Breeding biology and breeding success of the Lesser Grey Shrike Lanius minor in a stable and dense population

The Lesser Grey Shrike Lanius minor is highly endangered throughout Europe, having declined markedly in abundance and range. Long-term changes in clim ate and agricultural practices have been identified as the main reasons for its decline. To determine which factors influence short-term changes in br eeding success, we examined several aspects of its breeding biology. Our in vestigation revealed that our study area bears a large and stable populatio n of this species. In 1996 and 1997, we recorded 84 and 77 breeding pairs i n an area of 20 km(2), with an average of 4.20 and 3.85 pairs/km(2) respect ively. Data on breeding density, clutch size and fledging success from 1989 to 1997 (excluding 1992) indicate a stable breeding population with a cons tant high breeding success. Reproductive success declined through the seaso n, mainly through seasonal variation in clutch size rather than chick morta lity. However, breeding success was generally high (69% and 79% of the nest s produced chicks), with low hatching failure and few nest losses. The main cause of breeding failure was nest predation (at least 50% of nest losses) , mainly by magpies (at least 66% of depredated nests). Although in this po pulation the Lesser Grey Shrike tends to aggregate in clusters, breeding de nsity had no obvious effect on breeding success and nest predation.