ETHOLOGICAL ASPECTS REGARDING THE BREEDING OF THE LONG-EARED OWL (ASIO OTUS L.)

Transcription

1 ETHOLOGICAL ASPECTS REGARDING THE BREEDING OF THE LONG-EARED OWL (ASIO OTUS L.) Emanuel TÂRNOVEANU Independent researcher, 88 Vasile Lupu Str., Bl. Z, 2 nd floor, , Iasi, Romania, emantarn@yahoo.com Abstract. This study aims to present some breeding aspects in long-eared owl (Asio otus L.) based on preliminary ethological observations made on five pairs of long-eared owls established in the Tătărași neighborhood (Iași, Iași County, Romania) during the years A first aspect taken into consideration concerns the relationship between this species and the corvids at the beginning of the breeding season, respectively in March, when it occupies the latter s nests in order to lay eggs. In spring 2014, we investigated the relations within the family group in the long-eared owl in the Tătărași Park while running an experiment of rehabilitation of a hand-reared juvenile. Separated accidentally from its family (which was nesting in the Copou neighborhood), on the 22 th of May 2014, the above mentioned juvenile acquired gradually the begging behaviour at meeting another family of long-eared owls in their nesting territory. The adequacy of the response to the new situation arising after fledging in this species occurred after five days, as the bird had relied on its hand-rearer initially. Our experiment resulted in mediating the adoption of the hand-reared juvenile by the local pair of long-eared owls. Its activity in the nesting area has been noticed for a long time, including the month of August. Once rehabilitated, the hand-reared juvenile followed its foster parents and their offspring in their foraging areas, the group occasionally returning to the Tătărași Park, where it was spotted by the specific calls. Usually the young would stay in the nesting area for 30 days, after which they would follow their parents out of the nesting territory. During the activity period at their nesting territory we recorded the food-begging calls of the fledged young both in Tătărași and in Copou (where the hand-reared juvenile came from). Keywords: territory, nest, calls, parents, adoption, flight Rezumat. Aspecte etologice privind reproducerea ciufului de pădure (Asio otus L.). Prezentul studiu urmărește să prezinte aspecte ale reproducerii ciufului de pădure (Asio otus L.) pornind de la observații etologice preliminare în cartierul Tătărași (Iași). În perioada anilor , am numărat cinci perechi de ciufi de pădure cuibărind în acest cartier. Un prim aspect luat în studiu privește relația ciufului de pădure cu corvidele, la începutul sezonului de reproducere respectiv în luna martie, când le ocupă cuiburile, pentru depunerea propriei ponte. În Parcul Tătărași, în primăvara anului 2014 am analizat comportamentul la ciuful de pădure sub aspectul relațiilor de familie. Totodată am desfășurat un experiment de reabilitare a unui juvenil provenind din cartierul Copou. Separat accidental de familie pe 22/05/2014, după părăsirea cuibului, acesta a fost pus în contact cu o familie de conspecifici din parcul mai sus menționat. Treptat el a ajuns să manifeste comportamentul de solicitare a hranei. Adecvarea răspunsului speciei studiate la situația experimentală s-a produs după cinci zile, cât a durat creșterea la mână. Experimentul nostru a avut ca rezultat adopția juvenilului reabilitat de către perechea de ciufi de pădure locală. Activitatea acesteia în proximitatea locului de cuibărit s-a înregistrat o perioadă îndelungată, luna august inclusiv. Momentul adopției a coincis cu atingerea fazei zborului. Grupul alcătuit din juvenilul reabilitat, părinții săi adoptivi și puii acestora l-am putut repera pe baza strigătelor specifice. Ocazional, păsările reveneau în parcul Tătărași din locurile de hrănire. De regulă, juvenilii stau în preajma cuibului 30 de zile, după care sunt hrăniți de părinți mai departe, pe raza teritoriului. În perioada de activitate în zona de cuibărit, noi am înregistrat strigătele de solicitare a hranei la juvenili în două zone verzi din Iași, cartierele Tătărași și Copou (de unde provenea exemplarul în cauză). Cuvinte cheie: teritoriu, cuib, vocalizări, părinți, adopție, zbor Introduction The study area is located in the proximity of two semi-natural habitats in the eastern part of Iași corresponding to two valleys. One of them is crossed by a chain of five

2 Emanuel Târnoveanu lakes among which three Ciric lakes and the other one belonging to the Bahlui river. The grasslands on the Bahlui riverside are followed by forest formations situated close to a row of buildings on the southern slope, while the Ciric area is fully forested (both on the eastern and the western slope). The alternation of stands of trees with grasslands corresponds to the ecological preferences of some species of rodents, that are part of the long-eared owl diet. The long-eared owls in our study have established both their winter roosting sites and the nesting territories in Tătărași, due to the availability of food resources in the proximity of the Ciric lakes, respectively the Bahlui river. Throughout the years , our observations have been focused on the following behavioral aspects in the population of long-eared owls in Tătărași: the preincubatory activities at the roosting site, the territoriality at the nesting site, the pairbonding, the relations within the family group, the movements of the families in the final stage of development in juveniles, and the reuse of the winter foraging routes at the beginning of autumn. The field research took into account particularly the relationship betweeen the long-eared owl and the corvids (Tome, 2003; Hadjisterkotis, 2003) while the former occupied the latter s nests during the breeding season. Data concerning the behavior of long-eared owl after fledging were collected in 2014 in a rook (Corvus frugilegus L.) colony in the western limit of the Tătărași Park (Ciurchi street). Material and Methods At first, in late February we spotted males of the studied species after their advertising-call on green spaces delimited by Vasile Lupu and Ciurchi streets, where the rooks build their nests in spring. The long-eared owl uses often the nests belonging to this species, which is one of the most representative corvids in town, in regards to its population size. Starting with the onset of the breeding season we also recorded females of the species under study after their calls in deserted rook nests. The alarm-call of the corvids at meeting the long-eared owl guided us to potential nesting territories of the latter. For the ethological observations we have also used the upper floors of some high buildings in the vicinity of which there are rook colonies used by the long-eared owl in the breeding season. For the illustration of the long-eared owl lifestyle in the nesting territories and of the young development phases (the molt) we used a digital camera Fujifilm FinePix HS20EXR (30 optical zoom, 16 Mpx effective resolution, maximum resolution, video resolution, SDHC external memory, 46 MB internal memory and image stabilizer). Some of the recordings at the nest in the spring of 2011 were made by climbing up the trees. This way we obtained data regarding the number of the eggs laid in the nest and the aspects appearing during the development in nestlings. In the case of the high trees with few branches growing from the base of the trunk or lacking branches in this region, we used either the safety climbing technique or the mountaineering equipment, or a pair of tree climbing spikes. The latter considerably increase the stability and the safety while working in the tree crowns. Few data have been collected this way, mostly biometric ones, since disturbing the long-eared owls in their roosting sites (the nesting territories in our case) is illegal. In regards to the clutch and the chicks, we investigated four active nests found in the rook colonies in Tătărași, respectively Copou. We did the majority of our field activities according to the ethological principles involving the familiarisation of the bird with the observer

3 The experiment of rehabilitation has been carried out in the long-eared owls nesting area in the Tătărași Park soon after the juveniles had left the nest. By means of tweezers we gave the hand-reared juvenile chicken meat-based food (necks and liver), on a small tree, once a day, at PM in the evening, for five days. Results and Discussion The long-eared owl does not build its own nest, it uses instead either the other birds nests or the squirrels dreys (Cramp & Perrins, 1994). At the beginning of the breeding season, in March, the male s advertising-call can be heard close to the corvids nests. Such vocalizations are the typical expression of the territoriality at meeting an intruder at the nest-site (Martínez et al., 2002) and actually the only form of intraspecific aggression (Cramp, 1998). We found in Iași pairs of long-eared owls breeding in rook colonies in green spaces in Copou, Păcurari, Tătărași, Podu Roș, Parc Sala Sporturilor and Antibiotics S.A. The population size in Tătărași was estimated at five pairs. One of them keeps using magpies nests (Pica pica L.) on the Ciric river bank, while the other four pairs are to be found in the rook colonies. At the beginning of the breeding season we noticed the competition for the occupancy of a nesting territory. During the early spring of 2011 we saw two pairs of longeared owls arriving simultaneously in a rook colony, passing from one nest to another and performing the wing-clapping display flight over the tree tops. At the same time we recorded the typical calls for the breeding season (on the 12 th of March 2011). The longeared owl emits such signals both to intimidate potential rivals and to attract mates (Johnsgard, 1988). At the onset of the breeding season, in the case of this strigid, the pairs roost during the daytime in the nesting territory (Pirovano et al., 2000). We noticed the allopreening, an activity typical for mates, in the roosting site of a pair of long-eared owls. The birds would allo-preen their head feathers while emitting squeaky calls. The male would bring food to its mate in response to such calls. During the nocturnal activity the long-eared owl would make swinging motions that have probably the same role as the vocalizations at the nesting territory in order to attract the mate. The male provides food for its mate throughout the incubation period (25-26 days) and during the development of the young until they reach the age of three weeks post-hatch and are ready to fledge (Cramp & Perrins, 1994; Fabrizio et al. 2008). The egg hatching is unsynchronized (Village, 1981), which determines post-hatch age differences between the siblings throughout their development. We pursued the female brooding the young at the nest by day. It protects the chicks to maintain the proper nest temperature and allo-preens them during the feathers formation. In the final stage of the young s development at the nest, while they were soliciting food by begging on branches, we have noticed how the parents were bringing prey to their offspring. The long-eared owl fledglings can hold food in their claws in order to eat it, once they are able to perch on the branches. The hunting period in the long-eared owl begins relatively early, after sunset, reaches its peak at midnight, followed by a period of rest after which, before dawn, a new hunting phase takes place (Johnsgard, 1988). During the family movements in the nesting territory we noticed the competition between the siblings for the access to the prey brought by their parents. During June and July we watched the long-eared owls from the Tătărași Park performing to-and-fro flights between

4 Emanuel Târnoveanu the valley of the Ciric chain of lakes, respectively the valley of the Bahlui river, and the nesting territory. These movements were related to the use of the trophic resource for the rearing of the young. Mention should be made that this strigid often establishes its nesting territories close to the open areas corresponding to its foraging ecological preferences (Rodríguez et al., 2006). If there is no abandoned nest within reach, the long-eared owl would drive away the birds similar in size to itself from their own nest. We met such a case in the mid-march of 2011 while monitoring a rook colony. The nest would be usurped in an aggressive manner. The female long-eared owl would perform simulated attacks on the rook which would aim for the neck. By that time, in the study area, a high incidence rate of nest desertion took place in the rook population during the sexual activity in the long-eared owl. The interference between the two species of birds is limited to the onset of the breeding season in the long-eared owl, while the strigid is looking for a nest. Regarding the particular adoption case of the hand-reared juvenile in the Tătărași Park, we recorded some tonal differences in the food-begging calls, compared to those of the local young. A plausible explanation might be the familiarity with the hand-rearer. At the beginning of our experiment we provided all the necessary food for the rehabilitated bird untill it was adopted. We recorded the tonal particularity of those vocalizations for the first time at meeting the hand-rearer in the last day, when the interference with that bird was still possible (the 25 th of May 2014). After having been adopted, the subject of our experiment joined the family group of long-eared owls in the canopy, undertaking their behavioral pattern in all respects including the movements outside the nesting territory. The fall from the branches of the large young might be caused either by their avoidance to encounter predators or by their failed attempt to jump from one tree to another (Rodríguez et al., 2006). If the young cannot climb on branches soon they are exposed to predation or to human intervention, often unjustified, as in this case. This is one of the reasons we have rehabilitated the juvenile concerned that had been caught and kept as a pet by a pauper. We have foreseen, at the same time, the risk of the young being hit by a vehicle, the nesting site to which the juvenile belonged being situated in the proximity of a road. Our rehabilitation experiment resulted in the adoption of the hand-reared juvenile in a quieter semi-natural habitat, away from traffic, with easy access to small richly branched trees such as those in the Tătărași Park. Conclusions The living conditions of the long-eared owls in Tătărași enable the breeding success, as our ethological and ecological data show. The presence of the corvid populations (rooks and magpies) breeding inside Iași enables the long-eared owl s breeding since this species uses mainly the open nests built by other species of birds. The relationship between this strigid and the rook is notable by the aggressive nature of the former. This type of relationship is maintained only during the early breeding season, when the female seeks an available rook nest for laying eggs. Otherwise, the adults of both species, similar in size and with a similar agressive potential, would cohabit without interfering in the nesting territory. While soliciting food by begging, the juvenile long-eared owls compete for the prey brought by their parents. The hand-reared juvenile was found by night and day in the

5 nesting territory of the foster family all along two months, which proves that it had not only been protected but also fed by its foster parents, as was the case with their own offspring. There is probably a connection between the foster parents response and the foodbegging calls of the juvenile in our study, which had been initially directed to the handrearer. The advanced age at which that juvenile was rehabilitated (nearly three weeks) is less permeable to imprinting on the human, which explains the delay of the positive response to the hand-rearer, materialized in the begging display. The variety of the ecosystems with optimum productivity and favorable climate conditions in the study area explains the success of our rehabilitation experiment in the long-eared owl breeding season in References Cramp, S., Perrins, C. M., The birds of the Western Palearctic, Vol. 8. Oxford University Press, Oxford, U.K. Cramp, S., The Complete Birds of the Western Palaearctic on CD-ROM. Oxford University Press, Oxford. Fabrizio, S., Luigi, M., Paolo, P., Density, diet and productivity of Long-eared Owls Asio otus in the Italian Alps: the importance of Microtus voles: Capsule Relatively large populations, feeding predominantly upon voles, were present at higher elevations. Bird Study, 55(3), Hadjisterkotis, E., The effect of corvid shooting on the populations of owls, kestrels and cuckoos in Cyprus, with notes on corvid diet. Zeitschrift Fur Jagdwissenschaft, 49: Johnsgard, P. A., North American Owls: Biology and Natural History. Paul Johnsgard Collection. Paper 46 Martínez, J. A., Zuberogoitia, Í., Colás, J., Macía, J., Use of recorder calls for detecting Long-eared owls Asio otus. Ardeola, 49 (1): Pirovano, A., Rubolini, D., De Michelis, S., Winter roost occupancy and behaviour at evening departure of urban long-eared owls. Italian Journal of Zoology, 67(1): Rodríguez, A., Garcia, A. M., Cervera, F., Palacios, V., Landscape and anti-predation determinants of nestsite selection, nest distribution and productivity in a Mediterranean population of Long-eared Owls Asio otus. Ibis, 148: Tome, D., Nest site selection and predation driven despotic distribution of breeding long-eared owls Asio otus. Journal of Avian Biology, 34: Village, A., The diet and breeding of Long-eared Owls in relation to vole numbers. Bird Study, 28(3):