ECOLOGICAL SEGREGATION OF THRUSHES OF GENUS TURDUS IN TERMS OF VOLYN POLISSIA

An ecological segregation of five species of thrushes (Turdus pilaris, T. merula, T. ilia cus, T. philomelos, T. viscivorus) in Volyn Polissia was studied. For the overwhel­ ming majority of ecological characteristics, the most similar are Song Thrush and Black­ bird (DE = 38.36). They have similar biotopical preferences in forest and forest edges habitats, almost the same nesting height (1.58 and 2.00 m, accordingly), similar feed rations. All this gives us the reason to conclude minimal ecological segregation of Song Thrush and Blackbird in the forest ecosystems of Volyn Polissia. At the same time, they avoid high ecological competition due to different ratios in thrushes complexes in the certain territories [22, 23], structure of nesting habitats [23]. Fieldfare often settled near open habitats by meadows and forest edges, build the nests on the prevailing tree spe­ cies within the habitat. Food preferences associated primarily with the composition of the feed, the majority of which is produced out of the forest habitats. Mistle Thrush prefers medieval pine forests without undergrowth (73 % of all habitats) with poor forest floor, that made different strategy of food use and obtaining among all presented thrushes spe­ cies. It was established that among the five studied species of thru shes Redwing and Mistle Thrush has the highest value of ecological specialization and segregation.


INTRODUCTION
In Volyn Polissia, avifauna of genus Turdus is represented by five species: Turdus pilaris (Fieldfare), T. merula (Common Blackbird), T. iliacus (Redwing), T. philomelos (Song Thrush) and T. viscivorus (Mistle Thrush). Various aspects of the biology and ecology of these species are well explored at this time. At the same time the question of environmental differences, the competitive relationship in terms of the coexistence of these species in forest ecosystems Volyn Polissia remained still open [2,28]. In addi tion, the ecological specialization and segregation of closely related species of birds, that inhabit sympatrical in particular ecosystems is still actual, what helps to understand the principles of distribution of ecological resources, development of lifestyle and the place and role of each species in the appropriate grouping [17,22].
Mentioned Turdus species shared mutual environmental resources within their nes ting range, particularly in conditions of Volyn Polissia forest ecosystems, so studying of their ecological specialization and segregation are important for the understanding of place, role and weight of each species as a structural element of a particular ecosystem. Therefore, we tried to investigate basic ecological mechanisms of thrushes coexistence and estimate the range and the character of their ecological segregation in Volyn Polissia. Research of biotopical preferences performed relatively to the breeding habitat what recorded for each founded nest. Totally 11 habitats were found (coastal scrubs, roadways shelterbelts, deciduous woodlands, mixed forests, older forest plantations, middleaged pine plantations, middleaged spruce plantations, youngaged pine planta tions, parks, orchards, black chokeberry plantations). For comparison, Thrushes trophic preferences used published data [2,5,6,11,12,19,25,26,[30][31][32].

Materials
In a field, we described the height of nest placing, measured from the ground (L), and species of tree or shrub for each found Thrushes nest.
Analysis of the results was performed with standard statistical methods. Statistical calculation was made in Microsof Office Excel 2007 and "11.0 Statistics" programs.
Biotopical distribution. Nesting of few thrushes species within the mutual habitat is normal [2,22], but the rate of each species in ornithocenozis is different.
The main priority in the selection of the nesting habitat for thrushes has the quality of feed [2,5,6]. The basis of thrushes feed compose the ground oligochaetes, whose quantity depends on moisture conditions of the biotope [5]. The trees and shrubs archi tectonic [10,11,20,27] and habitat structure (close allocation of forest edges, water or open spaces) [3,14,22] are also have an important role for nest disposition.
Cluster analysis shows (Fig. 1) [10]. Significant role for nest disposition have the deciduous tree species also. Thus, the Blackbird placed his nests on black alder in 24.3 %, Song Thrush -in 6.2 %, Fieldfarein 5.4 %. The last one build nests mainly on Populus nigra var. pyramidalis (23.3 %) and ash (10.9 %), which form monotypic roadways shelterbelts. The rate of other deciduous trees species for thrushes nest disposition is negligible. Placing nest on a particular tree species primarily depends on the nesting sites (habitats), species composition and sui table conditions for placing and disguising of nests.
As a result of cluster analysis (Fig. 2), the most similar in trees and bushes species composition for nesting are

Feeding of adults and nestlings.
On the results of the literature analysis for neighboring to Volyn Polissia areas [19,26,3032] and within the thrushes European range [2,5,12,25], the specifics of nutrition has not significant differences, however, has significant interspecific differences [2,6,24]. According to A.V. Baranovsky with col leagues [2], the character of food extraction and feature of foraging behavior formed various ecological, morphological, physiological, ethological and other adaptations which became the basis of formation of ecological differences. So, detected that highest rate of similarity is peculiar to the Song Thrush and Blackbird, the lowest -in Song Thrush and Fieldfare, an intermediate position occupies Fieldfare and Redwing, at the same time Mistle Thrush is the most remote of the four other Turdus species. The ex planation for this difference is in the variety of species feeding preferences -Redwing use larger prey then Blackbird, Song Thrush or Fieldfare; Song Thrush have the strict feeding preference of three types of prey -earthworms, caterpillars and mollusks, while the Blackbird haven't any feeding preference [11]. The last two mentioned species feeds mainly on the forest floor and on the surface of the substrate, but differs is foraging strategy [31,32]. Mistle Thrush has significant differences from others thrushes spe cies -in his diet almost no earthworms, preferred prey of medium and large size (for example, observed cases of hunting newts and lizards), most likes eat beetles, caterpil lars of owlet moth, feeds in various places mainly on a ground [25]. Despite the great similarity in feeding, trophic competition in thrushes not appear or have slight value [23]. According to A.B. Chaplygina, interspecific similarity in feeding caused by overlapping of the trophic niches [9].
In a result of cluster analysis (Fig. 3), it was revealed that most ecologically similar are Blackbird and Song Thrush (DE = 38.36). The Fieldfare is also close to them (DE = 52.92 and DE = 55.65, accordingly). From these three species considerably vary Redwing and Mistle Thrush (Fig. 3). Remarkably that Fieldfare and Mistle Thrush most differ from the Redwing with DE values 122.7 and 160.0, respectively.

CONCLUSIONS
In a result of the comparison of five studied thrushes species by major ecological performance, the following conclusions of their ecological specialization and segrega tion are formed. For the overwhelming majority of ecological characteristics the most similar Song Thrush and Blackbird (DE = 38.36). They have the similar biotopical prefe rences because prefer forest habitats and forest edges, nesting almost on the same height (1.58 and 2.00 m, accordingly) and have the similar feed rations. All this gives us the reason to conclude that ecological segregation of Song Thrush and Blackbird in the forest ecosystems of Volyn Polissia is minimal. At the same time, they avoid high eco logical competition due to different ratios in thrushes complexes in the certain areas [22,23] and structure of nesting habitats [23]. Fieldfare often settled near open habitats along the meadows and forest edges, they build the nests on the prevailing tree species within the habitat. Food preferences were associated primarily with the composition of the feed, the main part of which is obtained out of forest habitats. Mistle Thrush prefers medieval pine forest with no undergrowth (73 % of all habitats) with poor forest floor, what became the reason of feed composition and foraging strategy differences from the other thrushes species. This all leads to a conclusion that among five studied species of thrushes Redwing and Mistle Thrush has the highest value of ecological specialization and segregation.