Although often taken to comprehend every species of warbler, Professor Newton has recently shown[5] that the genus Sylvia of Latham should be restricted to the group of fruit-eating warblers next to be described, and that the generic term which has priority for the willow wren group is Phylloscopus of Boie.

From its larger size, brighter colour, and finer song, the Wood Warbler deserves to be first noticed; and the first step should be to distinguish it from its congeners. Perhaps none of the small insectivorous birds have been more confounded one with another than have the members of this group, not only by observers of the living birds, but by naturalists with skins of each before them. Taking the three species which annually visit us—i. e., the Wood Warbler, the Willow Warbler, and the Chiff-chaff—it will be found on comparison that they differ in size as follows—

Not only is the Wood Warbler the largest of the three, but it has comparatively the longest wings and the longest legs. The wings, when closed, cover three-fourths of the tail. In the Willow Wren, under the same circumstances, less than half the tail is hidden. The Chiff-chaff’s wing is shorter again. In my edition of White’s “Selborne,” founded upon that of Bennett, 1875, pp. 56, 57, will be found a long footnote on the subject, with woodcuts illustrating the comparative form of the wing in these three birds. Mr. Blake-Knox, in “The Zoologist” for 1866, p. 300, has pointed to the second quill-feather, depicted in a sketch accompanying his communication, as being an unfailing mark of distinction.[6] When we reflect, however, upon the variation which is found to exist in the length of feathers, owing to the age of the bird, moult, or accident, too much stress ought not to be laid upon this as a character. At the same time there is no doubt that, taken in connection with other details, it will often assist the determination of a species. After examining a large series of these birds, I have come to the conclusion that, as regards the wings, the following formulÆ may be relied on: Wood Warbler, 2nd=4th; 3rd and 4th with outer webs sloped off towards the extremity. Willow Warbler, 2nd=6th; 3rd, 4th, and 5th sloped off. Chiff-chaff, 2nd=7th; 3rd, 4th, 5th, and 6th sloped off.

The Wood Warbler is much greener on the back and whiter on the under parts than either of its congeners, and has a well-defined superciliary streak of sulphur-yellow, which, in the Willow Wren, is much shorter and paler. The legs of the Wood Warbler and Willow Wren are brownish flesh-colour, while those of the Chiff-chaff are dark brown. After the first moult, the young of all three species are much yellower in colour than their parents. Hence the mistake which Vieillot made in describing the young of P. trochilus as a distinct species under the name of flaviventris.

Although the majority of the SylviidÆ are fruit-eaters, the species now under consideration are almost entirely insectivorous;[7] they are also more strictly arboreal in their habits, and as regards the character of their nests, they differ remarkably from other members of the SylviidÆ in building domed nests on or near the ground, instead of cup-shaped nests at a distance from it. The Yellow-billed Chiff-chaff—or Icterine Warbler, as it should now be called[8]—however, forms an exception to the rule, as will be seen later. As these little birds make their appearance at a season when caterpillars and destructive larvÆ begin to be troublesome, the good they do in ridding the young leaves and buds of these pests is incalculable. I have watched a Willow Wren picking the green aphis off a standard rose-tree, and have been as much astonished at the quantity which it consumed as at the rapidity of the consumption. The Wood Warbler is not nearly so sociable as either the Willow Warbler or the Chiff-chaff. It keeps to the tops of trees in woods and plantations, and seldom comes into gardens; hence it is not so often seen. Although not rare, it is somewhat local, and in the British Islands, it appears, is confined exclusively to England and the south of Scotland. Mr. Thompson has included it with hesitation amongst the birds of Ireland; for although the description given to him of certain birds and eggs seemed to apply to this species, it was stated that the nest which contained the eggs was lined with feathers. Now, the Willow Wren invariably makes use of feathers for this purpose, but the Wood Warbler does not. The nest of the latter is composed entirely of dry grass and leaves, occasionally mixed with a little moss; and although I have sometimes found horsehair inside, I do not remember to have seen or heard of an instance in which any feathers were employed. The eggs, five or six in number, are white, closely freckled over with reddish brown.

Mr. Blake-Knox, a well-known naturalist, resident in the county of Dublin, says (“Zoologist,” 1866, p. 300), “I tried very hard this year to add the Wood Wren to our Dublin avifauna, and though I killed some dozens of snowy-white-bellied Willow Wrens, they were all the common Sylvia trochilus. That the bird is Irish I am sure, for I have heard it. Should an Irish ornithologist see this, will he try for it, if he should live in a wooded district, such as the counties Wicklow and Wexford? I am sure it is neglected for want of a certain distinction.” Since this note was published, the Wood Wren has actually been obtained in Ireland, a specimen having been shot in the county of Fermanagh by Sir Victor Brooke, and preserved by him in June, 1870. Another was obtained the same year at Glen Druid in the county of Dublin, as reported by Mr. Blake-Knox. Both Sir William Jardine and Macgillivray have referred to the Wood Warbler being found northward to the middle districts of Scotland, a circumstance which appears to have been overlooked by Mr. Yarrell, since he says (vol. i. p. 349, 3rd edit.), “I am not aware of any record of its appearance in Scotland.” This statement, however, has been rectified in the fourth edition of this standard work by Professor Newton, who remarks: “In Scotland it is known to breed regularly in the counties of Dumfries, Wigton, Lanark and Berwick, the Lothians and Perthshire, and occasionally in those of Roxburgh, Selkirk, Renfrew and Stirling.” Mr. A. G. More, in an article “On the Distribution of Birds in Great Britain during the Nesting Season,” published in the “Ibis” for 1865, observes (p. 26), that the Wood Warbler “in Scotland ranges further north than the Chiff-chaff, having been observed by the Duke of Argyle in Argyleshire and at Balmoral.”

According to Mr. Robert Gray, of Glasgow, it has been observed in Inverness and Aberdeenshire, and Mr. Edwards has found it in Banffshire.

Beyond the British Islands the Wood Warbler is found throughout Europe, though rare in the north, and it extends eastward to Siberia and southward to Algeria, Egypt and Abyssinia. It arrives in this country generally about the middle of April, and leaves again in September.