Habitat loss due to drainage and agricultural intensification, and increased mortality caused by modern mowing practices are key threats.
Threats to corncrakes
Threats have made the corncrake officially classed as Near Threatened by IUCN.
Corncrake populations are affected by factors acting in combination. Shortage of suitable tall vegetation as foraging, nesting and brood-rearing cover can occur in spring, before the grass in hay meadows grew tall enough, and again in late summer after hay and silage were mowed.
In some areas there is also a shortage of tall grass habitat in summer because of a decline in hay and silage making. However, even if tall vegetation was plentiful, mowing of a significant proportion of it during the long breeding season of the corncrake can lead to heavy losses of eggs and chicks. Hence a combination of sufficient suitable cover, present throughout the breeding season, and mowing management that gives corncrakes long enough to rear enough young is necessary for the population to persist.
As well as being affected by the timing of hay and silage mowing, corncrake breeding success is also influenced by the method of mowing. Mowing grass in small patches or by methods (Corncrake Friendly Mowing) that allow chicks to run through tall grass to cover that remains uncut can considerably improve chick survival and breeding success.
Predation by birds of prey, cats, mink and otters is the main cause of adult mortality in the breeding areas and some birds are also killed by road traffic and collisions with fences and overhead wires.
Corncrakes migrate to Africa via western France and probably Algeria in the autumn. Substantial kills by hunters and trappers in these areas have not been reported. Further east in Egypt, up to about 14,000 birds are killed per year by trappers, but this is only a small proportion of the large Russian and eastern European population that passes through that area. No clear threats to the corncrake have been identified on its wintering grounds in sub-Saharan Africa.