DOMED OR ROOFED NESTS 239 



{Chelidon iirhica). The nest of the bird furnishes 

 another very interesting example of a changed method 

 of building within historic time. Before the dawn of 

 human architecture in England this Martin attached 

 its nests to rocks, and possibly to big trees, but when 

 masonry appeared the bird gradually took possession 

 of the sites with which we are all so familiar to-day. 

 House Martins now nest indiscriminately upon cliffs 

 and buildings, when on the latter some spot with a 

 projecting ledge or cornice being selected similar to 

 the sites chosen on cliffs where a natural prominence 

 furnishes the all-necessary protection. The nest is 

 somewhat like a half basin in shape, more conical in 

 some than in others, the rather wide entrance hole 

 generally being close to the rim, between it and the 

 sheltering projection above, and either at the front or 

 on one side. The shell of the nest is made of little 

 pellets of mud, built on piece by piece sometimes with 

 bits of straw intermixed to give it better adhesive 

 properties. The interior of this mud shell is then 

 lined with dry grass and feathers. The House Martin 

 generally begins at the bottom of the cup, working 

 upwards and outwards towards the sheltering pro- 

 minence, plastering on each little ball of mud either 

 whilst clinging outside or standing inside the structure. 

 These birds are gregarious, and in some places every 

 available bit of wall or cliff is occupied by a nest. Rows 

 of these may often be seen under copings or eaves, but 

 on cliffs they are of course placed less regularly, 



