92 THE WOODPECKERS 



But first, in how many ways is it possible for 

 a bird to use his tail as a prop? He may of 

 course hold it open or closed ; and the open tail 

 may be held in a single plane, " spread flat/' as 

 we say ; or curved up at the edges, like a crow 

 blackbird's ; or curved down at the edges. And 

 the closed tail may be held in a single plane ; 

 or, by dropping each pair of feathers a little, in 

 several planes. Thus we see there are five posi- 

 tions in which each shape may be held against 

 the cylinder of paper. Try each one against it, 

 holding it first in the open positions and then 

 after folding the paper like a bird's tail with 

 the outer feathers underneath, in the closed po- 

 sitions. The size of the model tree-trunk and 

 the shape you cut your curves will make the re- 

 sults vary a little, but you will be surprised to 

 observe, if your models are not too small, how 

 many times you will get the same answers. 

 Note the number and position of the pairs that 

 touch : 



Forked end. Round end. 



