The characters by which this species may be distinguished from _S. strepera_ may be briefly stated as follows:—
Although the colour of the upper portion of the plumage in both is a uniform olive-brown, _S. palustris_ is yellower. It is a somewhat longer bird, with a shorter and broader bill; a buffy-white line, extending from the base of the bill over the eye, is clearly defined. In _strepera_ this line is so faint as to be scarcely discernible. Mr. Yarrell, indeed, considered it to be absent in _strepera_; but, from this circumstance, and from the fact of his describing the legs of this species as pale-brown, it may be inferred that he had before him, and figured, a young bird.
The first primary in the wing of both is very short, quite rudimentary, in fact; while the third in each is the longest in the wing. In _palustris_ the second primary is equal to the fourth; while in _strepera_ the second is equal to the fifth. It is doubtful whether this can be invariably relied upon, for the length of feathers, even in the same species, will sometimes vary considerably, through age, moult, or accident.
The readiest means of distinguishing the two birds at a glance will be by the colour of the legs and toes. In living or freshly-killed specimens it will be observed that the tarsi and feet of _strepera_ are of a slaty-brown colour, while in _palustris_ the same parts are flesh-colour. In dried skins, the former turns to hair-brown; the latter to yellowish-brown. The tarsus of _palustris_, moreover, is rather longer and stouter than that of its congener. From this it appears that Mr. Gould in his “Birds of Great Britain” has figured _palustris_ for _strepera_.
Dr. Bree, in his “Birds of Europe,” has unfortunately figured _palustris_ with slate-coloured legs and feet, which quite alters its appearance, although he has been careful in the text to describe the colour correctly.
The tail in _palustris_ is less rounded than in _strepera_; the outer tail-feather in the former being not so short as in the latter.
The measurements of the two species, taken from skins, are as follows:—
_S. strepera_ 5·3 in. 0·5½ 2·7 0·8 _S. palustris_ 5·5 in. 0·5 2·5 0·9
The nests and eggs differ as much as do the birds themselves.
