This study presents the results of a long term study of nesting colonies of the Caspian gull (Larus cachinnans Pallas, 1811) on the islands of the Molochniy Liman and in Obitochnaya Bay (Azov Sea), in the South of Ukraine (Zaporizhia region), conducted between 1988 and 2013. A description of the size and coloring of eggs of Caspian gull was conducted by generally accepted methods. We measured 1000 eggs from 5 colonies of Caspian gulls. The background coloration of the eggs’ shells was classified into 7 types, the pattern of markings on the surface of the shells was classified into 4 types. In the nesting colonies, comprising different nesting settlements, the study tested differences in the distribution of typical and atypical coloring types and patterns on the surface of the shells. The background color and character of the shell marking patterns is dominated by eggs of phenotypes 3 and 4: gray-green, with a pattern of spots, of medium size (5–60%) and brown, with a pattern of large spots (2–40%). In different settlements the Caspian gull egg sizes vary in length and diameter of 54.5–86.3 x 39.2–60.4 mm, volume 61.7–113.7 cm3 and index of roundness 63.6–85.3%. The study revealed that the linear dimensions of eggs also depend on the number of birds in the nesting colonies. We found that morphological and dimensional characteristics of Caspian gull eggs can vary at certain intervals and characterize individual colonies, settlements and populations. Based on cluster analysis, conducted in terms of the average of the linear sizes of eggs of Caspian gull from several populations within the range of the species, the study identified three groups of colonies – Danube-Sivash, Azov-Black Sea and Caucasus-Caspian. In region of the Azov-Black Sea, the greatest similarity was shown between the settlements of Sivash and the South of Crimea, which in turn is similar to Lebiyazhyi Islands and Kaniv Nature Reserve (river Dnipro). A related link combined the Azov and Black Sea branches, while the Caucasus-Caspian group is relatively separate. As a result this study the influence of the number of nesting birds on the dimensional characteristics of the eggs was established; in the period of increase in the Caspian gull population from the 1970s to the early 1990s they had the highest scores, and in periods of decreasing population in 2001–2005, their values were lowest. Consequently, the use of oomorphological indicators turned out to be a fairly easy and objective method for studying the monitoring data for separate colonial bird species.

An approach for phytoindication assessment of the ecological factors based on diapasonal scales taking into account the cardinal points values and possible asymmetry of the plant species response was proposed. Ecological factors are modeled by phytoindicator scales with restricted range. In the central part of the factor range the species response curve has a shape that can be reliably approximated by the Gauss normal distribution. This allows completely grounded via cardinal points that are directly designated by diapasonal indicator values, calculate ecological optimum of the species. Average of species in community ecological optima scores weighted in accordance with their projective cover gives phytoindication estimation of an ecological factor. Species distribution asymmetry increases when approaching the marginal positions within gradient. This phenomenon is observed in the study of real gradients. These phenomena are also a result of the mathematical properties of ecological scales. To simulate the response of species distribution curves alternatively symmetric Gaussian model the β-function was used. This function can simulate both symmetric and asymmetric distributions. Since phytoindication performs the inverse problem in comparison with the modeling of the response curves, it is appropriate to β-function is also be used to solve phytoindication problems. Use of β-function is possible to estimate the species optimum zone based on its fundamental points with the probable distribution asymmetry of the response curve. Also, the simulation of distribution curve makes it possible to narrow the range of possible values of environmental factors, in terms of which species can exhibit the observed abundance in the community. Accordingly, this increases the informational value of species in the community and thus achieves greater reliability evaluations of the phytoindication.

Рассмотрены территориальные связи чайки-хохотуньи из гнездовых колоний, расположенных на островах Обиточного залива. Проведён анализ основных этапов годового жизненного цикла Larus cachinnans Pallas, 1811 с учётом сезонных особенностей каждой возрастной группы чаек (молодые, неполовозрелые, взрослые). На основе этих данных установлены направления и дальность разлётов, среди которых были выделены миграции: внутриконтинентальные, в пределах Украины, в пределах гнездовой области. Поселение вида на островах Обиточного залива характеризуется высокой степенью консерватизма взрослых хохотуний, широким размахом послегнездовых кочевок и дисперсией молодых птиц, обменом особями между соседними поселениями и формированием новых колоний за счёт неполовозрелых особей вида.Ключевые слова: чайка-хохотунья, кольцевание, территориальные связи, гнездовые поселения, внутриконтинентальные миграции. Considered territorial connection of Yellow-legged gull in breeding colony on islands Obitochnaya Bay. Analysis of the basic stages of the annual life cycle of Larus cachinnans Pallas, 1811 with taking into account the seasonal characteristics of each age group of seagulls (young, immature, adult). Based on this data set direction and distance of displacement, among whom were identified intra-continental migrations, domestic migrations within the territory of Ukraine and migrations within the nesting area. Settlement species on islands Obitochnaya Bay characterized by: high degree conservatism of adult Yellow-legged gull a wide range in season after nesting migrations and variance of young birds, the exchange of individuals between neighbouring settlements and the establishment of new colonies at the expense of immature individuals.