NATURAL AGENCIES.

Forest and Bird, Issue 21, 1 July 1930, Page 19

NATURAL AGENCIES.

Of the several natural agencies influencing insect-develop-ment, birds and insect-feeding insects can be brought more or less under human control and utilized for the purpose of holding in check insects injurious to forests. As has already been shown, the native birds are intimately associated with the forests, and are responsible in part for keeping the insect balance. The great reduction of these birds, through altered environment, has been responsible for the increase of several insects. There is ample evidence to show that the native insectivorous birds are essential to the success of the indigenous forests, and in many cases to the development of exotic trees; and the preservation and increase of native birds should be an outstanding feature of forestdevelopment. The utility of the bird factor is well illustrated in an account from Germany (1) : In two forests separated by a road, one suffered from complete defoliation by moth-caterpillars, while the other, which was an established bird sanctuary, was undamaged, and the swarms of moths that migrated to it from the infested area were devoured by the flocks of birds.— " Forest and Timber Insects of New Zealand, Bulletin II.” by Dr. David Miller, B.Sc., F.E.S.