BIRDS. 



177 



game-preservation, mice and voles rapidly increase in enormous 

 numbers, especially in dry mild seasons, and may inflict serious 

 damage on plantations. When small plantations are attacked 

 a surrounding trench about 18 inches deep can be dug, wider 

 below than above, into which the voles fall and cannot climb 

 out again. But during plagues (as in 1864-67 and 1891-92), 

 large numbers can be killed by laying oatmeal poisoned with 

 barium carbonate or phosphorus paste in drain-tiles throughout 

 the plantations, although the attacks generally continue till the 

 balance of nature is restored by increase of the birds and other 

 animals which prey on mice and voles. 



Birds are on the whole far more beneficial in preying on mice, 

 voles, and insects, and on snails and slugs in nurseries, than 

 injurious in eating seed and damaging plants, although % in 

 nurseries the seed-beds may often need protection by moistening 

 the seed and rolling it in red-lead powder, or by covering the 

 seed-beds with a wire-net framework. As regards their general 

 importance to the forester, birds may be classified as follows : 



