Today's blog is a long-read by Professor Rhys Green, Department of Zoology, University of Cambridge on the conservation of corncrake in Scotland.
The corncrake is an iconic bird for an unfortunate reason. It is one of the best-known examples of a bird species that was formerly widespread in Britain and Ireland, but rapidly disappeared from most areas and continued to decline in numbers quite quickly thereafter.
The RSPB began to count corncrakes in the 1970s, started to study them in the 1980s and began an intensive programme of conservation action in the 1990s, underpinned by problem-solving research, in partnership with government agencies, crofters and farmers.
An article, “Corn Crake Conservation”, just published in the November edition of the journal British Birds, describes what was done to save the corncrake and why it was done, and also asks whether it has worked. The answer is that the conservation programme worked remarkably well in reducing negative effects of farm management on corncrake breeding success which allowed the Scottish population to increase for twenty years after decades of continuous decline towards expected national extinction.
However, numbers have started to decline again in the last five years, probably because of changes in a government programme which has been supporting conservation actions by farmers and crofters.
A mated pair of corncrakes. Soon the female (right) will be left to care for the eggs and chicks on her own © Andy Hay (rspb-images.com)
History of the corncrake’s decline
Victorian naturalists knew the corncrake well. It bred in all parts of Britain and Ireland and although it hid in hay meadows and other tall vegetation, the loud crek-crek song of the territorial males, delivered throughout the night, made its presence obvious. So naturalists immediately noticed when corncrakes began to vanish at the end of the 19th and beginning of the 20th centuries.
In the 1930s, a pioneering study of the decline by amateur ornithologist Tony Norris revealed a striking pattern. Local naturalists, who corresponded with Norris, recorded that corncrakes had disappeared soon after the introduction of horse-drawn machines to mow hay, which had previously been scythed by hand. The machines came into use at different times in different areas and, in each area, the corncrakes vanished soon after.
Norris noted that corncrake nests and chicks were destroyed during mowing. Chicks seemed to be especially vulnerable because machine mowing from the edge of the hayfield inwards caused them to be trapped inside an ever-decreasing and short-lived refuge of uncut grass.
Corncrakes had vanished from southern England and Wales by the 1940s. They survived in parts of the north of mainland Britain until the 1970s, but in the 1980s and 1990s the mainland populations dwindled away leaving significant numbers only in the northern and western islands of Scotland. National counts of singing male corncrakes began in the 1970s and showed that the population was still declining continuously even there. The species seemed to be destined to disappear.
Corncrake adult wing stretching in Isle of Tiree, Scotland © John Bowler (rspb-images.com)
Designing the conservation programme
By glueing miniature radio-tags onto their backs, RSPB biologists tracked the secretive corncrakes in the 1980s and 1990s to find out more about their ecology and the factors that affect where they can live and how successfully they breed. This technology was new at the time and was essential to trace the movements of a species that stays hidden in tall vegetation as much as possible.
It was found that corncrakes choose particular kinds of vegetation for nesting, chick-rearing and feeding. It must be tall enough to conceal them from enemies, but the ideal is an umbrella-like vegetation structure which allows the birds to access the soil surface to find their invertebrate food whilst remaining hidden. Mixtures of yellow flag iris, cow parsley and nettles at least 20 cm tall are among the most suitable types of cover.
Vegetation of this kind is scarce in April and May when corncrakes set up territories and start to breed because of grazing by livestock, but fencing off small areas can spare enough to attract birds to settle. The most important discovery from radio-tracking was that most female corncrakes, which nest on the ground and care for their eggs and chicks without help from the male, rear two broods of chicks each year in quick succession.
Nettles grown as cover for corncrakes on Oronsay RSPB reserve, Argyll © Andy Hay (rspb-images.com)
Most of the first broods are reared in and near the restricted areas of tall vegetation present in spring, but most of the second broods are in grassy fields that are cut for hay and silage, in which the grass only becomes tall enough to hide the birds and their nests and young in June. The females need to rear young from both of these broods to prevent the population from declining, but mowing of hay and silage was occurring during the rearing of most of the second broods.
Surveys of singing male corncrakes and weekly mapping of grass mowing in the 1980s and 1990s showed that numbers were declining very rapidly in areas with early mowing in June and July and only remaining stable where the average mowing date was in August.
Detailed studies of timing of breeding and the rates at which nests and chicks were destroyed by mowing indicated that corncrake populations could only recover if mowing was done later and using methods such as cutting from the centre of the field outwards to allow chicks to escape into neighbouring areas (Corncrake-Friendly Mowing). In addition, the creation of areas of suitable tall vegetation habitat in spring was needed to attract territorial males into areas where the mowing methods would allow their mates to breed safely.
A corncrake nest located by radio-tracking the female. The first egg of the ten-egg clutch had been laid early that morning © Charlie Self
Results of the conservation programme
To begin with, crofters and farmers made aware of the corncrake’s plight by local RSPB staff, agreed to delay mowing of hay and silage and adopt Corncrake-Friendly Mowing voluntarily, especially on the Isle of Tiree. Soon, this was followed up by a scheme in which the RSPB and Scottish Natural Heritage (now re-named NatureScot) offered payments for these conservation measures.
Government agriculture agencies then joined in with an agri-environment programme which included similar measures to protect corncrake nests and chicks from mowing. These were offered and adopted throughout the species’ range in Scotland on such a scale that well over than half of the breeding population was benefitting by the mid-1990s.
The numbers of singing male corncrakes in most areas were now being monitored annually by night-time counts. Before the conservation effort began, they were declining by about 3% per year but, with the programme in place, numbers increased rapidly at a rate of 5% to 6% per year from less than 500 to over 1200 by the mid-2000s.
Cutting corncrake early cover areas on RSPB Coll Nature Reserve © James Duncan (rspb-images.com)
The future of the corncrake in Scotland
In 2015, support from the Scottish Government to farmers and crofters for the conservation management of corncrakes switched from the Rural Priorities Scheme to the Agri-Environment and Climate Scheme.
Changes to the scheme’s prescriptions and payment rates appear to have resulted in a reduction in the area of land with delayed mowing and the degree to which mowing was delayed. Since this switch was made, the annual counts of singing corncrakes have shown a worrying downward trend.
RSPB is investigating this in detail and discussing possible remedies with the Scottish Government and other partners through the Corncrake Calling project. This ambitious project, which was launched in August 2020 thanks to funding from the National Lottery Heritage Fund will work closely with farmers, local community and government to provide these iconic birds with the best possible chance of future.
Counts of singing male corncrakes in Britain 1978-2019
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