OUR FEATHERED ENGINEERS. 73 



are the House Martins and the Swallows. The 

 former birds, as is well known, build their nests 

 under the eaves of houses, in window-frames, 

 beneath the copings of viaducts, in doorways, and 

 even on the bare cliffs, both inland and on the 

 coast. As in the Thrushes, the nests undergo 

 several stages. The masonry part of the struc- 

 ture is first completed. The Martins, as soon as 

 nest-building commences, may be seen alighting 

 on the margins of ponds and streams, or even on 

 the roads, to pick up little bits of mud. These 

 pellets, one by one, are attached to the selected 

 site on the wall or cliff until sufficient foundation 

 is laid, when the real work of constructing the 

 outer shell of the nest begins. Backwards and 

 forwards the little masons fly, to and from the 

 pools or roads, bringing each time a fresh piece of 

 mud, which is carefully stuck upon the nest like 

 so many bricks. The Martins only do a little at 

 a time, leaving the work to set and become firmly 

 cemented together, and to the wall, ere going on 

 again. Gradually the shell is formed, neatly 

 attached at the back, and sometimes overhead, to 

 the supporting masonry, course succeeding course, 

 a small aperture being left at the top for ingress. 

 This semi-globular nest of mud is then lined with 

 dry grass and feathers, and all is ready for the 

 tiny white eggs. During dry seasons the Martins 

 often have considerable difficulty in getting mud 

 plastic enough for their purpose, and will fly long 

 distances to obtain this material. Then, again, 



