Red-backed Shrike (Lanius collurio) nest performance in a declining British population: a comparison with a stable population in Poland

摘要

We compare the breeding ecology of Red-backed Shrike Lanius collurio prior to its effective extinction (in 1990) as a breeding bird in the UK with that of a stable population in southwestern Poland. We use breeding performance data derived from the UK and Polish Nest Record Schemes. Although the clutch size in the UK was slightly smaller than in Poland (4.52 +/- 0.09 and 4.79 +/- 0.11, respectively), brood sizes of UK nests were significantly larger (3.21 +/- 0.14 v.s. 2.21 +/- 0.23) than those from Poland. These data do not suggest that poor breeding performance drove the population decline in the UK. We argue that other evidence suggests that egg collecting and delayed phenology may have contributed to the extinction, although we have been unable to assess the influence of other possible factors such as predation and post-fledging survival.