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Variety of Long-Eared Owls (Asio otus L.) Diet as Index of Habitats Usefulness.
Alexander S. Gatilov, Vladimir I. Voronetsky Department of Vertebrate Zoology, Faculty of Biology, Lomonosov Moscow State University, Leninskie gory, 1, k.12, Moscow 119992, Russia e-mail: gotya@pisem.net, gotya@nm.ru
Bank vole skeletone (prey of long-eared owls)
Introduction As the theoretical base of ecology researches practically any species of vertebrate animals serves population biology because population is the basic structural unit of a biodiversity and a point of evolutionary forces application. Any population, by definition of known Russian zoologist N.P.Naumov (1977), only « the part of a complete species connected statistical-probability by connections with other its same parts for multilateral information interchange and joint actions during existence of a species in the concrete environment ». Having studied ecological, genetic and other features of a population, it is possible to reveal the factors determining prospect of prosperity or decline of a species in changing conditions. In modern conditions, populationary-ecological researches get special value in connection with the decision of problems of rational use and protection of alive biosphere resources, for an estimation of pollution and infringement of the natural environment, and as for an estimation of the economic damage rendered by such influences. In conditions of system crisis experienced by our society the urgency of the named problems not only is kept, but also amplifies, in view of easing control function of the state concerning observance of the nature protection legislation and display of injurious exploitation of natural resources. Anthropogenous pressure upon natural populations today accompanied by reduction intrapopulationary polymorphism and increase inadaptive spatial differentiation that already has led to excess of allowable genetic changes and already it inevitably predetermines the further degradation of biosphere (Altukhov, 1995). Globally aggravated by the end of 20 centuries problem of natural environment transformation should lead a human society to understanding necessity of preservation specific animals' variety. The majority species of predators - consuments supreme orders, finishing trophic circuits in ground ecosystems, are today in rather disturbing position. Destiny many of them in conditions transforming habitats appeared in a doubt. Owls - original group of predatory birds adapted to active existence in conditions of limited visibility. As well as any other predators, they are the integral element natural biocenosises. The economic activities of humans directed on constantly growing use of natural resources, result in gross infringements of functioning ground ecosystems, that in the determining image affect and a condition of animal communities, and on a condition of consument's supreme order population. Recently scientific and public interest to this group of birds has considerably raises (and it is connected not only to an output of books Joanna Roling). This interest is supported today not only a weak level of scrutiny of the given group (practically annually in tropics continue to describe new species). Owls draw to themselves attention, due to a number of such features, as a wide circulation practically in all natural zones, an originality of ecology, behavior and morpho-physiology; prospect synantropisation some species on a background of disturbing decrease in number of others, difficultly observable and, still, poorly studied. Practically in all territory of Europe today it is impossible to find a territory, where global influence of humans' activity would not affect. Many kinds of predatory birds are not casual appeared under threat of disappearance, and in their attitude, various
forests and hummocky-sedgy black alders forests. sphagnous-sedgy bogs covered with Archangel pine. As the most part of a forest cover was exposed to repeated influences - cabin, ploughing up, to fires, - the area of original primary forests is rather insignificant, and the most part forest-covered is submitted to territory secondary forests from smallleaved trees - birches and aspens. Around of villages and settlements, locate the fields sowed forage crops (motley grass or maize, etc.). Some fields did not swing open already long time and have turned in motley grass meadows used for preparation of hay and pasture of cattle. In parallel researches were carried out in territory of Moscow-city, in various parks and forest parks (Cuscovo, Park « 50 Years Of October », Kuntsevskiy park, the Botanical Garden of the Moscow State University, etc.). Annually in spring, these territories surveyed with the help of the pedestrian routes; in parallel were carrying out interrogation of local population (especially in territory of Moscow) with the purpose of detection maximal number of nesting pairs. As far as possible, about each nest, and also under male perches, gathering pellets and record quantity of eggs and fledglings in each nest was registered. In addition, we descript nested and adjoining biotopes. In vicinities of the Biological research station in different years nested up to 15 pairs long-eared owls (Asio otus otus Linnaeus, 1758). For nesting, as well as the preference is peculiar to this species given small groups of coniferous trees (mainly to fir - -58 %, less often pines-20 %), were less often used deciduous trees (from them most frequently willows of-8 %). However, it is connected to a nesting stereotype of Corvidae, which nests are used by the long-eared owl (most constructions hooded crow 88.5 %, less often magpie-9.5 % or other bird (for example, the hawk) are frequently used). The preference given forest biotopes, located near to preferred hunting places different meadows, pastures or other open spaces. It is connect to evolutionary fitness of the long-eared owl to hunting on popular small mammal, basically from a wing (up to 90 % of all hunting time). Thus, the greatest preference given various combinations of meadows and tillages-72 percent, other types agricultural places and sites of recreational zones are less often used.

3.Among victims of long-eared owls borrow a similar place other species of voles (root vole M. oeconomus, field vole M. agrestis and bank vole Clethrionomys glareolus), in total components of 2-15 %. However their occurrence in gathering depends as well on type of biotope in which most the owl frequently hunts: M. oeconomus gravitates to more damp biotopes, and, hence will be more often to meet at hunting on valley meadows, M. agrestis - on arable lands, Clethrionomys glareolus - at hunting in forest biotopes. 4.Considerably the smaller share in usual conditions is made by shrews (Sorex araneus and S. minutus), besides, their power contribution is insignificant because of small sizes: the weight of one shrew makes 3-15 g while the weight of one vole can reach 50. 5.Such synanthropic species as a grey rat (Rattus norvegicus) and house mouse (Mus musculus), can make a significant share (up to 30 %) in a diet long-eared owls living near to large populations of these rodents (for example, near to a farm or an battery farm) and having an opportunity on them hunts. 6.Birds become extraction long-eared owls rather seldom (as against tawny owl, for example) as it specializes on fine mouse-likes rodents; however, despite of it, at an opportunity rather easily extracts their owl can even overspecialized on them and even to bring up them posterity. 7.Other animals meet in gathering in individual number, that is caused by their low number in the given place (water vole Arvicola terrestris, bush mouse Sicista betulina etc.), and sometimes, also seasonal occurrence (cockchafers - Melolontha hippocastani and bats - Chiroptera). Hit their remains in a pellet appreciably the casual phenomenon. 8.The number of pairs wich started Long-termed dynamics of voles and owls nestingin this season, 2500 45 size of an egg-laying, 40 and is especial, number Number of 2000 35 fledglings depend on fledglings quantity of basic of a 30 1500 species - victim (M. 25 Number arvalis) of hatchs with rare 20 exception (if the owl has 1000 15 an alternative feed Number source a large 10 500 of hole/ha population of mice or, 5 even, sparrows on a 0 0 farm or a granary in the neighborhood it Years practically does not depend from voles and it can successfully breed even within low number of voles). 9.Under adverse conditions (bad weather a significant part of time or simply year of voles number depression) the spectrum of owls feed changes: the share common voles (sometimes rather considerably) falls and shares of minor, additional power supplies - mice, shrew, birds and insects grow. Shannon-Winner's index thus grows
Numbers of fledglings/hatchs
1 1 9 3 5 1977 9 3 5 1987 9 1 3 196 197 197 198 199 197 197 198 199 199 198 198 5

measures on maintenance and protection of specific populations are undertaken. Programs on breeding in captivity and to the subsequent release on will of many kinds of owls (an eagle owl - Bubo bubo, barn owl - Tyto alba, pygmy - Glaucidium passerinum, Tengmalm`s - Aegolius funereus and little- Athene noctua owls) have been developed and realized. Methods of repatriation in the West-European countries Ural Strix uralensis and great grey owl - S. nebulosa, a marsh owl - Asio flammeus were developed. Ground Russian biocenosis during all 20 centuries, and it is especial in its second half, were expose to so scale transformation, as well as the natural environment of industrially advanced countries of the West. The European part of Russia officially recognized as a zone of the sharpest ecological situation (« the National report of Russia on a condition of an environment », 1992). And, though in comparison with practically completely changed landscapes of the Western Europe, the natural environment of Russia has suffered that human's transforming activity be relative less, significant decrease in number of specific populations and degradation of their structure at many diurnal predators and owls recently is here again marked. Transformation of landscapes by cutting down native forests, scale land improvement of bogs and fluvial plains, recreational press, environmental contaminations by fertilizers, pesticides, insecticides and waste products, creation extensive man-caused, recreational zones and a "cultural" landscape - all this, finally, to a greater or lesser extent changes the environment of existence of many kinds and predetermines reciprocal change of norm of reaction on the part of their populations. In conditions of so significant change of natural environment, and as direct prosecution by humans (within several decades in USSR territory there is official company on « to struggle against predators in the nature »), many species of owls was carried out, as well as diurnal predatory birds, show last decades appreciable decrease in number both specific, and some local populations - the barn owl, an eagle owl, a marsh owl, little and Tengmalm`s owls, scops owl. The long-eared owl (Asio otus L.) - widely widespread and characteristic representative of ordo Strigiformes. This kind characterized by a set of such biological features, which allow counting this predator a good modeling kind for populationaryecological researches. At the golarctic distribution, it occupies an extensive area with a various environment. Surprising genetic uniformity of this species shown in the minimal number of geographical forms in boundaries more than an extensive area. Thus, the genetic material on a regular basis mixes up due to a distant dispersion of a significant population part. It is essential, that such genetic features are combined with narrow food specialization on voles, with use of the changed landscapes for reproduction and wintering and some other, testifying about significant tolerance of the long-eared owl to the Anthropogenous factor. Thus, in various conditions of existence the long-eared owls, apparently, realizes the, species-specific norm of reaction to parameters of an inhabitancy and on their change. It is obvious, that in these conditions it is necessary to count actual studying of key parameters of a specific population and its regulating mechanisms in conditions of amplifying Anthropogenous influence. Place of research Ecological features of any species are to some extent predetermined by the natural environment which provides conditions of existence both species, and community of animals, its associates. These researches were carrying out in territory Zvenigorod's Biological research Station of the Moscow State University located in Odintsovskiy district of the Moscow's area nearby to Zvenigorod (in 50 kilometers to the West from Moscow). The natural environment of this area represents a typical Anthropogenous landscape of the Central region of Russia. The kept sites natural biotopes here alternate with different types of the changed landscapes and with humans' artificial constructions. All named space is characterized by a complex and rough relief as settles down at a joint of three large physico-geographical areas of Moscow suburbs, at outskirts of the extensive Smolensko-Moscow height past the long and complex period of geological formation. The territory on which carried out research, is at a southern limit of a taiga zone, on a joint of two biogeographically subzones: conifero-deciduous (mixed) and deciduous forests. Native forests of mixed forests subzone are formed basically by a spruce fir, an English oak and a smallleaved linden. Secondary forest species are an elm, a bird cherry, a black alder, a birch, a Norway maple and an aspen. Modern distribution of vegetation to territories of our researches has developed under action of complex system of factors - geomorphologic, climatic, and during historical time anthropogenous. Forest communities generated depending on features of the relief connected to it of humidifying and a microclimate. On northern slopes starved hills, on poor overwetting soils and on thin integumentary loams, there are sites of typical fir-tree southern taiga forests. On the slopes of a southern exposition that well warmed up and with richer sod-podsolic soils, there are oak and lime groves. On slopes of ancient river terraces and on water-separate eminences with sandy soils are distributed only pine and pinedeciduous forests. Along with the mixed forests, in vicinities ZBS the Moscow State University is widely Here, on these pines there is a nest of distributed bogs; the most part low- long-eared owls. They used it almost every year. lying and riding bogs afforestate birch

Materials and methods Like many other birds (according to a survey by the International Bird Pellet Study Group in 1969, 330 species of over 60 families produce pellets: f or example robin (Erithaceus rubecula), starling (Sturnus vulgaris), tree sparrow (Passer montanus) and heron (Ardea cinerea), owls produce pellets too. But its pellets have Pellets of long-eared owls, gathered under the nest some specific characters: because of rather low acidity of gastric juice bone components of victims have the best safety, also to this promotes encouragement owls to swallow a victim entirely, not crushing. On the other hand the pressure developed by walls of an owl's stomach, reaches 20 atmospheres. In result the most part of not digested rests developed into characteristic oblong clod on the average in the size 32*19*16 mm and weight 1.56 g (from 12*9*5 mm and 0.1 g and up to 68*35*35 and 6 g). Further pellets were expose to analysis separately (well kept) or in a lump. For this purpose pellets soaked in hot water approximately for day. Then the received "mass" repeatedly washed out and, in result, large bone remains settled on a bottom of capacity and selected for definition, small bones caught with the help of a tweezers. Also, during washing from hair weight the rests of chitinous armour of the eaten insects got out. Small samples of the undamaged pellets, and also pellets containing plenty of insects' remains understood dry, with the help prepared needles and a tweezers. Usually bone fragments make a small share of weight pellets - on the average 24.9 % (from 1.7 % up to 41.7 %,), however they rather authentically reflect a diet long-eared owl. Average pellet contain about one Contains of these pellets: sculls, jaws, pelvises and and a half skulls and three jaws (about four other small bones.
skulls and seven jaws are maximum), however, occasionally, it can consist only of wool and the very small bones which are not subject to definition. Further, the selected material dried up and cleared with the help of a rigid brush, and then determined with the greatest possible accuracy. Definition was conducted basically to cranial attributes (in particular on a teeth), other bone material was used for the control of number of individuals (the number pelvic bones of rodents could appear more numbers of skulls or pairs jaws, for example in case of analysis nestlings pellets, as parents frequently tear off a head to a victim before giving its nestling; in such rare cases the part of individuals cannot be with confidence identified up to a species), the number of skulls and pairs jaws is usual rather considerably exceeded number of anyone postcranial parts of a skeleton. Thus, skulls possessed the best safety, despite of rather strong influence of digestive system (usually damaged only the brain capsule which is hasn't important regular attributes; less often the skull broke up to two half or lost a forward part with cutters, however, even, despite of all this the basic regularly important attributes nevertheless were usually kept). For all received gathering, it was calculated Shannon-Winner's index on following formula: H= (pi ln(pi)) where pi - a share of this species in gathering. Results With the help of this index we can estimate a variety of feed spectrum: than a feed, the below in it a share of the basic victim is more various, the index is higher (an index can be from zero and is higher, however it seldom happens more than 1.7). And, though it also does not reflect all structure of victims' spectrum (for example, at use as the basic food resource a species replacing it, the index can be small, however it does not reflect overspecialization on other food object). This year have been found two pellets, containing on 14 Nontypical pellet, founded remains cockchafer and about dozen various fine bugs this summer contained and only by one common vole (some teeth from the different parts of beetles (cockchafer) - heads, jaw). From the collected material (there are data since legs, wings and wing 1982 inclusive), it is possible to reveal the following cases and little amount of voles wool. rules: 1.The basic object on which in our district specialize long-eared owls is common vole (Microtus arvalis), usually it makes 60-98%, but sometimes, for example, in one year of peak of number common voles, pellets can consist on 100 % from its remains. 2.Other, not less important objects of a diet are Apodemus agrarius and Sylvaemus uralensis (Apodemus sylvaticus) - common and striped field mice; their percentage in pellets in the similar image depends on type used hunting biotope.

Adult owl brings young sparrow from birddealer to his fledgling. Photos by Voronetskiy V. I.

(though and not always - for example, in the mentioned above case with cockchafers, H=0.92). The number owlets on a nest is in that case authentic less This winter because of early struck strong frosts the population of the ordinary vole has strongly decreased (for all summer in traps has not got any grey vole - only to the mouse and bank voles). Therefore this year long-eared owls in vicinities of a biological research station were not reproduces, all started egg-laying have been throwned (including in places of annual nesting). Thus in 80 % their diet began P a ss er sp . to make a 60 % R a ttu s no r ve g ic us significant part Ap o d e m u s &S ylva e m u s (up to third) 40 % shrew (Sorex S ylvae mu s u rale n s is 20 % sp.), shares of Ap o d e m u s a g ra riu s mice 0% (Apodemus&Syl Microtu s s p . vaemus), and Microtu s arv a lis birds have strongly Microtu s ag r e s tis P lac e , ye ar , s e a s o n increased. During mass summer flying of the cockchafer, it on a regular basis met in owl's pellets. 10.During wintering a S h are s o f p re y s i n "ru ral " o w l p e l l e t Ave s variety of 10 0% extraction too So r e x m in u tu s 90 % 80 % grows, especially So r e x a ra n e u s 70 % the share of birds 60 % Oth e r ro d e n t s (sometimes they 50 % are absent in A p ode mu s &S y lvae mu s 40 % spring and 30 % C leth rio n o m y s g la reo lu s 20 % summer gathering 10 % and appear only in Microtu s s p . 0% the middle of Microtu s oe co n o mu s winter) frequently Microtu s arva lis increases 11.The Microtu s ag re s tis P la c e, year, s e as o n structure of victims of "city" and "rural" owls stably differs: the food "city" owls as a whole is more various (and, hence Shannon-Winner's index stably is higher), in their diet of a bird meet all-the-yearround and take more significant place, than at "rural" owls. Above a share of representative's Muridae family, it is especial synanthropic species. Thus, a variety of a diet of the long-eared owl, appreciated with the help of various methods (for example with help Shannon-Winner's index) allows estimating comfort of dwelling in the given place and at present from the point of view of the long-eared owl. However thus it is necessary to take into account the various features of each habitat especially well appreciable at long-term monitoring.
Ave s

S h a re o f p re y s in o w l p e lle t s in Mo s c o w

10 0%

Pa ru s sp .

MSU 1988 spring

BotGarden 1989 winter

Kuntsevo 1985 winter

BotGarden 1989 summer

BotGarden 2003 winter

"Mirniy" 1989 su

"Yolochka" 1999 su

Lutsino 1986 su

Lutsino 1989 su

Lutsino 2003 sp

Numbers of hole/ha