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Saturday 20th December, 2014

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Grasslands For Barn Owls

Ideal Barn Owl habitat is usually described as ‘tussocky permanent grassland’, but what exactly do we mean by this? What is ‘permanent’ grassland, and why does it need to be tussocky to attract Barn Owls? Basically, the answer to the latter question is - ‘because this is where the Barn Owl finds its food’.

To sustain itself and a mate, as well as a healthy brood of owlets, a Barn Owl needs a high proportion of Short-tailed Field Voles in its diet. While Barn Owls do take other prey such as Common Shrews and Wood Mice, these are of only secondary importance and it is the Field Vole which is the key to Barn Owl survival and conservation.

The Field Vole makes its concealed runways beneath the ‘thatch’ of fallen dead grass stems and nests in tussocks of grasses such as Cocksfoot, False Oat Grass, Meadow Foxtail and Meadow Fescue. Since the juicy stems of these succulent grasses also comprise the main diet of the Field Vole it is obvious that permanent grassland is essential if this cycle is to prosper. Heavy grazing and intensive cultivation destroy the all-important tussock structure and leafy ‘thatch’ and the Voles die out. With their disappearance go the Barn Owls and the many other forms of wildlife who depend upon this type of habitat. Because of this, the temporary ‘ley’ grasslands of Rye Grass and Clover which are so commonly sown these days are of no use whatsoever to wildlife, for they are at first heavily grazed, then ploughed then returned to arable within a period of 3 to 5 years. Because of this they harbour no Voles whatsoever.

Permanent grasslands usually comprise native grass species which have not been planted by man and have not been cultivated for many years. In days gone by many of these would have been cut for hay on an annual basis but now, with more sophisticated machinery and the advent of silaging, the old hay meadows have become a thing of the past. Only in game-rearing areas are rough grassland corridors and headlands left for wildlife. The heavily grazed pastures of the North are nowadays almost entirely devoid of wildflower meadows, although in Southern counties a few arable and cereal farmers occasionally leave wide borders to their fields in order to help the conservation initiatives currently being undertaken on behalf of Barn Owls, game birds, farmland birds, wildflowers and butterflies. Sadly, such areas have become tiny oases of intensive agriculture and this fragmentation has greatly lessened their conservation value. Only if we can recreate suitable grassland areas and link them together can we hope to save the Barn Owl and other forms of wildlife in the long term.

The problem is how can we go about recreating and managing such a habitat? To maintain the essential litter layer and thus a small mammal population that is vital to a Barn Owl’s survival, an area of rough grassland should be managed on a 3 or 4 year rotation. In the Autumn, a third or a quarter of the grass needs to be cut, ideally no lower than about four inches so that the litter layer is not completely destroyed as this is where the small mammals live. Cutting allows light in for new grass growth and field voles feed on the new juicy grass stems. It may be necessary to keep track of which area(s) have been cut. Post markers may help to mark which area is next in the rotation. To start a rotation is it necessary to cut a third or quarter in the Autumn of the first year. Any cuttings must be removed. Whatever you do, always avoid cutting all the grass in one go.

Many well-respected authorities still argue fiercely about what constitutes the best management policy for ‘permanent grassland’. Some recommend the creation of old-fashioned hay meadows, others suggest light grazing by livestock as the answer. Personal experience has shown us that in neither case does this result in ideal Vole habitat (though the former is best for wild flowers and is better than most other forms of management, especially if wide margins of ‘rough’ can be left at the sides).

A traditional hay field is cut once a year usually at the exact time when Voles and Barn Owls are producing their young! The cutting of the hay destroys the Vole nests and kills that year’s crop of young Voles with obvious dire consequences on the Owls which depend on them. It also removes the opportunity for a ‘thatch’ to develop and for this reason the new concept of wildflower meadow creation is not really the optimum answer for Voles and Owls. However if areas of such meadows can be left uncut in rotation, reservoirs for Voles can be created, while the herb-rich grassland of the cut areas will provide the floristic beauty and insect-rich habitat most managers are aiming for.

Management of wildlife areas by light grazing by livestock is much in vogue at the present time and is a favourite ploy of many wildlife trusts. However, this is quite definitely NOT a good management technique for creating Vole habitat. Even if the grazing regime is so light that the tussock structure survives, a close inspection will usually reveal that there is little evidence of Vole presence. The reason for this is obvious, for apart from the dangers of trampling, the grazing eliminates any chance of a build-up of dead grasses (i.e. ‘thatch’) under which the Voles can live and feed. We have monitored many examples of this form of grassland management and can state categorically that in every case light grazing has resulted in the Voles disappearing.

Although the above seems to suggest that the best regime for the creation of Barn Owl (Vole) habitat is to leave large areas unmanaged, this is not the case. There comes a point when the litter of dead grasses becomes so dense that it excludes light and prevents the emergence of fresh shoots on which the Voles can feed. Scrub, docks, brambles and thistles also develop and therefore some management control is required such as that described for the Owl Centre.

With the exception of a few areas such as South West Scotland and South Lincolnshire (thanks to the Hawk & Owl Trust Scheme) continuous stretches of rough grassland are almost impossible to find in Britain. As a result many Barn Owls attempt to fly alongside roadside verges and suffer huge mortality after collisions with vehicles. The fact that so many are killed in this way proves how scarce optimal habitat is these days. Ideally, a pair of Barn Owls needs some 120 acres (48 ha.) of permanent rough grassland such as described above. However in Lincolnshire they have learned to hunt linearly along 20 feet (6 m.) wide corridors for some 10 miles (16 km.). But, please, if you cannot manage this, even a smaller area helps, especially if we can make this link up with similar areas in a patchwork-quilt fashion. Even if you only have a garden, a ‘wildlife grassland patch’ is a positive step forward - especially if a million of your neighbours follow suit!


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