282 The Lesser Birds of the Sierra 
foremost comes one of the smallest of European birds, the Common 
Wren, which inhabits the wildest and most desolate hills and 
shares with the big Vultures the deep caverns hundreds of feet 
above the sea level. Wherever suitable sites are to be found, for 
example among the innumerable ‘ pockets” with which the roofs 
of the sandstone caverns are pitted, there may the Wren be 
reckoned to breed, making its snug nest of the materials nearest 
at hand. 
One of the things that most deeply impress my mind when, 
after a hard struggle, I have gained the summit of some great 
lide 
overhead or sweep past hundreds of feet below, but never a sound 
do they utter. The same with Eagles or with the startled Rock 
Doves which dash out of the caverns hard by. Suddenly close 
alongside, the silence is broken by the shrill cheery song of the 
cliff, is the absolute silence around. The Vultures may 
oO 
cos) 
Wren! No height seems to be too great for this undefeated little 
bird. At the very summit of a great cliff, whose base lay in the 
cork woods over 500 ft. below, | have found a Wren’s nest built 
ina hole in the same cavern and in close proximity to that of the 
huge Griffon Vulture. In this instance the Wren had constructed 
the external part of the nest almost entirely from the Vultures’ 
feathers, the lanceolate ones from the ruff forming a feature in the 
architecture, whilst the lining was composed of the snowy white 
fleecy down which forms the underclothing of the Griffon. 
One of the most widely distributed among the smaller birds of 
the sierra is the beautiful little Crag Martin (Cotyle rupestris), which 
to the uninitiated bears a likeness to our own Sand Martin (Cotyde 
riparia). Some of these birds winter in southern Spain sheltering 
among the deep ravines low down in the sierras where they are 
protected from wind and weather. Their numbers are largely 
increased during February. They build a nest of cemented mud, 
cup-shaped similar to that of our Common Swallow (/Zzvezdo rustica) 
