284 The Lesser Birds of the Sierra 
lighter coloured varieties of the Swallow's. Considering the 
abundance of this species it is curious how rarely its nest is 
found in accessible spots. After four years of disappointments, | 
watched a pair enter a rocky cavern below a waterfall in a deep 
water-worn ravine. To get at this nest I had to be lowered some 
15 ft. to the pool below the fall and since we had no ropes, this had 
to be done with the aid of our fazas (known to Anglo-Indians as 
cummerbunds) knotted together. | then swam across the pool and 
entered the cavern, in the roof of which was a nest with four eggs. 
Sad to relate, so obsessed was I with the idea that this Crag Martin 
built a nest similar to our House Martin and laid white eggs like 
it and the Sand Martin that I imagined the nest and eggs I had 
found belonged to the Common Swallow, of which there were some 
also about, and so abandoned my prize! My disgust upon learning, 
some months later, that I had actually had the eggs I longed for in 
my grasp may be best imagined. Owing to the fact that I am 
rarely in the sierras at the season when the Crag Martins lay, 
many years passed before | had another opportunity of getting 
this nest and it was not until rgo01 that I at last succeeded! 
Truly a little knowledge is a very dangerous thing, at any rate 
as regards the identification of eggs! 
Besides the Crag Martin, the House Martin (Chelzdon urbica) 
nests in abundance in certain parts of the sierra. 
Without doubt the most conspicuous and best known of all the 
cliff-haunting birds is the Blue Rock Thrush (Petrocossyphus cyanus), 
known to the Spaniards as So/ztavzo from its habit of sitting alone, 
perched on the summit of some crag or, if near inhabited places, on 
the top of some commanding building. 1 believe I am correct in 
saying that it was this bird that David had in his mind when he 
described himself as watching, ‘“‘as a sparrow alone upon the house- 
top,” and further that some learned ornithologists attempted, but 
without success, to have this apparent error amended in the Revised 
Version. 
