Nature’s Top 40: Britain’s Best Wildlife. Chris Packham

there is less light in which the waders are able to spot their prey, this is compensated for by the fact that the invertebrates tend to be more active meaning that moonlit nights can often represent very rich pickings even for the plovers that hunt mostly by sight.

      As the turning tide begins to flood in and cover the mud, the different species will be forced to crowd together as the mudflat steadily diminishes in size. The birds usually seem reluctant to leave these feeding areas for the high-tide roost, resulting in them often overlapping one another in a rippling Mexican wave effect up the estuary as progressively more mud becomes covered by the advancing tide. It is only when the last of the mud finally becomes covered that they are grudgingly forced to take to the air in a mass of whirring wings and amid much noise. When the birds rise as one it can be a spectacular sight, particularly if there are large numbers of knot present, like at Snettisham in Norfolk, as they pack very tightly together to form a huge, swirling smoke cloud for the, often short, hop across to their high-tide roost on the nearby gravel pits.

      Waders choose their high-tide roost sites very carefully and tend to prefer sites that have a good all-round visibility, freedom from disturbance and shelter from the wind. The choice of roost usually ends up being a compromise, of course, as the most sheltered sites will invariably have poor visibility, but the favoured locations are usually tried and tested spots such as nearby fields, salt marsh or a remote section of beach above the tideline. Once the roosting birds finally settle, they adopt a posture to minimise heat loss, such as facing into the wind in order to avoid their feathers being ruffled, shortening their neck, tucking their bill under the feathers and standing on one leg. While the birds will undoubtedly sleep for short periods in the roost, they will often keep one eye open and alert for any potential danger. Should a peregrine approach the high-tide roost, for example, the waders will immediately assume an alert posture, with their necks extended and their wings held slightly away from their bodies so they can be ready to take to the air in evasive action. When the waders are forced to roost at night this can present a different problem, as they suddenly become more vulnerable to stealthy ground attacks; in this scenario they will often prefer to roost in shallow water to deter any terrestrial predators, such as foxes, allowing them see the sun rise over the mudflats another day.

33 Machair in summer

       The word ‘machair’ comes from Gaelic and means an extensive low-lying and fertile plain. The term for this habitat encompasses everything from their white sandy beaches, to the calcium-rich dune pasture, to where the sand encroaches on to the peatlands further inland. Taking a walk along the machair in spring when the birds are calling, or in summer when there is the most incredible blaze of wild flowers is like taking a step back to the halcyon pre-industrialised days of farming on mainland Britain.

       Machair

       WHEN

       Late May to August

       WHERE

       West coast of the Outer Hebrides, Tiree, Coll and other small Scottish beaches with a westerly aspect

       The floral extravaganza that is the machair.

      Bob Gibbons

      With its precise requirements for formation and its localised nature, machair is one of the rarest habitats in Europe. In the British Isles, it is found only in the north and west of Scotland and western Ireland, of which almost half occurs along virtually the entire western fringe of the Outer Hebrides. The machair habitat as we know it today was formed at the end of the last Ice age after the melt water from the glaciers deposited enormous quantities of sand and gravel into the sea over what is now the Continental shelf. As the sea level rose, this glacial sediment, which became mixed with the crushed shells from marine molluscs, was then driven ashore by waves from the strong prevailing southwesterly winds to form the characteristic white beaches. Over time a constant supply of this sand caused some to be blown above the high-tide mark and began the formation of dunes. Centuries of constant wind has occasionally broken down these dunes, depositing this fine white sand on to the fields and pastures beyond, even blowing far enough inland to coat some of the peat bogs.

      As machair sand is composed of 80 to 90 per cent crushed shells, these western beaches are white in colour, as opposed to the more typically yellow-coloured beaches on the eastern coasts of outer Hebridean islands, such as North Uist, where the sand is mostly from mineral-based material. Down below the sea line on beaches with a westerly aspect, the sand is repeatedly exposed to the action of the waves and wind meaning it is a highly mobile environment and devoid of any colonising plants, but just above the high-tide line the first few hardy, pioneering plants like sea rocket and sea sandwort begin to take hold. The very presence of these plants initiates the eventual formation of dunes: they provide a barrier to sand particles which then become deposited, and in turn create a bigger obstacle as more sand becomes accumulated by the plants as it is blown up the beach. The number one dune builder has to be marram grass, as its spiky inwardly rolled leaves, rapid growth rate, tussocky nature and deep root system mean that it can thrive in this harsh, sandblasted environment.

      Behind these dunes – which can reach up to ten metres in height – the impact of the wind and salt spray are much reduced, meaning that a larger variety of plants are able to grow in the bare sand. As these plants decay over the seasons, the embryonic soil holds moisture a little more easily and the alkalinity is slightly lowered, meaning that plants such as butter-cups and lady’s bedstraw may be able to take hold, eventually forming meadows as the sand becomes habitable.

      From the end of autumn until at least the middle of May, the machair has been described as a ‘desolate waste of sand’, but equally large areas of the machair can be flooded. This serves to protect these vulnerable grasslands from wind erosion and to provide rich feeding grounds for wintering wildfowl such as barnacle and Greenland white-fronted geese. Atlantic winter storms wash up a huge amount of kelp from just offshore and this forms an additional sea wall along the dune edge, which helps to protect the machair from being inundated by sea water. This kelp, or ‘tangle’, has been collected by the local population ever since Neolithic times as a natural fertiliser and 40 tonnes per hectare is still placed over the machair once it has drained each spring to improve the organic content. The fields are then ploughed to help bind the soil together and to improve its moisture-holding capacity, which in turn makes the grassland more resistant to wind erosion and ready for planting crops.

       The corncrake, a.k.a. Crex crex. So repetitive they named it twice!

      Derek Middleton

      Spring generally arrives late on the machair because of cold easterly winds, but the application of the tangle, the ploughing, and careful grazing before the main growing season help create the perfect conditions for a vast array of wild flowers to grow alongside the planted oats, rye or barley crops. Strict field rotation is practised and, in some of the fallow areas, the floral diversity is so rich that it can reach an astonishing 45 species per square metre.

      Early in the season the white confetti of daisies cover huge areas of machair; come June, the machair turns yellow as buttercups and bird’s-foot trefoil dominate in the drier areas, and silverweed, yellow rattle and marsh marigold thrive on the slightly wetter ground. Later in the summer the predominant colour tends to move to the red and purple end of the spectrum with red clover, ragged robin, self-heal and field scabious taking centre stage. The machair is also famous for its orchids, with pyramidal and fragrant orchids occurring in profusion alongside the unique Scottish marsh orchid at a number of sites on North Uist. The application of very low concentrations of herbicides means that, growing among the crops to be harvested, agricultural weeds, such as corn marigold and charlock that are all but extinct on the mainland, can be found.

      This