126 BRITAIN'S BIRDS AND THEIR NESTS. 



It is not yet clear how the disease is spread, but 

 among probable explanations is the suggestion that healthy- 

 birds swallow food that birds in an advanced stage of 

 the disease could not swallow, and were therefore forced 

 to regurgitate. The possibility of the transmission of the 

 disease to other species of birds and to other animals, 

 including human beings, is an important but difficult and 

 much - disputed point. An important inquiry into the 

 whole circumstances of the Wood-Pigeon diphtheria is at 

 present in progress, and the results are awaited with 

 interest. A disease affecting the growing feathers and ulti- 

 mately rendering the bird incapable of flight also attacks 

 this species at times. 



THE STOCK=DOVE 



(Columba oenas). 



Plate 41. 



Although more local and altogether less abundant than 

 the preceding species, the Stock-Dove is a fairly common 

 bird throughout the greater part of the British Isles. 

 In many districts, however, it is not properly distin- 

 guished by the country-folk, but is confused with one or 

 other of its allies. It is very frequently misnamed the 

 ' Rock-Dove," and the confusion is increased by people who, 

 knowing its real name, imagine it is so called because the 

 species was the original 'stock' from which our domestic 

 Pigeons were derived. As a matter of fact, the Rock- 

 Dove is the ancestor of om- domestic birds, and the 

 epithet 'stock' has reference to the bird's habit of nesting 

 in the ' stocks ' of trees. 



The Stock-Dove may be distinguished from the Wood- 

 Pigeon by the absence of the characteristic white patches 



