Causes of the decline in partridge populations and effect of the insecticide dimethoate on chick mortality.

Abstract

The decline of the grey partridge has been investigated during 23 years in Sussex, using an integrated approach based on long-term monitoring of mortality at various stages in the life cycle, of chick foods, pesticide use and farming practices. Further study was based on computer simulation modelling and field experiments. A quantified hypothesis about the cause of the decline was formulated and tested by experiments.

The population decline was mainly caused by a shortage of insect food for chicks caused by herbicides (indirectly) and insecticides (directly). As a result chick mortality rates have increased. A second effect is - for a given density - a large increase in nest predation. This has been caused by a reduction in traditional predation control activities of gamekeepers, itself largely caused by the lowered chick production rates eroding the value of predation control. It is considered that the future EC policy extensification offers a chance to reverse the decline of the partridge, but that the present policy set-aside is harmful in this respect.