(30) SOME BREEDING HABITS OF THE ROOK. BY G. K. YEATES. THE following notes on the Rook (Corvus f. fntgilegus) were taken at Stodmarsh, Kent, from an observation post in a rookery during March and April, 1932. Observations were taken on ten occasions between March 14th and April 17th, and on six occasions from the hide itself, sessions lasting on an average from two to two and a half hours. The rookery was a large one, there being some 350 nests, built in the following trees : Scots pine (about 60 per cent.), oak (about 25 per cent.), beech and elm (about 15 per cent.). The hide was so situated that* four nests could be watched well, while eight others could be seen adequately. The following remarks will be taken chiefly from notes made on behaviour at the four nests above referred to. Two were to the east of the hide, which I shall hereafter refer to as nests A and B, and two to the west, hereafter called C and D. At nest C I could be certain which was the female as I had seen the birds mating, and the female had a white chin, which her much larger partner lacked. At the other nests I had no such mark to help, but there was an appreciable difference in the size of the birds, the larger bird being from my observa• tions the male. During observation-sessions in the hide three periods in the breeding life of the Rook were covered : (1) the later courtship habits ; (2) the period during incubation ; (3) the period after the eggs had hatched until the young were half- grown—in one nest, C. (1) The Later Courtship Habits. As will be seen from the date of starting work, courtship was already well advanced, with the result that only its later stages could be watched. Mating apparently takes place well into the incubation-period, for on March 27th it occurred three times during z\ hours at nest A ; once attempted (un• successfully) on nest B ; on March 31st once on nest C, where to my certain knowledge the eggs had been laid at least twelve days, and I suspect longer. At this stage mating takes place by two methods of approach. In the first there is definite courtship. The male (at nest B) alighted above the nest on which the female was sitting, flying down to alight behind his mate, where he cawed twice. Finding that did not draw her attention, he hopped round level with her, where he bent his legs and stretched forward his neck, cawing VOL. xxvi] BREEDING HABITS OF THE ROOK. 31 deeply twice, his beak level with her's and his tail fanned out to each caw. Finding that still futile he hopped savagely on to her back, from which he was viciously repulsed. The other method, the more usual one, at any rate at this season, is for the male to alight directly on to the back of the female, mating being accomplished amid much wing-beating. This method was always accompanied by an offering of food. I obtained no definite evidence of promiscuous mating, but on one occasion I saw the incubating bird, which to judge by the other nests would be the female, displaying to two other birds, which were perched close to the nest—the display was a mere fanning of the tail, which was turned in turn toward both of the birds present. On another occasion (at nest C) the female savagely attacked an intruder, which sat solici• tously on a bough near her head. The habit of Rooks to " mob " a mating pair has already been observed (E. Selous : Realities of Bird Life, Ch. IX.). On one of the three occasions when mating took place at nest A on March 27th two other Rooks appeared, but there was no proper mobbing, they merely cawed loudly to one another. (2) The Period during Incubation. So far as I can see the task of incubation falls entirely on the female. At any rate on the many occasions on which the male was present at the nest while the female flew off to stretch her wings, he never attempted to cover the eggs. The male feeds the female at fairly regular intervals, which seem to vary from nest to nest. At nests C and D, for instance, it was at least once every hour, but rather less at nest A and apparently very rarely at B. At another nest, however, it occurred as often as every half hour or thereabouts. To be fed thus by her mate is the cause of great excitement to the female. She frequently leaves the nest with anxious cawing to receive the food, and begs for it with a wildly excited wing flapping. She receives it amid contented " gobbling " sounds. Occasionally the male feeds her while she is sitting on the nest, but she usually leaves it and meets him half-way, though the actual feeding operation always took place on the nest itself. He either gives her food, or the female takes it out of his open gape. The latter method, which is the more usual, is shown fairly clearly in the photo• graph. Regurgitation costs no visible effort at all. The male alights and the feeding at once commences without any apparent " gulpings". The male is altogether a very attentive husband at this time, being constantly on the spot to watch over his mate. 32 BRITISH BIRDS. [VOL. XXVI. Not only does he feed her regularly, but he also gives her opportunities of easing her wings, which she does either by flying, or merely walking out on the boughs around and

Male Rook feeding female. Note the ecstatic position and quivering wings of the female. (Photographed by G. K. Yeates.) stretching her stiff wings and legs. On one occasion when the female was panting in the sun, the male came down and shielded her from the direct rays. Once settled she rarely turns the eggs, but she arranges them with great care before covering them and takes a very considerable time in getting them comfortable beneath her. (3) The Period after the Eggs are Hatched. When the young hatch the female eats the egg-shells. This I saw at nest C, and my friend, H. N. Southern, saw it occur again at nest A later in the week. The number of broken egg-shells beneath the trees during April seems to show that this is not always the case, though the wind may well take away a few. The hatching of the young at nest C was the VOL. xxvi.] BREEDING HABITS OF THE ROOK. 33 signal for the immediate departure of the female, and she returned in a very short space of time with the male, both cawing loudly. The female continues to brood constantly for over a week after hatching has taken place, and the visits of the male are now increased. At nest C feeding took place every 25 minutes almost regularly. The pouch is now fully distended with food, which was not the case when he had only the female to feed. His arrival is still greeted with excitement by the female and she now always flies off to meet him. Her solicitations for food are now redoubled and the male seems reluctant to give her any. He wears the expression of " I've got the food ; now I'm going to distribute it". Usually he flies to the nest before giving any to her (which he always did eventually). It is received now with the greatest ecstacy of flapping. The photograph shows such a scene. I thought at first that the female's request for food was in order to be able to assist in feeding the young herself, but it was clear that she wanted it for her own consumption and I never saw her feed the young. The male did aE the feeding of the young, at all events until they were over 13 days old. He also seemed responsible for clearing excreta, etc., from the nest. The female certainly never removed anything during my sessions in the hide. At the nest (save when the male is cleaning it out) the two birds appear to have their specified sides for alighting, and indeed it was difficult not to be struck by the cut-and-dried method of approach used by the females of all the nests watched. The same twigs, and almost the same part of those twigs, were used for each approach. (4) Some Miscellaneous Points. As with heronries, there appears to be a second occupation of a rookery. The first is that in which the eggs are laid about the second week in March, and the second is during the first week in April. On April 4th two nests were being built in my tree, one of which had eggs by April nth. When I took down my hide on April 17th a nest was being con• structed actually in the hide itself. So far as I could see there had been no casualties to nests in the rest of the rookery, so these were doubtless later breeders. The colony contained three vast clumps of nests. These on my first census were assessed at 5 or 6 nests, but on climbing to them later I discovered that two was the maximum number, the rest of the pile being but masses of the dead and rotten twigs of old nests. It is a point that may well be borne in mind by others taking a census of a rookery that these masses are more likely to be correctly estimated at two or three nests rather than five or six.