Action: Use mowing techniques to reduce chick mortality
- A review from the UK found a large increase in corncrake Crex crex populations in the UK following a scheme to delay mowing and promote corncrake-friendly mowing techniques.
- One replicated controlled study from the UK and a review from the UK found lower levels of mortality of corncrakes and Eurasian skylark Alauda arvensis when wildlife-friendly mowing techniques were used, compared to other techniques.
During mowing and harvesting operations, ground-nesting birds frequently remain in long grass or crops for as long as possible. If mowing/harvest occurs from the outside of the field inwards, this behaviour can leave the birds trapped in the centre of the field and killed as the last patch is harvested. Adjusting mowing techniques, for example starting from the inside of the field, can therefore allow chicks to escape into field margins.
Supporting evidence from individual studies
A replicated controlled study in three areas in Ireland between 1992 and 1995 (Tyler et al. 1998) found that corncrake Crex crex chicks were more likely to survive in hay and silage meadows when they were mown from the inside-out (I-O), compared to the traditional outside-in (O-I) mowing pattern (68% survival for 76 chicks in I-O fields vs. 45% survival for 31 chicks in O-I fields). Most chicks (80%) were killed during the last eight sweeps of the harvester for O-I and the last five for I-O, and mortality was zero for both methods when the nearest tall vegetation was within 5 m of the edge of the field. Chicks that were more than one day old were able to move fast enough away from the mower to escape, so long as a route to unmown cover was available.
A 2000 literature review (Aebischer et al. 2000) found that the UK population of corncrakes Crex crex increased from 480 to 589 males between 1993 and 1998 (an average rise of 3.5%/year) following schemes to get farmers to delay mowing dates and to leave leaving unmown ‘corridors’ to allow chicks to escape to field edges.
A review of four experiments on the effects of agri-environment measures on livestock farms in the UK (Buckingham et al. 2010) found one trial from 2006 to 2008 that tested the effect of mowing techniques to reduce mortality of Eurasian skylarks Alauda arvensis nesting in silage fields. Preliminary results showed that chick survival was strongly affected by the type of machinery used. Survival was four times higher using wider machinery and reducing the number of machinery passes than without these changes. However, the number of new birds produced each year (productivity) was more sensitive to re-nesting rates than chick survival. This study formed part of a Department for Environment, Food and Rural Affairs (Defra) funded project (BD1454) for which no reference is given in the review.
- Tyler G.A, Green R.E. & Casey C. (1998) Survival and behaviour of corncrake Crex crex chicks during the mowing of agricultural grassland. Bird Study, 45, 35-50
- Aebischer N.J., Green R.E. & Evans A.D. (2000) From science to recovery: four case studies of how research has been translated into conservation action in the UK. Pages 140-150 in: J.A. Vickery, P.V. Grice, A.D. Evans & N.J. Aebischer (eds.) The Ecology and Conservation of Lowland Farmland Birds. British Ornithologists' Union, Tring.
- Buckingham D.L, Atkinson P.W., Peel S. & Peach W. (2010) New conservation measures for birds on grassland and livestock farms. Proceedings of the Lowland Farmland Birds III: delivering solutions in an uncertain world, 60.