OF all the country sounds, to me none is more full of old-world charm than the noisy cawing of rooks. It makes one think of tranquil villages, tucked in sleepy hollows: wisps of curling smoke and the ring of the blacksmith's anvil, and always a rookery in the vicarage elms.
Rooks are the subject of much controversy, which is hardly surprising considering their diverse activities. In the spring they render great service to the farmer, ridding the ground of noxious larvæ and grubs. That destructive pest the leather-jacket (the larva of the daddy-long-legs) is consumed in great quantities. In some way of their own, the birds locate, not only those ploughed to the surface, but also those concealed in the ground.
The rooks' reputation for destruction arises chiefly from their addiction to sown grain and peas, which they dig up and devour with as much zest as they consume the grubs at an earlier season. They are also reviled for their habit of uprooting plants, apparently in sheer destruction. The plant is not their objective, but the grub harboured in its roots, which, had it survived, would have caused many more plant casualties. Thus an apparently wanton action is really a long-term benefit. On balance, the rook is undoubtedly beneficial to man's interests.
Throughout the year rooks are seldom seen except in company. These members of the crow family are often called crows, though this term is used more correctly to denote the carrion crow. That sleek black bird has reprehensible habits, such as egg stealing, which is often wrongly attributed to the rook. In winter rooks congregate in vast colonies, spending the day on their feeding-grounds and returning at night to roosting quarters in a seemingly endless procession.
The rook is a wise and wily bird. When feeding, the flock appears as a casual gathering, each bird intent on his own affairs. In reality they are an organised community, with sentries posted to warn should danger threaten, and rising in unison when the sentry sounds the alarm. They are wise weather prophets too, according to ancient lore. It is said to mean rain when the flock suddenly rises to a great height with much excited cawing and with wild evolutions, then descends rapidly with half-closed wings till near the ground, where they behave normally until obsessed by another spasm.
The height at which their nests are built is governed by their weather predictions. With a fair season in prospect, the nests are established in the topmost branches. Should a season of gales seem probable, they build at a lower level, which results in fewer casualties. I have often noticed this variation in altitude, and have found it a tolerably accurate indication of the weather for the next two months, which covers the nesting phase. I have never compiled statistics, but in general their instinct appears to be sound.
Sooner or later in February, they abandon their winter habits and show increasing interest in the old rookery. During the greater part of the year peace and harmony prevail in the community, but now there arises a period of competition, when squabbles and jealousies are rife. Surviving nests are inspected and eagerly claimed by the enterprising first-comers, while others lose no time in taking possession of eligible sites, guarding their property long before the first stick is laid.
The nesting phase is a period of the utmost importance, comprising far more operations and considerations than are apparent at first glance. Unless the whole performance is efficiently conducted, the species will fail to survive. We see the nests in haphazard array, each apparently just a collection of interwoven twigs in a forked branch, of which there are thousands. There is a great deal more in it than that, however, for the choice of a site is no casual affair, but the result of deliberate survey and assessment. The first sites to be claimed are the selfsame forks in which last year's nests were built, these having been blown down in the winter, and not a single stick being left as a clue. Why should these particular forks be chosen, rather than hundreds of others apparently as good? Simply because they fulfil certain essential conditions, as we shall see.
Elms are much in favour, as they provide the right kind of forks for the bulky nests. A single fork is inadequate, for there the nest would lack adequate anchorage and would rock and swivel to destruction. A multiple fork is essential, for this provides a crutch ensuring stability, and the nest can be built round the branches, not merely within the recess. This fork must also be at the right level, neither too high nor too low, according to the weather prediction. This is the ideal, of course; but it cannot always be attained. We now begin to see that suitable sites are decidedly limited.
The fork is not easily found; for the branches comprising it must all be on one bough. In a gale all then sways as one coherent unitnest, branches and boughwith little movement which might cause damage (Fig. I8). Interlocking branches of adjacent boughs often provide multiple forks, but such a choice would be disastrous. Lashed by a gale, the branches writhing in opposing directions would soon tear the nest asunder. Inexperienced young birds sometimes lack this discrimination. Such carelessness must not be perpetuated, so the welfare of the species is best served by a drastic course of destruction. The laws of Nature are stern in their decree.
Although a number of old sticks may figure in the coarse foundations, the bulk of the nest is constructed of live twigs, nipped off the tree tops by powerful bills. A structure of dead sticks alone, brittle as sticks of candy, would very soon disintegrate. Despite the diligence of the builders some nests make little progress, for thieves and rogues abound, brazenly pilfering in the absence of the owners. When caught red-handed by the irate occupants, lively, battles ensue, usually ending in a rout. When thieves are persistent, one of the owners is obliged to remain on guard.
The cup of the nest is finished with finer twigs, then a lining of dead leaves, mud or dry grasses is added. The cup is unusually deep, like the shape of an egg-cupa provision to prevent the eggs from being catapulted out. As a further safeguard, the eggs are particularly small for the size of the bird. As nest-building progresses, the rivalry subsides and good fellowship prevails once more, each pair being fully occupied with its own particular interests.
By the third week in March some eggs will be in evidence, even if the weather has been cold. There are from three to five eggs in a clutch, blotched with dark brown and olive on a ground of pale green in varying shades (Fig. I9) Owing to the depth of the nests, the eggs are not easy to photograph. At a distance of five or six feet, the viewpoint must be at a corresponding height above the nest level in order to get a sight of the eggs (Fig. I7). In a rookery of two hundred nests, only four or five are sometimes thus accessible. Chestnut trees provide the best sites for camera work, for the branches in the topmost reaches are strong and not too thin, besides being very numerous.
After some three weeks' incubation, in which the males take their turn, the chicks begin to emerge. The young of many species are hatched well covered with down, but those of the rook are born absolutely naked. To compensate for lack of covering their skins are somewhat thick and tough, and dark grey, almost black, in colour. By no stretch of imagination can they be called handsome, or even comely, but as their feathers appear they become more prepossessing.
In one accessible nest I found two chicks in mid-April, the only survivors of a clutch of four eggs (Fig. 20). In spite of sound construction in admirable forks, many nests had suffered depletion in the recent spring storm, and the ground was sprinkled with broken eggs. Should two eggs be taken from a clutch of four, the birds would almost inevitably desert. Not so, however, when depletion arises from natural causes, for I have seen many cases of single eggs being incubated. Complete disasters can be blessings in disguise, for the second broods usually survive the shoot on May 10th.
These ten-day-old chicks had not yet opened their eyes, but blue-black plumage had appeared in patches on head and body while, as in all young birds, the wing feathers showed the most advanced development. When hatched the chicks lie in disorderly array, a jumble of heads and tails; but at quite an early age they assume an orderly arrangement, all heads facing in the direction of the parents' approach, which is always consistent. This compact method ensures mutual warmth and economical use of accommodation, so essential in the case of a full brood, besides providing a smooth surface for the brooding parent. When disarranged the chicks promptly re-establish themselves in their original position, by a process of heaving and shuffling.
Temperature is an important factor in the welfare of birds, which, with their thick covering of non-conducting plumage, are insulated from external extremes. The nesting phase being early in a rookery, the chicks appear before the foliage is out. There they lie, while the parents are foraging, gaping in distress as the relentless sun beats on their backs (Fig. 22). Some birds will shade their young with outspread wings; probably the rooks do the same.
On May 7th activity was at its zenith, with parents working overtime in an effort to appease insatiable appetites. From all directions came a constant procession, with beakfuls of succulent grubs and worms, invariably turning to alight against the wind. And all the time there was a raucous chorus of guttural cawing, reinforced by an undertone of feeble baby squawks expressed in the language of the tribe.
Many of the youngsters had already left home and were perching on branches in the tree tops. There they spent the next few days while their wings developed the strength to fly. Having watched them grow up, it is sad to reflect that the next few days spell doom for the great majority. There they are shot, unable to escape, the few survivors being those still in the nests. Those in the chestnuts have a better chance of survival, since they are hidden in a canopy of dense foliage. To a bird lover it is a tragic procedure; but in other spheres it is deemed necessary in order to keep their numbers within bounds. More than once, let me whisper, I have moved them out of danger and have found them safe and sound after the shoot.
Surveying the scene from the ground, I noticed a youngster sitting by a nest, in what appeared to be an ideal spot for the camera, so I promptly ascended. Reaching the spot, I found him sitting placidly by the side of a nest in the extreme top of the tree. This month-old youngster, a credit to his parents, watched my movements with interest for awhile, then prompted by some inner urge, he suddenly realised that it was past his teatime. To draw attention to this gross neglect, he voiced his sentiments by cawing three times at one-second intervals, every half-minute or so.
Fig 23. He voiced his sentiments in plaintive tones
His tone was plaintive at first, then a decided note of petulance crept in. I wanted a record of the incident, so with camera sighted I waited, determined to snap at the second "caw," regarding the first as a prompting. SNAPbut the caw never came, the only exception among dozens of threes! Such are the trials of a naturalist! I managed to get him next time (Fig. 23), and then left him on his airy perch. By working quietly I had kept him reassured, content to sit still, though an easy line of retreat was available.
Fig 21. Two young rooks which fell from the tree tops
Whilst I was busy aloft, my small son Kenneth was roaming about in the wood. This budding young naturalist, aged seven, was bursting with pride over a capture he had made of two young rooks, about a month oldtwo of several which, through some misadventure, had landed at this lower level. A final snap with my very last film (Fig. 21), a wistful good-bye from Kenneth, then another climb with the wanderers.
We packed the camera and set off for home. At the edge of the wood we paused, thinking we heard a familiar sound. Above the general clamour, in accents decidedly strident, came "Caw!C-A-A-W! C-A-A-A-W!"