesticulations with the head before another effort is made. Their flight is capable of being long sustained, but is somewhat inelegant, and appears unsteady, as it is usually undulating and carried on by a series of very irregular efforts. The same restless activity is also observable in the conduct of these birds towards all their feathered companions; the slightest injury or annoyance is resented with much fury, and even the sportive exercises in which they frequently indulge usually terminate with a series of violent flappings and peckings given on either side, rather in downright earnest than in play. The nest is carefully concealed in a hollow in the ground or in the trunk of some tree, and built entirely by the female, who commences her operations by hacking at the hole or aperture till it is of the requisite depth. The utmost caution is displayed by the anxious mother to prevent the discovery of her future abode. For this reason she seldom works except during the early morning, and at other times never remains near the scene of her operations. The nest itself is cone-shaped, with thick walls, in one side of which a hole is left for entrance; dry leaves, stalks, moss, and grass are employed for the exterior, while the interior is snugly lined with feathers, those of partridges being usually preferred. From five to seven eggs form a brood; these are laid about May, and are oval in shape, smooth, glossy, and white, more or less spotted with light red. During the period of incubation the female displays much anxiety for the safety of her eggs, and even when alarmed will not leave them until she is forcibly removed. At mid-day her mate takes his place on the nest for an hour or two, but with this exception gives her no assistance; both parents, however, combine to rear and protect the nestlings, and endeavour to attract the attention of any intruder on their privacy and divert it to themselves, by hurrying to a distance and uttering cries of distress. The young are fledged by the end of May, and a second brood is produced in June.