Do Corncrakes Crex crex benefit from unmown refuge strips?

Abstract

SummaryCorncrakes Crex crex mainly breed in grassland, where they are threatened by mowing. Conservation requires delayed mowing or modified mowing methods. In large fields, it has been suggested that leaving strips of uncut grass may reduce mortality, especially of unfledged chicks. We attended mowing operations (2012–2015) in the Lower Oder Valley National Park in north-eastern Germany, where 10-m refuge strips were introduced. We documented the escape behaviour of adults and chicks and their use of refuge strips by observations and radio-telemetry. Flightless chicks crossed significantly shorter distances of mown area (< 20 m) than adults. When mowing from the outside inwards, chicks were not able to successfully escape to the field edge at > 31 m, adults at > 60 m distance to the edge and returned to the unmown block. Twenty-three percent of adults, 30% of families and 49% of independent chicks survived in 10 m-wide strips until such strips were either mown or left as refuges. Whereas adults departed the strips the next day, independent chicks stayed for up to 22 days after mowing in 15–30 m wide refuges. We recommend refuge strips for breeding sites where more effective measures cannot be applied. Farmers face less additional effort and lower financial losses compared with delayed mowing. A width of 10 m should be considered as the absolute minimum, because most birds left the cover already > 10 m for the first time and only wider refuges served as temporary habitat for young.