NOX-INDIGENOUS BRITISH BIRDS, ^7 



it travels in flocks of varying size, the companies dis- 

 banding and dispersing over a wide area as the summer 

 haunts are reached. The nest of this species is made in 

 a great variety of situations, but almost invariably in a 

 covered site and well concealed. It is made under a 

 mass of rock, or amongst heaps of loose stones, some- 

 times in crevices of rocks, or in holes of ruined masonry, 

 in the walls of houses, or in trees. Exceptionally it is 

 made under the shelter of a bush, or beneath a large 

 tuft of drooping grass. The same variation is to be 

 remarked in the materials. In some districts roots, 

 moss, dry grass, and stalks of plants form the exterior, 

 lined with hair or feathers, fine roots and grass ; in 

 others, roots and dry grass and a few dead leaves are 

 the only materials. In wild regions the lining of hair 

 and feathers is rarely employed. The nest is open, cup- 

 shaped, and rather loosely put together. The bird is a 

 close sitter, but generally shows little anxiety when 

 flushed from the nest unless the eggs are hatched. 



Range of egg colouration and measurement : 

 The eggs of the Rock Thrush are four or five in number. 

 They are a pale clear turquoise blue, sometimes faintly 

 speckled round the larger end with pale brown, but very 

 often entirely spotless. Frequently one Qgg only in a 

 clutch will be marked, a fact which seems to show that 

 the colour glands in this species have become almost 

 obsolete. Average measurement, ro inch in length by 

 76 inch in breadth. Incubation is performed by both 

 sexes, but the duration of the period is unknown. 



Diagnostic characters : The size and colour (espe- 

 cially when spotted) of the eggs, combined with the 

 position of the nest, serve to distinguish them from those 

 of other Palxarctic species, except from those of the 

 Blue Rock Thrush, from which they cannot be separated. 

 They require careful identification. 



