Analele Științifice ale Universității Alexandru Ioan Cuza din Iași, s. Biologie animală, Tom LIX, 2013 ETHOLOGICAL STUDY OF THE ROOK (CORVUS FRUGILEGUS L.) IN THE WILD AND IN SEMI-CAPTIVITY Emanuel TÂRNOVEANU Faculty of Biology, Alexandru Ioan Cuza University of Iași, B-dul Carol I, no. 20A, 700505 Iași, Romania, emantarn@yahoo.com Abstract. The aspects under study in this paper refer to reproductive activity, feeding, roosting, behaviour of the rook in nature and in circumstances of semi-captivity. In Tătărași (Iași), starting with spring 2011 we carried out observations in 10 rook nests, focusing on the following aspects: copulation, laying the eggs, incubation, hatching, post-embryonic development and fledging. In 2010, we experimentally kept 5 fledglings in semi-captivity and we fed them with a varied diet, following their eating preferences. We ve already mentioned this experiment in the 57 issue of Scientific Annals of Alexandru Ioan Cuza University of Iași. Many fledglings starve in case of falling off the branch, because parents usually stop providing them food. Only healthy individuals are taken care of. As an element of scientific novelty in the spring of 2012 we have recorded for the first time a case in which the parents adapted to the youngster s weak flying abilities by feeding it in the lower part of the tree. Keywords: behaviour, pairs, food, insects, field. Rezumat. Studiu etologic despre cioara de semănătură (Corvus frugilegus L.) în natură și în semicaptivitate. Aspectele abordate în prezenta lucrare sunt: activitatea de cuibărit, hrănirea, înnoptarea, comportamentul ciorii de semănătură în natură și în condiții de semicaptivitate. În Tătărași (Iași), începând cu primăvara anului 2011, am efectuat observații la 10 cuiburi de cioară de semănătură pentru a surprinde: copulația, depunerea pontei, incubația, ecloziunea puilor, dezvoltarea postembrionară și emanciparea puilor. În anul 2010 am crescut experimental, în captivitate, 5 pui zburători, pe care i-am hrănit variat, urmărindu-le preferințele alimentare. Referirile la experimentul în cauză apar în tomul 57 al Analelor Științifice ale Universității Alexandru Ioan Cuza din Iași. Puii zburători căzuți de pe ramuri mor de foame, în cele mai multe cazuri, întrucât părinții de regulă nu-i mai hrănesc. Doar exemplarele sănătoase sunt îngrijite. Ca un element de noutate științifică, în primăvara anului 2012 am înregistrat pentru prima dată adecvarea la semnalele unui pui cu capacitate slabă de zbor a răspunsului parental hrănirea sa în porțiunea bazală a coronamentului. Cuvinte cheie: comportament, perechi, hrană, insecte, câmp. Introduction The rook is a sinantropic bird which finds its food and roosting or breeding ground in the vicinity of cities or towns. The biological cycle of the rook was recorded in the colony in Tătărași district (Iași), and the aspects under observation were: pair-bonding, building the nest, copulation, duration of laying the eggs, duration of incubation, post embryonic development and young fledging. The rehabilitated young birds interact well with humans, which makes it possible to raise them in semi-captivity. Material and Methods Rook data, gathered in the study area, have been synthesized in a report and supported by images. In order to take fixed images and films we used a digital camera Fujifilm FinePix HS20EXR, a digital video recorder Panasonic SDR-H80 SD/HDD, together with a tripod T nb FTDC034880. The ethologic observations at the breeding place were carried out from block terraces on Vasile Lupu Street (Iași). The study of the feeding - 77 -
Târnoveanu Emanuel activity was carried out primarily on Bahlui alluvial field (Iași). In order to study the rook roosting behaviour we carried out observations on Carol I Avenue and in Anastasie Fătu Botanical Garden of Iași. Results and Discussion The breeding activity starts with territorial fights between the members of the colony. The individuals dispute the nests by attempts at mutual intimidation, manifested through shrieks and pinching (Fig. 1). Figure 1. Battle between adults for occupying an old nest (original). The behaviours which is important in the formation of the pairs is the courtshipfeeding (Fig. 2). Figure 2. Food transfer between mates (original). - 78 -
Analele Științifice ale Universității Alexandru Ioan Cuza din Iași, s. Biologie animală, Tom LIX, 2013 After the pairs are formed, the rooks begin building the nest, mating and defending their territory. In spring, in March or April, rooks build or repair their old nests. They use tree branches (Fig. 3), grass, dirt, feathers as materials. The nest-building activity is marked by food-begging calls from the female. These acoustic signals are associated only with breeding (Perrins & Cramp, 1998). The finalization of the nest building usually takes place in the second decade of March. Figure 3. Nest building from vegetable material (original). In view of copulation, the male attracts the female by means of a series of movements bowing, opening the wings, tail-fanning, advancing towards the female. The female s sexual responsiveness may be deduced from a combination of gestures shaking the tail and opening the wings. The copulation lasts for 10 to 13 seconds, in which time the male vigorously flaps his wings (Perrins & Cramp, 1998). The courtship display followed by copulation is possible in trees (Fig. 4) or on the ground (Fig. 5). Figure 4. Courtship displayed in the canopy (original). Figure 5. Courtship displayed on the ground (original). - 79 -
Târnoveanu Emanuel The female lays the first egg a few days after finishing the nest, in the reclining part of the nest (Fig. 6). The number of the eggs may vary between 1 and 6. In case of destruction of the initial clutch, the female may lay a new series of a maximum of 3 eggs(replacement clutch). Incubating the eggs lasts 16 to 18 days and the female begins to transfer heat to the clutch after laying the first 2 eggs. The female food-begging calls are usually more intense after laying the eggs. Figure 6. Freshly laid egg (original). Hatching takes place along 2-3 days. The egg shells are partly eaten by the female after hatching and later removed from the nest. In 2011, from a total of 18 eggs distributed among 5 nests, the first chicks to hatch did so on April 20th. The male brings food to the family, helps sanitize the nest and defend the chicks. While the nest is being used, parents feed chicks invertebrates, fruit and cereal grain. 40 days after the hatching the young birds leave the nest, but stay in the care of the parents for other 5-6 weeks (Perrins &Cramp, 1998). In the first few days after leaving the nest, the fledglings can only fly for short distances and receive food from their parents in the canopy. The typical sounds for food requirement are high pitched, long and slightly shaky. Any young falling to ground are ignored and therefore doomed (Cătuneanu, 1953; Røskaft & Slagsvold, 1985; Perrins & Cramp, 1998). However, we have recorded a case in which the parents adapted to the fledgling s weak flying abilities by feeding it in the lower part of the canopy (Fig. 7). The analyzed parental behaviour was carried out in unusual conditions, which constitutes an element of scientific novelty. In Tătărași colony we observed 21 chicks (distributed in 16 nests) out of which only 11 reached fledging. Once the development of the plumage is completed, flights above fields and plantations of seasonal fruit trees (cherry trees, mulberry trees) start. In such places parents teach the fledglings how to get food and feed them at the same time. Both parents look after the youngsters after they start flying (Fig. 8). The rook displays a gregarious way of life all through the year (Perrins & Cramp, 1998). In the cold season and at the beginning of spring it joins bevies with the jackdaw (Fig. 9). - 80 -
Analele Științifice ale Universității Alexandru Ioan Cuza din Iași, s. Biologie animală, Tom LIX, 2013 Figure 7. Fledgling rook perched in the lower part of the canopy (original). Figure 8. Family group on the feeding ground (original). Figure 9. Rooks and jackdaws feeding in a mixed flock, in Tătărași district (original). - 81 -
Târnoveanu Emanuel The rook bevies use the tree branches and the roofs or terraces of buildings to roost. During breeding season, rook males look for food alone or in small groups. In summer, after the flight from the colony, the youngsters join their parents to the feeding grounds, where they will follow until the end of summer. In autumn, youngsters are separated from adult population. They make pairs during the first autumn and are ready to breed after 2 years old. These birds usually spend their day in open spaces, and in the evening come to the roosts after a series of curvatures above the trees. In December 8th, 2010 we noticed a concentration of over 80 individuals in a feeding ground in Tătărași district. In Iași, there are winter roosts in several areas: next to Prefectura, in a square of plane trees, in the Titu Maiorescu student campus and its surroundings towards the west, in the Grădina Copou, in the lime trees along Carol I Avenue, in the southern sector of the Botanical Garden and in Păcurari district. In the agglomerations formed on trees at night, one can notice a vertical stratification of the birds according to age (Cramp & Perrins, 1994). The adults occupy the upper and the youngsters occupy the lower part of the tree. The species under study expresses alarm in different ways, when it is scared or disturbed. Panic at meeting man within its feeding grounds is expressed by means of precipitated gestures such as running, grabbing and throwing food, displaying open beak and fanned tail, at the same time as emitting alarm calls. In case the nest is disturbed, the rooks emit alarm calls and hit the branches with their beak at the same time (Stănescu, 1973). Simulations of in-flight attacks are observed when a predator enters the territory. When a carnivore (a cat for example) comes within the range of a fledgling, adults automatically highlight the warning behaviour. In trees, squirrels are driven away with warning sounds. The rook is usually cautious about human contact, but allows close observations from humans in winter when it has limited access to food. During breeding season the pairs of the long eared owl (Asio otus) look for the breeding grounds of rooks and drive away the birds they meet in the nests. The rook emits warning signals in such situations and usually leaves the nest. At the same time, the rook swells its feathers and simulates attacks in the direction of the intruder (Fig. 10). When eggs are laid by the long eared owl, its activity of looking for nests stops and the two species of birds cease interacting. Rook nests used by the long eared owl have been found in five breeding grounds in Iași city. Figure 10. The alarm posture adopted at meeting long-eared owl (original). - 82 -
Analele Științifice ale Universității Alexandru Ioan Cuza din Iași, s. Biologie animală, Tom LIX, 2013 Behaviour of rehabilitated fledglings Looking after fledglings may be carried out in an outdoor aviary, on a balcony or in an open space with natural vegetation shade. The rehabilitated youngsters are easily tamed and recognize their care taker, even when raised in open spaces (Fig. 11). They have to be hand reared for a very long time, until their second moult (August), when they become able to feed themselves. Figure 11. Young rookraised in semi-captivity (original). In ethologic experiments carried out on rehabilitated youngsters, we noticed the decreasing dependence on the care taker as the moult process advances. The decrease of food begging in the Corvus frugilegus youngster at the stage of immature plumage development is an original fact observed by us. Generally speaking, birds prefer to perch on the upper part of the canopy or buildings, where they feel safe. They take their first flying exercises on short distances, and later they learn the spatial landmarks of the raising ground and will explore neighbouring areas too. In order to follow their kind in the wilderness, they emit sounds and execute curvatures in order to evoke the start of the journey. In nature fledglings raised by parents receive insects hunted in the field (for example crickets), as is fit for the need of food based on animal protein. We fed the 5 fledglings kept in semi-captivity in 2010 with a varied diet, following their eating preferences. Meat was preferred to eggs and cheese. Among insects, they preferred orthopters. Of vegetarian food, they chose green beans, oat flakes, a series of fruit and vegetables and did not refuse mushrooms either. They displayed great pleasure in eating walnuts. Conclusions In the hot season, the rook finds food (insects and seeds) in the alluvial plain of rivers. Forming bevies to search for food starts in summer, after the young flies from the nest. Generally speaking, juveniles form smaller bevies than adults. The rook associates with the jackdaw in all seasons. When roosting, adults occupy the upper parts of the tree, whereas the youngsters stay in the lower parts. Defence from the enemy is done by alarm calls, emitted both from a fixed location (tree, ground) and in flight. When an enemy is present in the colony, rooks use to hit the branches with their beaks. - 83 -
Târnoveanu Emanuel Conflicts between the rook and the long eared owl are manifest during the early breeding season, when the long eared owl is looking for available corvids nests to lay the eggs. The new aspects of our study refer to the behaviour of brooding young after fledging and the characteristics of raising fledglings in semi-captivity. Fledglings raised in semi-captivity need a rich animal protein diet, but also appreciate vegetables, fruits, seeds. Their tendency to go back to nature is manifest both by sounds and by curvatures above the location where they were raised. Acknowledgements To research activities that are the subject of this article were carried out with financial support POSDRU/88/1.5/S/47646 project, financed by European Social Fund, the Human Resources Development Operational Programme 2007 2013. References Cătuneanu, I. I., 1953. Ciorile și celelalte corvide: metodele de combatere a celor dăunătoare. Editura Agro- Silvică de Stat, București. Cramp, S., Perrins, C. M., 1994. Handbook of the Birds of Europe, the Middle East and North Africa, 8. Oxford University Press, Oxford. Perrins, C., Cramp, S., 1998. The complete birds of the western Palaearctic on CD-ROM. Oxford University Press, Oxford. Røskaft, E., Slagsvold, T., 1985. Differential Mortality of Male and Female Offspring in Experimentally Manipulated Broods of the Rook (Corvus frugilegus). J. Animal Ecol., 54 (1): 261 266. Stănescu, D., 1973. Agresivitate și moderare la Corvus frugilegus L.1758 în timpul deranjării cuibăritului. Studii și com. St.nat., Muz. Brukenthal, Sibiu, 16: 301 318. - 84 -