Demography and the decline of the grey partridge Perdix perdix in France

1. Bird populations can be efficiently managed only if the demographic mechanisms that cause change are correctly understood. Here we illustrate the demographic variables causing decline among grey partridge Perdix perdix populations in France by comparing populations that show contrasting trends. The analysis combined a field survey at 10 contrasting sites during 3 years, modelling and statistical analyses; survival rates and reproductive success were estimated through the largest-ever radio-tracking study of hens, while density was estimated through counts. 2. Population viability analyses showed that, in France, north-western populations of grey partridge were healthy whereas south-eastern populations were declining. 3. Elasticity analyses accounting for environmental stochasticity indicated that the survival rate during shooting, over winter and at the time of the first nesting attempt were the most important demographic influences on population growth rate. The hatching rate, covey size at hatching of first clutches and chick survival rate were secondary. The contribution of replacement clutches to population change was low. 4. Multiple regression showed that hen survival during the first nesting attempt explained 33% of the variability in the population growth rate across populations. The shooting pressure increased with the health of the population. 5. Improving survival rate during winter and the first nesting attempt was not sufficient for recovery in a declining population. It was also necessary to increase simultaneously the hatching rate of first clutches and chick survival rate to produce a stable population that could sustain shooting. 6. Low hen survival rates, in particular during the breeding period, explain the recent decline of grey partridge populations in some regions of France. However, the recovery of populations will need a simultaneous improvement of several demographic parameters.