272 THE USEFUL BIRDS 



the relations between the Lory and the fungus of the citrus 

 tree : — 



" Mr. J. G. 0. Tepper, of Adelaide, has sho^^^l me," writes 

 Mr. M'Alpine, " how the destruction of honey-eating birds 

 may affect the sooty mould of citrus trees. It may be 

 mentioned that it appears to have been practically absent 

 when nature was less disorganized by man, and for a very 

 simple reason. Being due to the sugary exudations of scale- 

 insects, &c., coating the trees, its abundance depends upon 

 that of its producers, and this upon the reduction of the 

 sugar-loving brush-tongued Parrakeets and other birds, \\hich 

 formerly abounded so greatly. These I have often observed 

 busy in the early morning among the foliage of gums, &c., 

 upon which honey-dew appeared. Later in the day the ants 

 occupied these in overwhelming numbers, and drove the birds 

 away, protecting the insects and cleaning the fohage. 



" The complex relation seems to be in the following form : — 



" 1. — The scale or other insects are used directly to attract 

 the ants by their sweet secretions. 



«' 2. — The ants, like a standing army, protect the foliage 

 against the attacks of leaf-eating animals. 



" 3. — The abundance of honey-eating birds is necessary to 

 keep the scale or other insects within reasonable bounds. 



" 4. — The reduction of these birds by man temds to favour 

 the increase of the scale-insects and their produce. 



" 5. — The scale and other insects now get the upper hand, 

 and the ants, protecting the insects, also favour their increase. 



" 6^ — The consequence is superabundance of honey-dew, 

 and this is taken advantage of by the germs of the fungus to 

 spread and multiply. 



" Thus the destruction of the honey-eating birds has brought 

 about an increase of the honey-dew and of the sooty-mould, 

 which lives upon it, so that it is not only insectivorous birds 

 which ought to be protected for the benefit of the grower." 



