This article was originally published in the Journal of the Wildlife Sound Recording Society Vol4 No3 Spring 1982
Rooks Corvus frugilegus clan together for feeding, roosting and especially for nesting. Most breeding rookeries are situated close to villages or farms, being distributed largely over agricultural Britain. High, treeless or moorland country is not suitable for rooks and nesting is uncommon in large, dense woods. Further, as rooks are big, conspicuous birds with raucous voices, there is no difficulty for the recordist in locating them or, in most instances, having access to their breeding areas.
Rook on a fence-post at Stonehenge, photo Richard Mudhar
Nevertheless, it is on the account of the proximity of rookeries to agricultural districts that recording problems occur; farms are now highly mechanized and motor traffic moves through the village lanes surprisingly early in the day. The country electricity supply also brings difficulties for the recordist, with transformer hums or the rattle of milking parlor apparatus. Furthermore, a few isolated farms still run their own electrical generators. Contrary to the views of many recordists, there are hazards even in attempting to record rooks, although, admittedly they are of a different nature than those experienced when taping meadow pipits Anthus pratensis on exposed heaths, for example, or guillemots Uris aalge on sea-cliff ledges.
A Somerset dialect name for the rook used to be 'church parson', obviously referring to its sombre plumage. An old group term for rooks was a 'congregation' so clearly the birds had ecclesiastical associations in some places. Another country name was 'croaker', perhaps suggesting some inharmonious responses of the congregation at matins or evensong but, anyway, the name does emphasis the noisy character of the bird.
Yet rook sounds are by no means all harsh. Should one be near a rook as it flies over, the flight-sounds caused by the wing-excursions are surprisingly musical and the approaching bird might even be thought, on occasions, to be a Mute swan Cygnus olor, before it has been sighted. Often, the pitch of the flight-sound changes noticeably as the rook passes, presumably illustrating Doppler's physical principle. There seems to be individual variation in the production of these high-frequency wing sounds: sometimes rooks have flown very near me, yet almost in silence. Maybe the effective speed of the bird, or strength of its wing-beat at the time, are factors in this.
Rooks' vocalizations appear to be varied and are not, in any case, just variations on the cawing theme. At times, rookery noise is decidedly mammal-like or it may have sound elements like those heard at a heronry. Even so, caws do account for the majority of the utterances and these are quite distinct from the deeps croaks of the carrion crow Corvus corone, with which the rook is confused by some people, including a few who live in the country. The main differences, apart from the rooks' habits of gregariousness, are the bare, white bases to the smaller bills of adult rooks and the rounded ends of the tails, as seen in flight. The tail-ends of carrion crows are straight, when viewed from below, and there are no naked patches at the base of the powerful beaks. Fairly obviously, cawing is most likely to be heard at rookeries during breeding, but the autumn roosting sites must not be overlooked. Many roosts are used later as breeding rookeries, but not necessarily so. Nearly all roosting sites, however, have been nesting areas at some time. Tall trees are normally required, nowadays mainly oaks, beech or Scots pines. Following the loss of elms, other trees have been colonised, notably willows.
Rook Caws at Caerlaverock, January 2009
Cawing is a feature when rooks congregate at roost, often following a flight involving gymnastic swoopings, twistings and tumblings. Caws of all varieties are heard at the breeding rookery, as already noted, especially as the birds lay claim to the nest-site and when building, usually during February and March. At this time, display between the sexes is frequent, with bowing and wing-flapping occurring, either on the tree or on the ground on pastures between bouts of feeding activity. The murmuring cawing background of rooks as they assemble in their trees is, to my mind, a comfortable and reassuring sound. Rooks and their calls appealed to Gilbert White, himself a country curate, when in The Natural History of Selborne, he wrote of them: "...and making a loud cawing, which...becomes a confused noise or chiding; or rather a pleasing murmur, very engaging to the imagination.."
Caws of a different intensity and quality are heard in the rookery in connection with sexual display, courtship feeding, nest building and stick pilfering. Alarm caws are short, loud and commanding; rooks are rarely surprised and in any rook assembly an individual always seems to be on look-out duty. If a potential predator should approach a rookery, and sparrowhawks Acciptier nisus or buzzards Buteo buteo would be regarded as enemies, the alerted rooks fly out to mob the intruder, circling and calling in a combined roar of commotion. Cawing increases as darkness starts to fall and roosting commences, but rookeries are rarely silent. There are occasions, however, when noise does cease. Following a phase of increased clamour, the rooks will suddenly fly from their trees in silence, as if at a signal, although this behaviours does not often happen. It appears to resemble a 'dread' flight, as often occurs at terneries.
At the rookery, twigs and branches get depressed and are moved to give mechanical sound, even on the stillest of nights. Rooks are restless before they roost, even changing their positions in the trees and cawing successively, before they seem satisfied. In the middle of the night, cawing often occurs, occasioned perhaps by a bird jostling its neighbour, or could it be that some rooks are poor sleepers? Sounds are also uttered when rooks rock on their roosting branches during spring gales; they can be observed at night if the moonlight is bright enough. Under such circumstances, rooks have remarkable ability in clinging to their high, swinging perches.
That the amplitude and pitch of cawing can vary between individuals can be verified as two birds fly overhead on their way to field or rookery or to search for nest sticks. The difference in the quality of cawing utterances of similar duration given by two individuals under the same circumstances can be surprising; of course there is no means of knowing the sex of the calling birds. When rooks become excited, because of annoyance with neighbours or for sexual reasons, then caws may become prolonged and high-pitched, rising stridently, sometimes to nearly a shriek.
There are other high-tones calls beside the modified caws. One of these is a mewing utterance, which is reminiscent on the note of a buzzard; it appears to be made as a contact call, but probably under conditions of stress. Many ornithologists liken this call to one given by the herring gull Larus canus, or it may suggest the yapping of a small dog. The call is made equally whether the bird is perched or in flight; I suspect that it is made more frequently during the breeding season than at other times of the year. Mainly heard during April and early May are the high-pitched wailing calls and gurgles of the nestlings begging for food; I find the sounds nostalgic and obviously they suggest successful breeding to that time at least.
Another call, commonly heard while nesting is in progress, is a short low-pitched croak or rasp. Some observers have mentioned this as being similar to the croak of of a raven Corvus corax, but it has nothing like its carrying power or intensity. The sound suggests a possible mechanical origin, although I am sure it is really a vocalization; I feel that it has similarity with a brief woodpecker-type drumming or, at times, one is reminded of the alarm rattle of a mistle thrush Turdus viscivorus. The call is frequently made during flight but is also heard from the tree-tops. No doubt it serves as a contact all, perhaps releasing a build-up of nervous energy.
Rooks also make a call rather like that of a jackdaw Corvus monedula, but caution is needed here because of the habits of jackdaws. These birds often associate with rooks, as do starlings, Sturnus vulgaris, when they are feeding on pasture or arable land. In addition, vocal flocks of jackdaws are often seen to visit rookeries, landing on trees adjacent to the nests or, occasionally, close to the incubating birds. Curiously the visiting and often noisy jackdaws do not commonly incite any antagonistic reaction from the rooks. Apart from the interest of the vocalizations to the recordist, the naturalist cannot fail to be intrigued by the activities of rooks. To watch the birds carrying in twigs to the rookery heralds the nesting season and, in due course, mud and earth is carried to bind the sticks together; further rooks pull off sprays of foliage, often conifer or evergreen, either to add to the nest or just to carry and drop to the ground or fight over and tug with another rook.
Later, the begging young are fed a good, meaty diet of wireworms or leatherjackets, conveyed in a parent's bulging throat pouch. of course, rooks do eat grain and, just occasionally, they will take fledglings or eggs. The real bird thieves of young birds and eggs, however, are magpies Pica pica, jays Garrulus glandarius and carrion crows. On balance, no matter how common, rooks probably have little or no adverse effect on farming yield or wildlife in general. Rooks can surely live in equilibrium with agriculture; the conversational rook with its dark but reflective plumage of greens and blues enriches any rural scene. To the wildlife sound recordist of the rook, with its especially varied sound vocabulary, present a subject full of questions and interest. The sounds of rooks are still understood only very incompletely; a study of rook vocalisations could have practical implications, considering the normal close association of the bird with agriculture and its community.
Rookery, Eskmeals, Cumbria 5 April 1980 recorded by Roger Boughton