By Rosewood Farm, Aug 28 2017 03:00PM
The Corncrake (Crex crex) was once a common species in the UK and it’s hard to deny that modern farming methods are responsible for pushing the species to the north western fringes of our islands. They spend only the summer months in Western Europe, breeding here before returning to winter in sub-Saharan Africa. They are one of three globally-threatened species identified by the UK Biodiversity Action Plan.
A secretive bird, the corncrake is more often heard than it is seen, preferring to creep and hide in long vegetation to avoid danger rather than flying away or crossing open ground. This is particularly the case when nesting or with young chicks that are unable to fly. This characteristic behaviour is the major reason why corncrakes have been so vulnerable to modern farming practises. Traditional hay cutting by scythe would start at one side of the field and continue to the opposite side. This, along with the time taken to mow a meadow, allowed the birds to escape through the uncut crop. Unfortunately the introduction of mechanical mowing, first by horses or oxen, and later the tractor, changed the way meadows were cut with continuous initial mowing around the outside creating open ground and cutting off their escape route.
Further changes included the cutting of meadows creeping forward into June or earlier, particularly as the technology developed to make silage, which requires less continuous dry weather, rather than hay. Although, as their name suggest, corncrakes were once associated with cornfields too, feeding on the seeds & insects in weedy crops, the advent of pesticides completely removed this habitat.
In 1992 a reintroduction programme was started by the RSPB on its reserve in Cambridgeshire. Along with conservation efforts in the Western Isles of Scotland, the numbers rose but their range remains limited. Meanwhile, the Yorkshire Ings was the only place in England that managed to hold on to its natural breeding population, despite almost becoming extinct here in the late 1960’s, this has continued to the present day through legal protection of the habitat in the Lower Derwent Valley SPA.
- The photo shows method 1 in the centre with conventional mowing in the two fields to the right of the picture -
Modern day land management presents new threats for the Corncrake which protection alone is unable to address. The loss of cattle farming in Scotland seriously threatens the corncrake recovery and we are now in danger of finally experiencing the same effect here in Yorkshire. Although the birds prefer cover, they favour lighter vegetation that is removed at least annually by either cutting or grazing. Cattle grazing near hay meadows provides areas of longer vegetation for the birds to inhabit between the hay cut and migration. The recent decline of cattle grazing in the valley puts further pressure on the birds.
The good news is that while chick mortality is high, this provides plenty of potential for recovery of numbers by improving survival rates & encouraging fledging of second broods. Our cattle grazing in & surrounding the ings provides some safeguard against habitat loss but as we also manage traditional hay meadows we didn’t want to contribute to their declines. An internet search revealed very little practical advice or experience of ‘corncrake friendly mowing’ (CFM) techniques from anyone who had actually carried it out. All of the available guides contained simplistic diagrams of mowing patterns that didn’t really represent real-world scenarios. It was clear that if farmers like ourselves are to be encouraged to adopt corncrake friendly management then providing practical advice on how to go about it is an absolute necessity, so we decided to document our experiences.
Now, a word of warning to the casual reader who isn’t interested in carrying out CFM themselves- you may want to skip to the end as this is the boring technical bit;
We began mowing in mid-july using a four-wheel drive 72hp tractor and offset 1.64m drum mower. The traditional straight lines are easier to set & maintain by using the field edges as a guide when operating machinery. Starting in the middle and working outwards is a tractor driver’s nightmare but this was the first of three techniques we tried in an almost-square field of 12.77 ac (5.17 ha). We marked out a centre point by pacing across the field in a north-south and east-west direction, returning half the way back, then following the opposite trajectory to find where the two points met.
Cutting started with three passes on either side of the centre point in straight lines to create a central block of approx 10 m by 10 m. The next pass started on the right and continued around in an anti-clockwise direction and proceeded in a spiral until the edges of the field were reached. On three sides of the field this was reached at the same point, but the remaining side required several more passes. In order to avoid long distances of travel while not mowing, we took the decision to mow in either direction on the corners, returning passes in a clockwise direction requiring driving on the uncut crop. The field margins were cut as a traditional headland in an anticlockwise direction to maintain the uncut margins. The crop was spread after mowing then turned and rowed up conventionally for baling.
The second method involved a smaller 5.35 ac (2.16 ha) field of almost square shape with some trees and bushes within. Cutting a traditional headland on two opposing sides created an area for turning while the other two margins were kept intact. A mid point was cut between the two headlands forming a central opening followed by passes on either side in each direction. At first this approach involved some tight turns, and ended with some very long turns on the later passes. Although this makes for efficient method for very long, narrow fields, the square shape reduced the turning:mowing ratio to unsustainable levels.
As per the RSPB guide to CFM a round field containing a central pond or copse is the ideal shape for most efficient mowing but also one of the least likely shapes encountered, so I question its value as an example. Our final field contained a pond close to the margins of the south-eastern corner and was also the most challenging. Beginning by circling the pond in a clockwise direction, followed by subsequent anti-clockwise passes was reminiscent of the first example, however this created a large irregular area on the north & western sides of the field. With a conventional headland created on the western side and the pond margins on which to turn along the eastern side, we proceeded to mow conventionally, subsequently opening up several sections and mowing until a narrow strip was left in each. These were left overnight to give the birds chance to escape to the larger field margins under the cover of darkness.
This represented the most conventional method and followed a technique suggested by farmers on the Cowal peninsula on the west coast of Scotland. Although differing little in terms of time and efficiency compared to conventional mowing, the break in mowing, depending upon the layout of the farm, may not be practical for efficient working. This may be avoided by flushing any birds manually, on foot, before completion of mowing.
It is commonly accepted that delaying mowing until August negates the need for CFM, giving breeding birds the chance to fledge before mowing commences. However this may not be possible later in the season due to time constraints. Staggering cutting dates also allows for a greater variety of vegetation lengths across breeding habitats, as preferred by post-breeding corncrakes and other ground nesting birds, than clear cutting over a shorter period of time. It is also less desirable for farmers to sit-out periods of favourable haymaking weather whilst awaiting an uncertain August.
Given the small numbers of birds present it is not possible to quantify the effectiveness of either method in terms of chick survival but RSPB figures suggest that survival rates increase from 40 to at least 80% with CFM. However, with knowledge of corncrake behaviour it is reasonable to assume that method 1 gives the greatest opportunity for escape. Whilst this represents a reasonable efficiency compromise, it may be less desirable to tractor drivers having to work in the round. The method is also limited to largely square fields containing few obstacles.
Method 2 is largely only practical for narrow fields, in which case it is likely that efficiency would rise significantly to almost 100% and the method does still provide good opportunity for escape.
In terms of efficiency method 3 seems hard to beat but it does still force corncrakes into an ever-decreasing island of grass and creates open ground, therefore increasing the chances of mortality. Flushing birds on foot before mowing also gives an opportunity to survey numbers for a relatively small decrease in efficiency. In this case 0.5 hours spent flushing would represent 87.5% efficiency.
If the breeding success and spread of corncrakes it is to improve it is important that farmers and land managers are encouraged to consider methods to reduce mortality alongside habitat provision. Any losses in efficiency also represent a financial cost to the farmer which must be taken into consideration otherwise this might lead to further abandonment and loss of favourable corncrake habitat.
If you know of any alternative methods or experience of CFM please share & discuss them using the comments below;