ETHOLOGICAL ASPECTS OF CAPTIVE ROOK CORVUS FRUGILEGUS (L.)

Analele Științifice ale Universității Al. I. Cuza Iași, s. Biologie animală, Tom LVII, 2011 ETHOLOGICAL ASPECTS OF CAPTIVE ROOK CORVUS FRUGILEGUS (L.) Emanuel TÂRNOVEANU Alexandru Ioan Cuza University of Iași, Faculty of Biology, B-dul Carol I, 20 A, 700505, Iași, emantarn@yahoo.com Abstract. From a systematic point of view, the rook, [Corvus frugilegus (L.)] is part of the family of Corvids, the Passeriformes class. We captured five juveniles from the wild that we kept in captivity in an aviary of wood and Rabiț net placed in a backyard near the Ciric forest. I observed the feeding behaviour and the cohabitation in a narrow space. The feeding of the juveniles was made four times a day, the food consisting in meat, eggs, cereals, bread, fruits and vegetables. Regarding the preferences for certain type of food, I noticed that the vegetables (the cabbage, the potatoes, the cucumber, the beans and the marrow) are among the favourites and some fruits also (the cherries, the mulberries, the common elder s fruits, the raisins, the blackberries, the wax cherries, the plums, the apples, the water melon) and other fruits (the peaches, the apricots, the sweet cherries) are less appreciated or refused. I also noticed the tendency of hiding the aliments in the clefts of the ground. As regarding the cohabitation I observed a positive interaction between the members of a group of individuals that was formed immediately after they were captured from the wild, and signs of hostility or reservation between those and a recently came neighbour. The peaceful cohabitation was possible due to the fact that the initial group members were gathered together in a coiled up position, for allowing the social interaction and allopreening. Keywords: aliment, shelter, captivity, digging the ground, gestures Rezumat. Aspecte de etologie la cioara de semănătură, Corvus frugilegus (L.), în condiții de captivitate. Din punct de vedere sistematic, cioara de semănătură [Corvus frugilegus (L.)], aparține familiei Corvidae, ordinul Passeriformes. Din natură am capturat cinci juvenili de C. frugilegus pe care i-am ținut în captivitate, într-o volieră construită din lemn și plasă Rabiț amplasată într-o curte din apropierea Pădurii Ciric. Am urmărit comportamentul alimentar și coabitarea în spațiu limitat. Hrănirea juvenililor s-a făcut de patru ori pe zi, hrana fiind constituită din carne, ouă, brânză, cereale, pâine, legume și fructe. În ce privește preferendumul față de un anumit tip de hrană, am constatat că legumele, (varza, cartoful, castravetele, fasolea, dovlecelul), sunt preferate, de asemenea, unele fructe (vișinele, dudele, bobițele de soc, strugurii, murele, corcodușele, prunele, merele, pepenele verde), iar alte fructe (piersicile, caisele, cireșele) sunt mai puțin apreciate sau refuzate. Am observat comportamentul de ascundere a alimentelor în sol, în crăpături. În ce privește coabitarea am observat o interacțiune pozitivă între subiecții dintr-un grup format imediat după capturarea din teren, și una de ostilitate sau rezervată între aceștia și un seamăn nou introdus. Coabitarea pașnică s-a putut înregistra în contextul alăturării membrilor grupului inițial, într-o postură ghemuită, în vederea toaletării sociale. Cuvinte cheie: aliment, adăpostire, captivitate, săparea solului, gesturi Introduction Having a single moment for laying eggs in one year, the rook (Corvus frugilegus) uses the nesting colonies for reproduction only during the spring season and on the beginning of the summer. In the autumn, the nuptial parade takes place and the birds begin to use again their nests. Without following a complete reproductive cycle, they keep visiting the nests regularly, during winter season. The objects of the present study, ethological oriented, are the emancipation aspects the last stage in the reproductive cycle of the Corvus frugilegus species. The behaviour range typical for juveniles was investigated in the context of pseudo-taming of five individuals. Those birds constituted biological material by the time they get young, when they started to show social gestures and sound signals in order to get into contact with the wild, local rooks. During the growing up process the feathering moult took place and the iris colour changed from light blue to grey with brownish nuances. - 91 -

Emanuel Târnoveanu Material and methods The ethological studies on Corvus frugilegus species observed in captivity were realised between the 15 th of May 2010 and 27 th of July 2010. The origin area of the five young specimens is located in the northern part of the city of Iași, along the Boulevard Carol I, where important concentrations of nesting couple of birds can be encountered. The nesting preference emphasised, preponderantly, in the green areas between the building of the Romanian Academy Iași branch and the Super Copou Store, with big, old trees. In order to comply with the aims of ethological research of the rook in captivity, the individuals juveniles of 32 days old were tamed using the method called feeding from hand. Their food consisted on cheese, boiled eggs, chicken gizzards, fruits (mulberries, cherries and summer apples), vegetables (cucumbers, cabbage, salad, potatoes, and long pod beans), cereals and bread. The birds were kept in an aviary made of wood and Rabiț net, having 3.5 m in length, 2.5 m wide and 2 m high (Fig. 1). As a refuge the birds have at their disposal a cage made of wooden boards and Rabiț net, 115 cm in length, 78.5 cm wide and 100 cm high and placed on the ground (Fig. 2). Both the aviary and the cage were equipped with resting accessories (slats and branches) and food and water containers (glass and porcelain vessels). As a bath tub the birds received a plastic 2 litre basin. In order to record images we used a LUMIX DMC-FZ35 Panasonic photo camera, with an angle of 27 mm wide, 18x optic zoom and LEICA DC lens with F2.8 brightness. Figure 1. Wooden and Rabiț net aviary used for taking care of captive rook. Figure 2. Cage made of wood and Rabiț net for sheltering the captive rook. Results and discussions On 15 th of May 2010 the Corvus frugilegus juveniles encountered in the wild had their growth feathers incomplete. That was the reason for which they could not fly (Fig. 3). Their eyes presented a blue colour; their beaks had partially black pigmentation. The flight feathers, made of remiges and retrices, remain unchanged till the adult age, i.e. 2 years old (Richards, 1976a). Post juvenile moult takes place from summer till autumn, inclusive September, to be more precise and regards only the cover feathers, with metallic reflexes (Fig. 4). The buccal colour in adult birds is dark grey, in juveniles is pink. In the case of juveniles, the tongue, the palatine veil and the buccal floor acquire dark spots during the moult process. That is also when the colour of their eyes changes, from a greyish blue to brown (Dunnet et al., 1971). Our observations over the moult process emphasise the fact that the sense of growth of replacement feathers is from the ventral plan to the dorsal one. First the moult of the body occurs, than of the head, and finally the moult of the posterior neck occurs. - 92 -

Analele Științifice ale Universității Al. I. Cuza Iași, s. Biologie animală, Tom LVII, 2011 Figure 3. Juvenile of the Corvus frugilegus species, with the growth feathers incomplete. Figure 4. Young rook, Corvus frugilegus species individual, after post-juvenile moult. In case of the Corvus frugilegus juveniles, the typical method of displaying the stimulation of food searching behaviour of the parents consist in uttering long, strong, nasal cries and in trembling wing gestures (Fig. 5). Figure 5. Manifestations of the juveniles while soliciting food: the wings are trembling and the beak is wide open. - 93 -

Emanuel Târnoveanu We recorded, in pseudo-taming circumstances (Cociu, 1999), the domination of high inflexions in the voice of the subjects, different from the natural ones, which can be corroborated with the absence of the wing trembling. The juveniles show the food solicitation posture when they encounter themselves in the presence of the keeper. The sounds used for establishing contact inside the group, had, by comparison, a solemn tonality. While the sounds were uttered, some ritual gestures were noticed bowing the head, filling the interclavicular air sac, swelling the feathers of the neck, spreading out the tail and striking the ground with their beak actions that were performed while walking as well as while staying. Subsequent to the above-mentioned gestures, the couple cohabitation behaviour model was established, generally concretized by gestures of preening the feathers of the partner, also known as allopreening (or mutual preening) and by food soliciting (Richards, 1976b). Nevertheless, the component of the food transfer was not observed. To the sounds uttered by other wild rooks that were flying above the aviary, the subjects responded with long cries, according the behaviour pattern of reference to their parents. On the 5 th of June 2010 one of the juveniles died and it was replaced with another. The hostile reaction of the subjects of the initial group towards the new comer bird that appeared at that date manifested through lowering their heads and ruffling the dorsal feathers. Subsequently, gestures of submission to the new comer rook were noticed, and they were materialized by hissing while laid on a side. The most intense conflicts were observed when the rival birds were frontally exposed in the narrow space of the sheltering cage. In the conditions of feeding together those five rooks, the tendency of depriving the new came bird of its portion by one of the individuals from the initial group was observed. When leaving the nest, around 32 days old, the juveniles had reduced motility. At the beginning of the emancipation period, they fly short distances, from one branch to another, or between two close trees, inside the colony, where they wait for their parents to bring the food. During the last two nesting weeks their flight feathers develop, which allows them to fly actively, near their parents, in search for food. Initially, the juveniles eat preponderantly fruit, but later on they learn to catch invertebrate creatures such as caterpillar, spiders etc. By digging the spongy ground, with its beak, the rook locates earthworms, in their galleries (Lockie, 1956). Inside the aviary the pseudo-tamed rooks dig out species like Lumbricus and Allolobophora. In case of Corvus frugilegus species, the feeding behaviour includes keeping the aliments with its foot and dividing it into fragments in order to eat it, by moving and clacking its beak. By doing this the rook removes the fruits husks and the nuts shells. The Corvus frugilegus species is omnivorous with granivore prevalence (Comănescu, 1997). Once the rook soothes its hunger, the bird transports the food remainders, on its beak, or in a sublingual enlargement, in order to deposits it in the litter or among the blades of grass that cover the ground in order to eat it later. From the food motivated actions we noticed the active search for invertebrates in the vegetation or in the ground (by digging) and hiding the food deposits in the litter. In the wild, Corvus frugilegus eats the eggs and chicks of the collared dove (Streptopelia decaocto). The collared dove harasses the rook when spots it on its nesting territory in order to force it to retreat. The Corvus frugilegus juveniles we looked after were once attacked by a collared dove (Streptopelia decaocto) on the roof of the aviary, according to this strategy of defending the nest. The periods of activity during the day alternate with resting and sleeping periods. Each two hours the juveniles were fed and allowed to explore the environment; these moments were followed by sequences of sleep when they perch on one leg, on a suspended support (tree, building). - 94 -

Analele Științifice ale Universității Al. I. Cuza Iași, s. Biologie animală, Tom LVII, 2011 During the resting periods, rooks regurgitate pellets (Czarnecka & Kitowski, 2010), containing remains of undigested food (skin and husks from fruits, leaf nervures, cereal hulls) and little rocks. The cloudy weather has a negative influence on the activity of the rook, because food consumption is reduced. During hot summer days rooks get themselves wet by means of vigorous shaking movements of the head and wings in the water. The bathing is not continuous; the birds return to the dry ground from time to time and smooth out or arrange their feathers with their beak and claws. Rubbing the eyes against the wing is part of this behaviour register. When the bird is scratching, the eyes are protected from the claws by the nictitant membrane. When it rains the birds use the secretion produced by the uropygial gland; they spread it with the beak and lubricate the entire body with the help of specific wing movements in order to get their feathers impermeable. On a sunny day, when they tend to overheat, rooks open their beaks and hold their wings down and away in order to refresh themselves. Besides the dipsic behaviour (Acatincăi, 2003) we noticed that when the rooks used the water trough for drinking water, the food was dipped and agitated in a ludic manner. Non alimentary materials like lumps of earth, litter fragments and even undigested food were dipped in the water. The ingestion of pulverizing material was sustained by drinking water; this made the deglutition much easier. Together with the water tiny fragments of old bricks were swallowed. From ludic behaviour repertoire I noticed branch grasping; the branches were then introduced inside the refuge cage, being assimilated to a nesting space. In captivity, Corvus frugilegus develops a special curiosity towards the opening and closing system of the cage, which it controls with the help of its beak. Surveying territory gestures appeared together with the tendency of nocturnal movement in order to identify fellow rooks flying to the gathering places for sleep large green areas with big trees, in the northern part of the city of Iași ( Anastasie Fătu Botanical Garden). The flight of the rook is noisy as a consequence of the wings vibration. After being released (on 23 rd of July 2010), the rooks demonstrated efficiency and spontaneity in flight. Although they were free to go the birds continued to turn back to the aviary in which they were taken care of for 4 days. After that they returned to the wild. The final departure was preceded by a circular flight over the trees situated near our aviary. In our opinion that flight was in a certain manner a sign of communication with the keeper whom the pseudo-tamed rooks became considerably attached. The attachment was conditioned by the constant feeding. In the context of retreat flights for sleep, in the evening, the wild rooks demonstrate a tendency to always relate to their nesting areas, by rotating in the air. In case of our experiment, the aviary where they were looked after resembled with a nesting colony (27 th of July 2010). Conclusions During the emancipation period the Corvus frugilegus juveniles presented distinctive signs to be recognized in the field: their feathers moulted, they flew shorter distances comparing to the adult birds, they showed a special curiosity when exploring, they preferred fruits and the food dipped in the water, they introduced in their ludic behaviour the nest building component, they followed the adult birds during the nights displacements, interacted by means of allopreening and by means of food solicitation, as a group and individually (one from another). The ethological aspects that relate to emancipation would have been impossible to observe in natural conditions because they are not precisely located in a certain territory; the rooks are adopting a wandering life style when leaving their colonies. - 95 -

Emanuel Târnoveanu 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 Acatincăi, S., 2003. Etologie: Comportamentul animalelor domestice, Editura EUROBIT, Timișoara. Comănescu, G., 1997. Elemente de morfologie animală. Tractusul digestiv la păsări, Editura Universității Alexandru Ioan Cuza Iași. Czarnecka, J., Kitowski, I., 2010. Seed dispersal by the rook Corvus frugilegus L. in agricultural landscape mechanisms and ecological importance. Polish Journal of Ecology, 58 (3): 511-523. Cociu, M., 1999. Etologie. Comportamentul animal, Editura All, București. Dunnet, G.M., Fordham, R.A., Patterson, I.J., 1971. Ecological studies of the rook (Corvus frugilegus L.) in north-east Scotland. Proportion and distribution of young in the population. Journal of Applied Ecology, 8 (3): 815-833. Lockie, J.D., 1956. The Food and Feeding Behaviour of the Jackdaw, Rook and Carrion Crow. Journal of Animal Ecology, 25 (2): 421-428. Richards, P.R., 1976a. The Onset of Moult in the Rook. Bird Study, 23 (3): 212. Richards, P.R., 1976b. Pair Formation and Pair Bond in Captive Rooks. Bird Study, 23 (3): 207-211. - 96 -