ONE OF Scotland's rarest breeding birds, the corncrake, has suffered a poor season this year, with numbers dropping by nearly a fifth.

In RSPB Scotland's annual survey, the number of calling males recorded fell by 17% to 1069, down from last year's 45-year high of 1289.

The elusive pigeon-sized birds breed in Scotland, in only a few isolated parts of the country, mainly on the islands, over the spring and summer, then migrate to Africa in winter. The Isle of Tiree holds the most corncrakes, with 333 calling males counted in 2015.

Nearly all parts of the country that corncrakes occupy witnessed a drop in numbers this year, except for a few places like the islands of Islay and Iona, which both had a slight increase, and the Isle of Mull which stayed the same.

Corncrakes also suffered a decline in Scotland back in 2013 - with a 23% compared with the previous year - but they did recover in 2014. It is thought that the exceptionally cold, late springs in 2013 and 2015 are the reason behind the reduction in the number of males calling.

Despite these recent fluctuations, however, corncrakes have recovered hugely since the early 1990s. At that time the species - which, in the 19th century, was common right across Scotland, England, Wales and Ireland - had dwindled to just 400 calling males. These were almost entirely restricted to a few Scottish islands.

Research by RSPB Scotland identified changing agricultural activities, especially a shift to earlier mowing of hay meadows and silage fields, as the main cause of the declines.

In 1991, a conservation programme started, together with the Scottish Government and Scottish Natural Heritage, to design corncrake management options and, critically, with farmers and crofters to actually deliver the habitats these birds need. This programme has become an internationally famous example of cooperative conservation for farmland wildlife.

RSPB Scotland head of habitat and species, Paul Walton, said: "The corncrake has recovered well since the early 1990s, and that's thanks to agricultural communities on the islands. But now that recovery has slowed and numbers are fluctuating, we think in response to cold spring weather.

"This species remains a huge conservation priority in Scotland," he said. "We must remember that the corncrake remains highly localised - though numbers have increased, the conservation programme has not yet succeeded in spreading the population further than its low point in 1991. It is difficult to fund crofters to deliver land management in areas where corncrakes are currently absent - but that's the only way to start increasing the birds' range - the vital next step towards a robust and secure national population."