Some breeding statistics of Reed and Sedge Warblers

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Abstract
The BTO [British Trust for Ornithology] nest records cards of reed [Acrocephalus scirpaceus] and sedge warblers [A. schoenobaenus] are analyzed. Reed warblers had a later and more protracted breeding season. In both species, clutch and brood sizes fell during the season. The modal clutch sizes were not the most productive of fledged young, but subsequent survival rates of reed warblers showed that this was influenced by brood size and the time of hatching. Circumstances and causes of failure were described, and a probability method was used to study failure rates of nests and their seasonal variations. From this it was possible to calculate the expected outcome of breeding starting at any time, and the patterns differed markedly between the species. Hypothetical populations were modeled to calculate the breeding productivity. Several questions requiring further investivation are listed. More attention should be given to probability methods of studying failure rates of nests.