3o6 BIRD WATCHING 



principle, and the exercise of ordinary intelligence, the 

 last stage of lining the cup with grass may finally cease. 

 It has ceased with the thrush, but, with the thrush, 

 there has been a still further process of change, for it 

 no longer plasters its nest with mud, but with decaying 

 wood and with cow-dung. Assuming the ancestors of 

 the bird to have once used mud, and lined the interior, 

 as does the blackbird, there does not seem to me to 

 be any great difficulty in explaining this change. The 

 blackbirds that I watched building their nest, always, 

 when the proper period arrived, flew to a certain part 

 of a little muddy dyke (it is in a land of dykes that 

 I reside) some little way from the plantation in which 

 the nest was situated, and there, lying flat behind tufts 

 and tussocks of reeds and grass, I watched them take 

 their mud as I have described — the female, that is to 

 say, but a husband much interested in seeing a baby 

 carried would deserve half the credit of carrying it. 

 Now, much nearer, probably, than this specially-re- 

 sorted-to dyke was some decayed tree or tree-trunk, 

 whilst over the fields which it intersected and which ad- 

 joined the plantation, cows or oxen sometimes grazed. 

 Here, again, a change in the working material might 

 prove of advantage, and when once a bird had become 

 a plasterer, intelligence, and also haste, might lead it 

 to use whatever came first to hand. Bees will carry 

 oatmeal instead of pollen if the former be put in their 

 way, and birds may be credited with equal adaptability. 

 After watching blackbirds building, and examining 

 the nest in its various stages of construction, I think it 

 much more likely that the thrush has passed through, 

 and then discarded, a final stage of thatching the nest, 

 than that it has stopped short at the stage of plaster- 



