THE DECLINE OF THE CORNCRAKE CREX-CREX IN BRITAIN AND IRELAND IN RELATION TO HABITAT

1. Censuses of singing male corncrakes Crex crex (L.) in 1978/79 and 1988 on agricultural land in Britain and Ireland indicated that numbers had, on average, declined by 30% during this time period in areas for which the two censuses were comparable. This represents the continuation of a long-term decline. However, population changes differed among areas, ranging from a 72% decline to a 15% increase. 2. Areas in which the greatest declines had taken place tended to be those in which a high proportion of sites which held corncrakes in 1978/79 had ceased to be occupied by 1988. 3. Sites were identified that were occupied by corncrakes in 1978/79 and that had ceased or continued to be occupied by singing males in 1988. Vegetation surveys were carried out in 1988 at all such sites that could be located with precision. A logistic regression model was used to describe differences in vegetation between sites that corncrakes had continued or ceased to occupy. Sites which continued to be occupied had greater cover of Iris pseudacorus, Phalaris arundinacea and Phragmites australis and hay meadow and less of short dry pasture and wet pasture dominated by Juncus spp. and Carex spp. 4. There were highly significant differences between geographical areas in the proportion of previously occupied sites at which corncrakes continued to occur. A significant part of this variation was explicable in terms of the modelled effects of differences in vegetation cover. Geographical variations in population change were also correlated with an index of habitat suitability based on the logistic regression model. 5. It is suggested that changes in grassland management have contributed to the continuing decline in the corncrake populations in Britain and Ireland.