Abstract
CapsuleTwo populations of the Eastern Great Reed Warblers, one close to settlements and one far away, differed mainly in nest losses which were higher at the latter site. Aims To compare the breeding ecology of two Japanese populations, and with breeding data from Polish sites. Methods We studied two sites in 1996. The Seimei site comprises a natural reed-bed (Phragmites australis) (2.0 ha) c. 2 km from residential areas. The Sakura site occurs as smaller reed-bed (0.8 ha) close to residential areas. Field study comprised mainly nest searching and nest monitoring. Results Breeding density, nest height, number of stems supporting nest, clutch size and brood size were not significantly different between sites. The proportion of nests built on reed stems standing in the water (60%) was significantly higher at the Seimei site (P < 0.001), and the warblers in this habitat experienced significantly higher nesting failure (P < 0.05). Predation was a principal cause of failure at both sites. Significantly more nests suffered from predation at Seimei (53%) than at Sakura (16%). Breeding density was higher at both sites compared with European populations but it fell within ranges of other Japanese populations. Mean first-egg date of first brood does not differ between our sites and Polish ones. Conclusion The differences between the two Japanese populations and between Japanese and Polish populations were relatively small and were seen mainly in nest losses, breeding density and proportion of nests built over water.
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