On account of its great similarity of size, general appearance, and habitat, this rare British breeding species was long confounded by naturalists with the Reed Warbler.
The bird is greenish-olive on its upper parts, and lacks the rusty-red rump and sides of the commoner species. Its under parts are white, slightly tinged with yellowish-buff on the sides where the Reed Warbler is reddish buff. Its legs are pale flesh-brown in colour, whereas those of its relative are dark slaty-brown.
This species does not build its nest over water, whereas the one with which it has been confounded nearly always does so. The structure is composed of grass stems, and occasionally bits of moss intermixed on the outside with an inner lining of fine dead grass, and nearly always contains one or two black horsehairs. It is not so neatly finished as that of the Reed Warbler, and is generally suspended amongst nettles, Meadow Sweet, and Mugwood, the last plant appearing, where I have studied the species, to be first favourite.
The eggs, numbering from four to seven, are easily distinguished from those of the Reed Warbler by their lighter ground colour, which is greenish-white to greenish-blue clouded with underlying markings of grey and spotted with olive-brown.
It is as a singer of great sweetness and power, however, that the bird chiefly concerns us in this little work.
Last summer I spent several days in the West of England studying the species, and whilst I was lying hidden with my camera within three feet of a nest, had many opportunities of hearing the exquisite song of the male to perfection. Whilst the hen was sitting on the nest he frequently took up his station on a bramble spray just above and partly behind her, and regaled us both with the most wonderful programme of feathered music I have ever heard. As a mimic, the Marsh Warbler is unsurpassable.
MARSH WARBLER ON THE NEST.
Several times the specimen I listened to began his concert with the alarm cry of a Song Thrush, so loud and accurately rendered that I was completely deceived into thinking that I was listening to the notes of a disturbed member of that species. After a little pause he would reproduce the warbling notes of a Swallow, then the tut, tut, tut of a Blackbird, followed by the full, rich notes of the Nightingale. He could also reproduce the call note of a Common Partridge, and the sweet little song of a Linnet with equal fidelity. He always appeared to take great care not to mix his music, for, after finishing one piece, there was a noticeable pause before the commencement of another.