A characteristic of the forests of Doñana are the enormous sand-hills—mountains of blown sand dazzling in the reflected sunlight, and devoid of green thing or trace of life, beyond the track of prowling Lynx or Mongoose, or the curious "broad-gauge" vestigia of the tortoise. Stay: there is a thin black strip of moving objects—they are all ants, and that is one of their great highways—a beaten track connecting two great industrial centres. Except on the chosen line—a mere strip barely an inch wide, though hundreds of yards in length—not another insect will be visible on the wastes of sand. To the selected route each member of their infinite community confines his course as systematically as the steamships of our great ocean lines. One cannot resist the temptation of interrupting this well-regulated microcosm. Instantly confusion spreads in the black ranks: around the point of obstruction the intercepted battalions spread out like a fan: the tumult and disorder extend backwards along either column till for yards the sand is carpeted with the fragments of a disorganized host. But these scattered units are each seeking to re-establish their lost continuity. The re-formed column deflects a little to pass on one side or the other (not both), and in a few minutes the "trade-route" has resumed its former monotonous regularity.
Elsewhere the sand-wastes are clothed, especially in their deeper dells and hollows, with cistus-scrub or tamarisk, and the stone-pine (Pinus pinea) somehow finds sustenance and even luxuriates. How plant-life can survive on the remnants of pulverized rock is a mystery—though here, perhaps, the deep-seated roots strike into alluvial soil below—and no more comprehensible in view of the analogous fact that the vines producing the richest Spanish wines also flourish in equally ungenial soils. The vintages of Jerez are garnered from grapes grown on arid and silicious soil: the strong red wine of Val-de-Peñas, so grateful in torrid Spain, comes, literally, from a "valley of stones," and in the Alto Douro the vineyards occupy hillsides composed of little bits of (what looks like) broken slate and disintegrated shale, so little coherent, that the slopes must be terraced before they are cultivable. Strange anomalies—plant a vine in rich soil, and you get vine leaves—in tropical lands, the vine becomes a barren evergreen—in arid soil or shale, it produces nectar.
Firm and compacted as appears the substance of these sand-hills—the sandstone of a future age—it yet retains, to some extent, its shifty and unstable character. At intervals its masses elect to move onwards and to engulf forests over which, for centuries, they have impended. Immediately below where we sit, the ridge terminates, abrupt as a precipice. Two hundred yards beyond, the sloping sand-foot is studded with half-buried pines—several forest monarchs already entombed to their centres, alive, but struggling in their death-throes. Of others, farther back, only the topmost branches protrude, sere, yellow, and dead, from the devouring particles. And beneath those glistening sands, hidden far from sight, doubtless there rest the skeletons of buried forests of bygone days.
Just above us in the peak of the stone-pine under whose shade we enjoy the midday rest, is a huge platform of sticks—a deserted throne of the king of birds. Now this eyrie is deserted, the daylight shows through its centre, and the tree is occupied by different tenants—a pair of Cushats: before now we have seen them share the same tree with the tyrant. Bird-notes are hushed during the midday heat, and silence reigns over the forest: presently from afar comes the strident kark, kark of the Raven, and then from mid-air resounds the musical scream of a Kite floating in the heaven above.
Riding along the open glades, the most conspicuous birds in spring are the brilliant Rollers and Hoopoes, parties of Hawfinches and Crossbills, always shy, an occasional Spotted Cuckoo (C. glandarius) or Southern Grey Shrike (L. meridionalis); handsome Woodchats (L. rufus) scold in every bush, and various Finches and Woodpeckers, Tits and Creepers, enliven the woodlands, and sprightly Rufous Warblers the drier plain. Among the cane-brakes and carices that fringe the marshy hollows skulk several other warblers—the Great Sedge and Black-headed Warblers (S. arundinacea and melanocephala), Orphean, Cetti's, and the little Fantail, besides our familiar Willow-Wrens, Chiffchaffs, Blackcaps, Redstarts and Robins—the latter resident, and very bright in colour. The Black Redstart has already disappeared (April), but from day to day one sees our British migrants arriving, resting, or passing forward on their northern journey. Swallows especially are conspicuous: to-day the air is alive with them, sweeping along the open glades: to-night they roost in chattering hosts in the trees around our camp—to-morrow they are gone, not a swallow remains: and this occurs a dozen times during April and May.
On April 13th and two following days there occurred a conspicuous "through transit" of Pied Flycatchers, and two days later (in another year) the brushwood was alive with Redstarts, all on passage. On the 25th we were visited for a couple of hours by hundreds of Alpine Swifts: and the same evening the large Red-necked Nightjars (C. ruficollis) arrived, to add their churring note to the crepuscular chorus of frogs and night-birds for the rest of the spring and summer. One evening in May, while watching a pair of Golden Orioles to their nest, I witnessed a rather curious eviction. A Spanish Green Woodpecker (Gecinus sharpii), her gullet crammed with ants, flew to a hole in a wild-olive, but was met at the entrance by a furious Little Owl (Athene noctua), which soon drove the clumsier bird (which had no idea of self-defence) screaming to the shelter of some brushwood. Soon after, her mate returned, but met with a similar reception, the savage little owl perching meanwhile on an adjacent branch, where he sat bolt upright, all fluffed out, and snapping with rage. On examining the place, I found the woodpeckers had a numerous family, nearly ready to fly: while the owl had deposited a single egg in an adjoining hole. The execution of the aggressor seemed, at first, the only means of saving this thriving family, but, on second thoughts, I decided that the justice of the case would be met by removing the defendant's egg, and filling up his hole with sticks.
The Orioles' nest I shortly afterwards discovered, built in a white-elm, at the extreme end of a long pendant branch, the whole of which it was necessary to cut down. This nest, however, was empty. The Golden Orioles do not lay till nearly the middle of May, and from the shyness of the old birds, and the aërial situation of the nest, their eggs are among the most difficult to obtain.
During the early part of May we found many nests of Hoopoes, some in hollow trees, one in a ruined outhouse, which we were using as a stable, and which, in a previous year, had been similarly occupied by a Roller, and always affords a home to two or three pairs of the Spotless or Sardinian Starling (Sturnus unicolor), a species which, in spring, replaces the common kind. On the outskirts of the woods were many nests of Goldfinch and Serinfinch, Common and Green Linnets, Blue and Great Tit, Willow-Wren, Woodchat, &c.; and in the open rushy glades, those of Black-headed Warbler, Blackcap and Garden Warbler, Whitethroat, Spotted Flycatcher, Grey-headed Wagtail (Motacilla cinereocapilla), and others. I looked in vain in these pine-woods for the Crested Tit, which occurs near Gibraltar, and which my brother found numerous in Navarre. On the 10th May I found a couple of Nightingales' nests in the tiny garden-patch adjoining a forester's cot, and a week later obtained several nests of the Melodious Willow-Warbler (Hypolais polyglotta) with their beautiful vinous-pink eggs; later still (May 28th), those of the Rufous Warbler (Ædon galactodes) among the cactus-bushes:—but this is getting suspiciously like a catalogue.