The Correct Cover For Corncrakes

Abstract from the Journal of Applied Ecology
22nd July 1996

One of the most endangered species, globally and within Britain and Ireland, is the Corncrake. Its range in Britain and Ireland has dwindled for more than a century and the numbers have plummeted until last year - when there was a modest increase. Efforts of conservation organisations, together with the crofters and other farmers, have concentrated on methods of mowing and the time of mowing hay fields.

Writing in the Journal of Applied Ecology (33, 237-248), Rhys Green, of the Royal Society for the Protection of Birds has tried to discover exactly what these choosy birds need. The survey relied on the census in 1988 to pinpoint the 218 1-km squares that were surveyed. All had at least one singing Corncrake in that year. (Those lucky birders who have heard a Corncrake 'sing' will realise that this is euphemism which would place the late, great Schnozzle Durante up there with Pavarotti. The 'song' is a monotonous 'crex, crex, crex' repeated over and over again. Guess the scientific name? CREX CREX!)

The amount of tall vegetation (Iris, reed and other things like nettles), the crops and other land use were all assessed and the mowing dates of the hay or silage were also recorded. As is usually done, Rhys then set about modelling what factors were affecting the Corncrakes. As some readers of Bird-On! will realise this is a horribly complicated process.

The result was to show that the amount of tall vegetation - Iris and reed - and grass taller than 20 cm in summer were positively associated with the population density of the Corncrakes. But this was only true if the mean date of mowing was late July or later. This is hardly surprising as the poor bird's chicks would routinely be mown to death otherwise.

In fact all 22 1-km squares with more than 2 ha (that is 2% of the area of the square) of tall vegetation, more than 10 ha of grass taller than 20 cm in summer and a mean mowing date of 22 July or later held singing Corncrakes. In these squares each male had, on average 1.4 ha of tall vegetation and 7.6 ha of tall grass.

The strategy for protecting this species was confirmed. Neither hay meadows nor tall vegetation will do the trick without the right management of the hay mowing. And timing is crucial as well as the newfangled idea of mowing from the centre to scatter the Corncrakes rather than concentrate them for a coup de grace when the final cut is taken.