The decline of the corncrake <em>Crex crex</em> in Britain and Ireland in relation to habitat change.

Censuses of singing male corncrakes Crex crex (L.) on agricultural land in seven sample areas of Britain and Ireland in 1988 and 1991 indicated that a century-long decline in numbers was continuing. Areas differed in the magnitude of the population change during the 3-year period. Changes ranged from a 4% increase to a 70% decrease. Vegetation surveys were carried out in 1988 and 1991 at sites that were occupied by corncrakes in 1988. A logistic regression model, developed in a previous paper, which describes differences in vegetation between sites that corncrakes had continued or ceased to occupy between 1978/79 and 1988, was applied to the 1988 and 1991 vegetation data in order to estimate area-specific changes in habitat suitability over the 3-year period. Variation in the rate of change of corncrake numbers among geographical areas was well explained both by the absolute value of the habitat suitability index in 1991 and the change in the index between 1988 and 1991. Changes in corncrake numbers were better explained by the habitat suitability index than by any of the individual vegetation cover variables used in its calculation. Declines in corncrake numbers were generally associated with reductions in the area of hay-meadows, but increases in short pasture and grassland dominated by Juncus spp. also contributed to declines in corncrake habitat suitability in some areas. [ABSTRACT FROM AUTHOR]