In the UK, the corncrake is listed in the Red list of birds of high conservation concern because of major population declines both historically and recently.
Solutions to stop decline
Corncrakes are threatened Europe-wide due to major declines through much of its range. Research on corncrake population declines suggested that effective conservation measures should include increasing the area of suitable tall vegetation, ensuring that sufficient tall vegetation is present in spring and autumn as well as in mid-summer, delaying the date of mowing and using mowing methods that allow flightless chicks to escape.
Simulation models of corncrake breeding show that delaying the date of mowing can increase breeding success markedly and mowing from the inside of the field outwards (the reverse of the usual practice), or using another method that allows chicks to escape, increases the proportion of chicks that survive mowing. These methods are termed Corncrake Friendly Mowing (CFM).
Up to about 60 per cent of chicks are killed by usual mowing practices because they are reluctant to escape across parts of the field that are already cut. Chicks may be at risk from mowing several times before they can fly as successive fields are mowed. Alternative mowing methods can reduce this risk substantially.
Reserve management for corncrakes
In the 1990s several nature reserves were acquired by the RSPB and managed mainly for corncrakes and the management of suitable habitat on some other reserves has been made more favourable. RSPB reserves now hold about 8 per cent of the national population.
Within these reserves, the area of spring and autumn cover for corncrakes has been increased by fencing off the margins and corners of hay and silage meadows and establishing stands of suitable vegetation. The area of hay, silage and autumn grazed pasture has been increased. The impact of hay and silage mowing on breeding success has been reduced by delaying mowing until August and using CFM.
A programme of payments to farmers to delay mowing until August and to use CFM was first implemented in Scotland by RSPB in 1992 (Williams et al. 1997). This has since been translated into Government-run schemes. Payments are available to encourage changes in the mowing of meadows within 250 m of the singing place of a male corncrake.
Once widespread throughout the UK, its population declined catastrophically during the 20th century due to the mechanisation of mowing and earlier mowing of grass crops. By the 1990s it bred only in the Hebrides and Orkney in Scotland.
Since 1992, conservation measures to benefit corncrakes have been implemented on a large scale, principally through agri-environment schemes (AES), during which time the corncrake population has partially recovered.
Two measures have been designed to benefit corncrakes. Early and Late Cover provides suitable tall vegetation throughout the breeding season, especially at the start and end of the season when grazed or cut vegetation in grass fields is too short for the birds.
Delayed mowing of hay or silage crops delays the date of mowing to reduce the overlap between the breeding and mowing seasons, and involves the adoption of corncrake-friendly mowing techniques to reduce the loss of chicks to mowing.
Both ESAs now encourage farmers to delay mowing until after 31 July and the Argyll Islands ESA also requests the provision and safeguarding of tall vegetation suitable for corncrakes in spring and autumn.
Calling male corncrake numbers in the UK were estimated to be just 480 in 1993. Since then numbers have recovered substantially in their core area and there was an estimated 1,140 males in 2008.
All surveys of distribution and censuses between the late 19th century and 1993 recorded a progressive decline in the national population and range with the average rate of population decline between 1988 and 1993 being 3.5 per cent per year. In contrast, the population increased between 1993 and 1998 by an average of 4.2 per cent per year.
The coincidence of the recent corncrake population increase with the development of the conservation programme from 1992 onwards suggests the possibility of cause and effect, but a longer period of implementation and monitoring is required to see whether the population recovery is sustained.