46 BIRDS' NESTS 



gent groups — became nestless. That it is an excep- 

 tion to the general habit of birds is unquestionable — 

 a deviation from almost universal custom, rather 

 than a retention of an archaic trait. Possibly the 

 habit may have arisen through individuals accidentally 

 depositing their eggs on the ground before any nest 

 had been prepared for them, just as we often find 

 nest-building species do in our own time. I have 

 known the Starling especially to drop its eggs very 

 frequently about the fields, the Song-Thrush and 

 Blackbird, Bunting and Robin occasionally, but never 

 to attempt to incubate them, however, in such a novel 

 position. It is somewhat significant, too, that the 

 most thorough nestleas species lay but a very small 

 number of eggs for a sitting — from one to two or 

 three. If the eggs were as readily hatched under 

 nestless conditions, and possibly received additional 

 safety by the absence of a perhaps conspicuous nest, 

 then we can understand how natural selection would 

 preserve such new conditions of incubation and the 

 habit consequently have a tendency to increase. 



From the absolutely nestless birds we now pass 

 to a consideration of those species which we have 

 designated " Annexers " ; that is to say, birds that do 

 not under any circumstances make a nest for them- 

 selves, but select the disused or unoccupied home of 

 some other species in which to lay their eggs and 

 bring up their young. So far as is known, this 

 singular habit, with few exceptions, occurs only in 



