264 ODD HOURS WITH NATURE 



dow, old mills with the rafters conveniently ex- 

 posed they are all caves to the swallow, giving 

 the needed elements of a roof overhead, with con- 

 venient irregularities for the attachment of nests 

 where cats and other creeping quadrupeds cannot 

 approach. And as the interior of a building is 

 a cave to the swallow, the wall of a building is a, 

 cliff to the house -martin, and the overhang of 

 the roof or the corner of an elevated window repre- 

 sents the ledges. 



There can be no doubt that the power of 

 recognizing that a made interior is as good as a 

 cave, and that a wall is as good as a cliff, has 

 proved of the greatest utility to these two members 

 of the swallow family. Over the greater part of 

 Britain natural cliffs are of rare occurrence, and 

 natural caves, even if we include great hollows 

 in trees, are rarer still. If, therefore, the house- 

 martin and the swallow were confined to them 

 for nesting sites, both species would be of ex- 

 ceedingly local distribution. As it is, they occur 

 in practically every district of the country, except 

 in the high altitudes. It may be said, then, that 

 the human settlement of the country has been the 

 occasion of a great expansion of the numbers of 

 the swallow tribes one point to set on the credit 

 side of our account with nature and against the bill 

 of extermination for which our responsibility cannot 

 be denied. 



