INFLUENCE OF ANTHROPOGENIC FACTORS ON THE ECOLOGY OF MELANOCORYPHA CALANDRA AND ALAUDA ARVENSIS IN DEPRESSIONS OF DNIPRO — MOLOCHNA

Regional studies, The research was carried out for 3 years in the steppe biotopes of the bottoms of the Ahaymany, Barnashivsky, Green, Big Chapelsk, and Small Chapelsk depressions of the Dnipro — Molochna interfluve. Based on visual inspection and processing of space images, the degree of anthropogenic transformation of these ecosystems is analyzed. The highest percentage of plowing is characteristic of the Ahaymany depression, which occurred in the last 10 years. Among the factors that significantly affect the nesting birds of the steppe complex are also the continuous low mowing of grass (Green depression) and overgrazing of livestock — Small Chapelsk depression. The nesting density of background steppe species was determined, the highest density of Alauda arvensis in different years is characteristic of Ahaymany (245,2 pairs/km 2 ) and Barnashivsky depression (211,2 pairs/km 2 ), and Melanocorypha calandra — for the Big Chapelsk depression (140,1 pairs/km 2 ). Stable is only the territory of the Big Chapelsk depression the protected regime under moderate grazing load of wild ungulates. A positive correlation was established between the values of steppe habitat area and Alauda arvensis nesting in the Ahaymany, Barnashivsky, Small Chapelsk, and Green depressions and, accordingly, a negative dependence for Melanocorypha calandra.


INTRODUCTION
In recent decades, the southern steppe region of Ukraine has again undergone significant changes, then the activation, then the decline of human impact on the remnants of natural ecosystems. Natural processes in the southern steppes, which have formed the modern fertility potential of the agroecosystems, are entirely disrupted. First of all, this is accompanied by the loss of quantitative and qualitative characteristics of species biodiversity, which has shaped the mechanisms of sustainable functioning over the centuries. For species diversity that is not used by humans, leaving only those areas that its characteristics are unsuitable for intensive agricultural production. One of such territories is depressions in the interfluve of the Dnipro -Molochna. And its largest depression ecosystems are included in the objects of the Emerald Network [1][2][3][4].
At the same time, these remnants of natural ecosystems are significantly affected by exogenous and endogenous processes, most of which are again associated with human activities. In particular, complete plowing of catchment basins, over-regulation of beams that filled the bottoms of depressions, mowing of natural gras-ses, unbalanced grazing of ungulates, mowing of grasses, and in protected areas -a kind of reserve succession [5; 6]. Each of these factors has a mainly negative impact on ornithocomplexes, which can be traced in the number of species, density, and biomass.
The aim of the work is to establish changes in the ecology of two background steppe bird species in the depression ecosystems of the Dnipro -Molochna interfluve under the influence of anthropogenic transformation.

ANALYSIS OF THE LAST RESEARCH
AND PUBLICATIONS Birds of steppe and agro landscapes in the interfluve of the Dnipro -Molochna have repeatedly attracted the attention of researchers. The systematic composition of the avifauna is well studied. Relatively complete data on the ecology of species, their distribution in protected areas [7], agro landscapes have been published [8; 9], and the authentic steppe [10; 11]. Regional studies, mostly performed by scientists of the Azov-Black Sea Ornithological Station, Askania-Nova Biosphere Reserve, Melitopol State Pedagogical University, give a generalized de-№ 2/2021 99 Збалансоване природокористування scription of the avifauna of the region [12][13][14][15], or relate to individual depressive ecosystems, such as the Big Chapelsk depression [16][17][18], or individual species [19][20][21]. However, despite the study of birds in the region, under the influence of anthropogenic factors, there is an acceleration of changes in their ecology, which should track, analyze and take action to minimize the negative factors.

MATERIALS AND RESEARCH METHODS
To assess the state of ecotopes, their changes under the anthropogenic influence, materials obtained as a result of ground-based visual inspection and analysis of space images of the Sentinel-2 region were used. Studies of the population structure and lark numbers were conducted during 2018-2020 in the depression ecosystems of the Dnipro -Molochna interfluve. For this purpose, laid accounting transect with an area of 0.14 to 0.33 km 2 were established. The area of the model plots was 2.14 km 2 . During the research period, we covered 63 km of walking accounting routes with different modes of nature use. The density of singing males, and behind them the estimated number of nesting pairs were determined using the route method with a fixed width of the accounting strip [22] -100 m (50 m on both sides). The routes were located closer to the middle of the studied biotopes in order to exclude ecotone effects. Birds were recorded during the nesting period in the morning and before sunset (April to June). The analysis included observations of two background species of larks: Melanocorypha calandra Linnaeus, 1766, and Alauda arvensis Linnaeus, 1758. Due to the high ecological valence of species, their characteristics are suitable for comparison in biocenoses of varying degrees of disturbance. All singing males were registered, taking into account their species identity. The calculation of the density of nesting pairs was performed according to formula 1 [23]: where n -the total number of males detected on the accounting route; M -the length of the accounting route; W -the width of the accounting route.
To compare climatic indicators, the data of the meteorological station Askania-Nova were taken, which were processed by the program Microsoft Excel.

RESULTS AND DISCUSSION
Dynamics of changes in depressive ecosystems. The research was conduct in the years that have similar climatic conditions ( Fig. 1). At the beginning of the nesting period in 2018 (April), there was almost no rain (2.7 mm -9.6% of normal), which did not stimulate the active development of steppe vegetation. The beginning of the nesting period in 2019 (April) was rainy (38.9 mm -138.9% of normal). May and June were noted the somewhat average level of rainfall and amounted to 42.4 mm (111.5% of normal) and 14.1 mm (30.6% of normal). In April 2020, there was almost no rain (7.5 mm -26.7% of normal). May and June were rainier during this period amount of precipitation were 42.4 mm and 59.3 mm -111.5 and 128.9% of normal. The indicators of the average decade temperature did not differ significantly.
It should be noted that the process of plowing fallows, depressions, coastal strips, despite the numerous recommendations of nature conservationists, in recent years is gaining momentum Steppe biotope as of 2020 remained only partially at the bottom of the depressions. Thus, in the largest of the depressions -Ahaymanynatural ecosystems now occupy no more than 12.8% of the total area of the depression ( Table 1). Part of the territory of its bottom is annually mowed for haymaking. At the same time, according to our observations, at a mowing height of 11-15 cm, larks continue to hold territory, and renest, which is due to the presence of conditions for the hidden location of nests and forage base. The upland and slopes of this depression are completely plowed, farming carried out, where only single pairs of field larks are observing on nesting.
Barnashivskyy depression situated near the Biosphere Reserve «Askania Nova». Has an insignificant difference in height between the bottom and the upland of the catchment area. The slopes and half of the bottom of the depressions are plowed. Every year the area of plowed areas increases. For 2020, 27.8% of the total area is in the natural state, where hay is also harvested annually, with a height of 11-15 cm.
The Green depression also transformed. It is cut by the main and drainage channels of the Kakhovka irrigation system. In the middle of the depression, there is a large 200-hectare storage pond on the slopes and the upland plowed. Steppe biotopes remained at the bottom of the depression their area during the study period continued to decrease -from 36.8 to 28%. Steppe areas are used for haymaking. In contrast to the above-mention depressions, mowing with grass (3-5 cm) is very noticeable here, which causes mechanical damage to the nests and leaves almost no block forest planting for re-nesting.
Small Chapelsk depression is subject to extensive economic use by grazing livestock, due to which in its south-eastern part there is overgrazing. A small part of the territory is not mowed every year, damaging the nests of birds. Unlike previous depressions, steppe areas are reduced due to littering with waste from livestock farms -6% of the total area.
The area and load of steppe biotopes of the Big Chapelsk depression, which is a part of the protected area of the Askania-Nova Biosphere Reserve, is stable. At the same time, a significant number of wild ungulates, which devour the green mass and cause its regrowth, and the real protected regime create stable conditions for the stay of birds of different ecological groups, including larks.
Dynamics of nesting density of larks. A comparative analysis of the results of bird counts in Big Chapelsk, Ahaymany, Barnashivskyi, Green, and Small Chapelsk depressions revealed a significant difference in the density of nesting pairs of Alauda arvensis and Melanocorypha calandra. Thus, the highest density of Alauda arvensis in general in different years is characteristic of the Ahaymany (245.2 pairs/km 2 ) and Barnashivskyi depression (211.2 pairs/km 2 ), the lowest -of the Big Chapelsk depression (50.1 pairs/km 2 ), and the Small Chapelsk depression (60.0 pairs /km 2 ). At the same time, the highest density of Melanocorypha calandra (140.1 pairs/km 2 ) is observed in Big Chapelsk, and the lowest density is typical for the Green depression -13.9 pairs/km 2 ( Table 2). Estimation of dynamics for a short period of research is conditional, but even during this time, the general tendency of change of density of nesting of species is already traced.

Збалансоване природокористування
In particular, for four depressions, an increase in the number of Alauda arvensis and a relatively stable density in the Big Chapelsk depression were found. Over the years of observations, the population dynamics of Melanocorypha calandra is positive only for Big Chapelsk, in other depressions the number decreases.
The impact of changes in the area of steppe biotopes areas on the number of nesting pairs of larks was determined by correlation analysis. A positive correlation has been established between the values of the steppe biotopes area and nesting Alauda arvensis in Ahaymany, Barnashivsky, Small Chapelsk, and Green depressions. And, accordingly, a negative dependence for Melanocorypha calandra ( Table 3).
The revealed dependence of the dynamics of lark density in key areas is probably explained by the biological characteristics of species as Alauda arvensis is a more ecologically plastic species it settles in semi-deserts, agro-landscapes, beams with meadow, and steppe vegetation [9; 10]. Probably, the transformation of steppe biotopes leads to the displacement of authentic steppe species of Sparrows, thus freeing up an ecological niche for Alauda arvensis.
In turn, Melanocorypha calandra is found for nesting in all areas where there are even small areas of steppe vegetation (at least 0.1 km2). At the same time, cluster groupings of a kind are trace from 3 to 5-6 pairs. But the reduction of virgin areas in both depressions ecosystems and adjacent areas leads to a sharp decrease in the number of nesting groups of this species with subsequent possible extinction.

CONCLUSIONS
Depression ecosystems of the Dnipro -Molochna interfluve, which are the most attractive biotopes for larks nesting Alauda arvensis and