The breeding biology of the water rail Rallus aquaticus in Britain and Ireland

The Water Rail Rallus aquaticus is a little studied bird thought to be in d ecline throughout Britain and Ireland. Particular uncertainty surrounds the breeding biology because nests are difficult to locate. In this paper the 80 nest record cards (1946-96) held by the British Trust for Ornithology we re analysed to describe the breeding biology in detail. Many of the cards c onsisted of a few observations only and rarely contained complete data on h atching and fledging success. Wafer Rail had a protracted breeding season ( March-June) and laid large and variable clutches (mode 8 eggs, range 5-13). There was circumstantial and actual evidence for two broods per season. Cl utch size increased with altitude and tended to be smaller early and late i n the breeding season.