Breeding biology of the Song Thrush Turdus philomelos in an island population

Capsule: Breeding characteristics were explained by agricultural intensification, climate, latitude and insular syndrome. Aims: To describe the timing of breeding, clutch size and number of nestlings hatched and fledged, assess nesting success and investigate growth development of nestlings in Song Thrush. Methods: Nests were monitored intensively in County Cork, southwest Ireland, and extensively countrywide by volunteers. The number of nesting attempts, location, surrounding habitat, nest height above ground and sea level, date of first egg, nesting stage, clutch size, number of chicks hatched and fledged and causes of nest failure, daily nest survival, fledglings per attempt (FPA), reproductive output per attempt (ROA) and seasonal productivity were recorded. Results: Data collected from 100 nests during 2001-03 were available for analysis. The breeding season extended from mid-March to late June. Only 3% of nests represented third broods. Mean clutch size was 4.1 (±0.62), number of hatchlings was 3.7 (±0.92) and number of fledglings was 3.7 (±0.89). Clutch size and brood size, at hatching and fledging, significantly differed with month, year, nesting attempt, latitude and altitude. FPA was calculated as 0.75 and ROA as 1.13. Seasonal productivity was calculated as 2.7 young fledged from 3.7 nesting attempts. Daily nest survival rates were: egg stage 0.9362 (±0.0126), incubation stage 0.9505 (±0.0121) and nestling stage 0.9609 (±0.0096). First broods had higher, though not significantly, daily failure rates than second broods during all nest stages. Weather did not have any significant effects on nest survival or outcome. Most nest failures were due to predation at both egg and chick stages. Avian predation was more common than mammalian. Conclusion: Differences in breeding biology characteristics between Ireland and other European countries may be explained by agricultural intensification, climate, latitude and insular syndrome. The data presented provide a baseline for future monitoring and may also help in conservation measures in areas of decline.