Flanking the marisma and separating it from the dry lands of Doñana, there rises rampart-like a swelling range of dunes--the biggest thing in the sand line we have seen on earth. For miles extend these mountains of sand, unbroken by vestige of vegetation or any object to relieve one's eyesight, dazzled--aye, blinded--by that brilliantly scintillating surface, set off in vivid contrast by the azure vault above.
Should a stranger, on first seeing those buttressed dunes, be seriously informed that their naked summits constitute a favourite resort of wild-geese, he might reasonably suspect his informant's sanity, or at least wonder whether his own credulity were not being tested. Yet such is the fact--one of the surprises that befall in Spain, the _pays de l'imprévu_.
The paradox is explained by the stated necessity in wild-geese to furnish their gizzards with store of grit or sand for digestive purposes.
This supply, so long as the marisma is dry, they are able to obtain from those raised ridges of calcareous debris (already described, and known locally as _vetas_) which here and there outcrop from the alluvial wastes. But when winter rains and floods have submerged the whole region and thus deprived the fowl of that local resource, they are forced to rely upon the sand-dunes aforesaid and to substitute pure sea-sand for their former specific of calcareous grit or disintegrated shells. To the sand-dunes, therefore, in the cold bright mornings between October and February, the skeins of greylag geese may be seen directing their course in successive files, in order, as the Spanish put it, "to sand themselves" (_arenárse_).
A notable fact (and one favourable to the fowler) is that, though these dunes extend for miles, yet the geese select certain limited areas--or, to be precise, the summits of two particular hills--for alighting, and this despite their being regularly shot thereat, year after year.
With the first sign of dawn the earlier arrivals will be heard approaching; but the bulk of the geese come in about sun-up and onwards till 9 A.M. Geese arriving high (having come presumably from a distance) will sometimes, after a preliminary wheel, suddenly collapse in mid-air, diving and shooting earthwards in a score of curving lines--as teal do, or tumbler-pigeons; but with these heavy fowl the manoeuvre is executed with surprising grace and command of wing. Their numbers vary on different mornings without any apparent cause; but it may be laid down as a general rule that more will come on clear bright mornings than when the dawn is overcast, while rain proves (as in all wildfowling) an upsetting factor. Sometimes, even on favourable mornings, no geese appear. Occasionally, in small numbers, they may visit the sand in afternoon.