64 EGYPTIAN BIRDS 



sides or by the river's edge, but if any of my readers 

 will endeavour to build up a nest with such mud 

 against an upright wall, they will attempt an all 

 but impossible task, for as the curve begins to grow 

 outwards it will with its own weight fall away from 

 the wall. What is it, then, that the Swallows and 

 Martins do to make their nests adhere ? If you 

 examine an old last year's nest and try and break 

 the outer shell, you will find it very tough consider- 

 ing the material it is made of, and the toughening 

 matter is a secretion of saliva. In the case of some 

 species of Swallows this secretion is so great that 

 the whole of the nest is made of that substance 

 alone, with the lining of a few feathers. And it is 

 this nest, cleaned of all foreign matter which is the 

 base of the much-esteemed delicacy known as bird- 

 nest soup. Few who have partaken of this luxury 

 are perhaps aware that it is simply solidified saliva. 

 Of Martins there are two — the House-Martin 

 and the Sand-Martin, both birds common to Great 

 Britain. Of the latter, literally thousands and 

 thousands will be seen nesting in colonies in the 

 mud banks by all who go up and down the river ; 

 restless and cheerful, they are one of the welcome 

 sights of the Nile trip, and often for miles at a 

 stretch the whole banks are honeycombed with 



