COMPARATIVE ANALYSIS OF LONG-EARED OWL ( ASIO OTUS ) WINTER DIET FROM TWO EUROPEAN CITIES – CHISINAU (REPUBLIC OF MOLDOVA) AND BACAU (ROMANIA)

One Health and Risk Management Nr. 1 / 2020 / ISSN 2587-3458 / ISSNe 2587-3466 Disponibil online 4 April, 2020. Descarcări-12. Vizualizări-51 ----------------------------------------------------------------------------------------------------------------------------------Geographical clines in the size of the herb field mouse (Apodemus uralensis) Balciauskas Linas1, Amshokova Albina Kh2, Balciauskiene Laima1, Benedek Ana Maria3, Cichocki Jan4, Csanady Alexander5, de Mendonca Philippe Gil6, Nistreanu Victoria7 1 Nature Research Centre, Vilnius, 2 Tembotov Institute of Ecology of Mountain Territories RAS, 3 Lucian Blaga University Sibiu, 4 University of Zielona Gora, 5 University of Presov, 6 University of Lisbon, 7 Institute of Zoology


INTRODUCTION
Many of the rodent species are important pests of agricultural crops and cereal deposits, including urban areas. The nocturnal prey birds are regulatory species that contribute to maintaining rodent density at more or less constant level. The long-eared owl (Asio otus L.) is a sedentary bird and one of the most widespread in Europe (1)(2)(3)(4)(5). During the winter period the density of species increases on the account of the migrant individuals from the northern regions and they form colonies of several tens of individuals. In most cases, the owls prefer to winter each year in the same place. The hunting sectors of the long-eared owl are open type biotopes, where they mainly hunt rodents and occasionally birds, shrews and bats. Following the digestion process, the prey birds regurgitate the indigestible remnants of eaten a-nimals (bones, hair, feathers, fur) in the form of pellets. The pellets analysis can provide important data regarding the feeding regime of the bird, the fauna of small mammals in a certain area, their density and their seasonal and annual dynamics, etc. The long-eared owl is well adapted to anthropic environment and its wintering colonies are frequently registered in urban localities (4).
The long-eared owl is a feeding specialist predator and not all species are equally hunted prey. The attractiveness of a prey species depends on specific qualities, the most important of which is the size (1). The long-eared owl shows strong preference for Microtus voles across Europe, but in urban areas it hunts in open type biotopes outside the city and/or use alternative prey (27). In winter, A. otus is capable to localize the prey under a snow cover of 40-50 cm (14). As adaptations of winter diet to urban environment can be considered the use of higher ratio of synanthropic rodent species (Mus musculus, Rattus norvegicus), of bird species as well as more diverse trophic spectrum (4,24,(28)(29)(30)(31)(32)(33).
The aim of the paper is to perform a comparative analysis of long-eared owl winter diet in two European cities, Chisinau and Bacau, with similar environmental -climatic conditions and rather different anthropic impact, in order to emphasize the similarities and the differences.

MATERIAL AND METHODS
The studies were performed in winter periods of 2011-2012 and 2012-2013 in Chisinau and Bacau cities. Chisinau is a large city with the surface of 123 km 2 , situated in the central part of the Republic of Moldova at the altitude of 82 m, coordinates 47001ꞌ N 28052ꞌ E. Bacau city is the major city of Bacau county, with the surface of 43.19 km 2 , situated in eastern part of Romania at the altitude of 165 m, coordinates 46035ꞌ N 26055ꞌ E. The climate of both cities is humid continental with warm summers and cool, windy winters. The winter period lasts 78-80 days. The average temperature in winter is -2.3°C in Chisinau and -4 C in Bacau city, while the minimum temperature in January and February can drop below -20°C.
In Chisinau city a colony of long-eared owl (Asio otus L.) of 38 individuals was located in a courtyard of a school from Ciocana district with several dozens of tall coniferous and deciduous trees (Picea abies, Populus alba, P. tremula, Salix alba) suitable for long-eared owl individuals. In Bacau city a small colony of 7 individuals was located in the yard of the Astronomical Observatory, with several trees of Thuja orientalis, Picea abies, Carpinus betulus. Both locations are situated within the cities limits in heavily urbanized areas.
In Chisinau 599 pellets have been collected and in Bacau 82 pellets. Each pellet was measured, weighed and afterwards unfolded. The bone fragments were cleaned and sorted into categories. Small mammal species were determined accor-ding to cranial bones and dentition (34,35). The sibling species Microtus arvalis and M. rossiaemeridionalis, Mus musculus and M. spicilegus that can't be differentiated morphologically were considered as genus Microtus and Mus, respe-ctively.
The ecological analysis of the prey species was performed using the indexes of abundance (A=no*100/N, where no -number of individuals of a species, N -total number of individuals); frequency (F=nop*100/N, where nop -number of pellets with certain species, N -number of pellets); total biomass of consumed prey (B=no*G, where no -number of individuals of a species, Gmean weight of one individual). The mean weight of prey individual was calculated from our own data gathered during long term studies of small mammals and bats. The trophic niche width was estimated using the B Levins' index: B=1/Σp 2 , (36), in its standardized version Bs (37): Bs=(B-1)/(n-1), where p is the fraction of items in the diet, and n is the number of possible food categories (38). Bs ranges from 0 (100% utilization of a single food category) to 1 (equal use of all categories).
During the study none of animals was injured or sacrificed.

RESULTS
In Chisinau the length of analyzed pellets varied from 1.16 to 6.95 cm with the average of 3.32 cm. The pellet weight varied between 1.2 and 6.07 g with the average of 2.52 g. After cleaning the bones, 1489 individuals were identified. The number of individuals per pellet varied from 1 to 6, the average constituted 2.46 individuals. In Bacau the pellet length varied between 1.2 and 5.6 cm. The minimal number of individuals/pellets was 1, the maximal number was 5 and the average was 2.56. After cleaning the bones 223 individuals were identified.
The trophic spectrum of long-eared owl in Chi-sinau consisted of mammals from 3 orders (Sorico-morpha, Rodentia, Chiroptera) and passe-rine birds ( fig. 1). In Bacau rodents and passerine birds have been identified ( fig. 2). In both sites Microtus species dominated with 70.99% in Chi-sinau and 76.31% in Bacau. The house mouse is the second species in Chisinau pellets (10.88%), while in Bacau it constituted less than 1%. The genus Apodemus were represented by 4 species in Chisinau and by 3 species in Bacau. In both sites the most numerous was A. sylvaticus with 10.34% and 10.97%, respectively ( fig. 1, fig. 2). Other Apodemus species constituted about 10% in Bacau pellets, while in Chisinau their ratio was less than 4%. In Chisinau the diet of long-eared owl was more diverse, probably due to much larger number of individuals that hunted in a larger variety of ecosystems. Here were identified shrews and bats in lower ratio, while the birds constituted 2.55% and in Bacau -2.19%. Among rodents two more species have been registered -the arboreal rodent Muscardinus avellanarius and the synanthropic species Rattus norvegicus with very low ratio of 0.13%.
The diversity indexes (Shannon and Simpson) are higher in Chisinau site 0.45 and 1.89, respectively, than in Bacau 0.71 and 1.68. Although the species number is much higher in Chisinau, the difference between diversity indexes is not very high, due to more even distribution of the species in Bacau site. The highest frequency in pellets from both urban areas belongs to Microtus species that was found in most of the pellets followed by Mus species and A. sylvaticus in Chisinau and by A. sylvaticus and A. flavicollis in Bacau (tab. 1). The birds, represented by Passeriformes had a frequency of 6.43% in Chisinau and 6.1% in Bacau.
The total biomass of prey items constituted 43 953 g in 6 study months in Chisinau and 7 038 in 4 months in Bacau. The highest biomass belongs to Microtus species, with 31 710 g in Chisinau and 5 220 in Bacau (tab. 2). In both sites a decrease of prey number and biomass was registered from November to December and from November to February in Chisinau.  The trophic niche index in Chisinau site was 1.89 and varied monthly between 1.58 to 3.77. The standardized index was of 0.089 and varied monthly from 0.058 to 0.28 and indicate that in December 2012 the prey used belonged to many categories with more even distribution. In Bacau the trophic niche index was 1.67 with low variation degree between months. The standardized index was of 0.134 and varied slightly among the studied months (tab. 2). In Bacau WTNs index was slightly higher because only prey categories hunted there were considered.
The difference between the ratio of Mus species in both cities is very high. This fact can be explained by city size and structure. In Chisinau there are many tall buildings and a massive production of waste, while in Bacau small houses are most numerous and the city is much cleaner. The higher ratio of Mus species (up to 10%) in winter diet of the long-eared owl was noted for large cities (9,21,29,40,45) and much lower ratio, up to 3% in small cities (17,24,43).
Among other rodent species in Chisinau pellets there were found R. norvegicus and M. avella-na-rius. The last one is arboreal species and usually hibernates during winter, therefore its share is very low in different regions of Europe, up to 1% (21,28), but in most of studies it wasn't re-gistered. The brown rat had a very low ratio in Chisinau pellets and wasn't registered in Bacau, although in previous studies it was found in A. otus diet with 0.14% (23). In many other studies in European cities the species also had a low share, up to 5% (9,20,21,29,31,39), but in some large cities the species is one of the main preys, reaching about 20% and 60-70% biomass (28).   (46). The presence of bats in the diet of A. otus is usually accidental and constitutes less than 0.5%, while in the diet of other owl species (Tyto alba, Bubo bubo) Chiroptera groups can reach more than 10% (47,48).
The passerine birds constituted about 2-3% in A. otus diet from both cities, as well as in other urban studies, where their share constituted 0.5-10% (26,29,39,40,43,49). The higher ratio of birds in some studies is conditioned by the abundant snow cover, when owls can shift their hunting areas into urban habitats, where the availability and density of bird populations, especially house sparrow, are higher (4). In the studied period in urban localities Chisinau and Bacau the snow cover did not exceed 10-20 cm and in November-December periods there was no snow cover, therefore the share of birds was rather low.
The prey diversity is higher in Chisinau site than in Bacau, which is due to larger surface of Chi-sinau city and to larger number of long-eared owl individuals. The higher diversity in larger cities was mentioned in many other studied (21,28,29,40), while in smaller localities the diversity is lower (22,26,39).
The long-eared owl is a specialized predator and hunt individuals that weight between 15 g and 50 g, therefore, the ratio of preferred prey -Microtus voles remain high in spite of the availability of other prey types (1,2). According to optimal foraging theory only the abundance of preferred prey influence upon the optimal choice of prey type, while the abundance of other prey types is not important (50). The close values of trophic niche breadth in Chisinau and Bacau prove the high hunting specialization of the long-eared owl and highlight its importance in rodent regulation in urban areas and surroundings.

CONCLUSIONS
1. The trophic spectrum of long-eared owl in Chisinau and Bacau cities consists of mammals and birds, the rodents being the dominant trophic source (8 species in Chisinau and 5 species in Bacau with over 95%). The Microtus species were the main prey and constitute more than 70% in both sites.