Estimating brood production and chick survival rates of grey partridges: an evaluaton.
Potts (1986. The Partridge: Pesticides. Predation and Conservation. Collins. London) described a method of estimating the parameters quantifying breeding success for the grey partridge Perdix perdix on the basis of autumn counts. We review his method and evaluate its accuracy against situations where the true values are known: an intensive study at Damerham, U.K. (1947-1959), two small radio-tracking studies in the U.K. (early 1980s), and a large-scale radio-tracking study in France (1995-1997). The method performed well when compared with the British data, which had been obtained from sites with low predator pressure. In France, estimated chick survival rates were also accurate after correcting for differences in brood size at hatching, even with sample sizes as low as two. The method proved not suitable to estimate hen survival rates in areas with a high density of harriers Circus. Elsewhere, the accuracy of the estimation of hen survival rates was generally good (making allowance for additional mortality caused by wearing radio transmitters), although it deteriorated for chick survival rates below 0.3.