Branta Issues

Features of migratory movements of Black-headed Gull Chroicocephalus ridibundus through the territory of Ukraine from the central region of the European territory of Russian Federation

A. M. Poluda, A. O. Markova

The Ukrainian territory is extremely important for Black-headed Gull during the autumn migration. T. Shevareva (1965) believed that these gulls from central region of Russia’s European territory are staying for about 3 months in the area of the Middle and Lower Dnieper river, in the lower reaches of the Don river and in the Sea of Azov. She called it an intermediate mirgation. According to O. D. Popova-Bondarenko (1987), some individuals reach the mouths of the Dnieper, Dniester and Danube, moving in a south-westerly direction. That is, during August-October and even in November they are mainly on the Ukrainian territory and practically do not migrate. The aim of this article is to establish whether birds of this species really have an intermediate passage and to determine the timeframes of the migration from the central region of Russia’s European territory through Ukraine.
The article contains the results of the analysis of all direct recoveries of young Black-headed Gulls (birds of the first year of life), which were ringed in 1927-1940 on the lake Kyiovo (Moscow region, 256 findings), in 1957-1959 in the Horkivskyi Reservoir (Nizhnii Novgorod region, 204 findings) and in the Riazan region (65 findings).
Several processing programs were used to analyse Black-headed Gulls ringing data (recoveries) and, first of all, to determine the level of their migratory activity. Particularly, the GIS package «ArcView GIS 3.1» was used to calculate the distances between ringing sites and bird findings, azimuths between them. The same program was used to map these points. Oriana v.4.0  software was used to analyze ringing data for statistical calculations of bird movements: mean movement vector (μ), standard error of the mean vector (m), the length of the mean vector (r), 95% confidence interval of the mean vector, level of significance (p) according to the Rayleigh test. The nonparametric Mardia-Watson-Wheeler test (MWW) test (Batschelet, 1981) was used to compare the mean vectors of the two groups of birds. To determine the degree of similarity of the two samples of the spatial distribution of the findings the Mardia test was used, the calculation program of which was written by J.Hines (Hines) and adapted by S.P.Kharitonov (1997). To visualize the data on the spatial distribution of the findings of ringed young gulls the method of Kernel density estimation in the program Quantum GIS 3.10.10 was used. The result of this is the creation of a density raster (heat maps) of the points of the input vector layer per unit area. Kernel density estimation of registration points and construction of heat maps was performed separately for each month, combining data from three breeding groups.
To find out the features of migratory movements of young gulls of each of the three breedings groups, the monthly spatial distribution of the sites of findings (recoveries) of ringed birds was analyzed. The analysis began from July, the first full month after the end of the nesting period of the vast majority of Black-headed Gulls, and ended with the findings of ringed birds during the winter, that is during December-February. To understand the level of migratory activity of these gulls during a particular month, several indicators were analysed and compared with those from the previous or next month. The degree the reliability of the differences, if any, was statistically checked. In particular, calculations of the average movement distance, the average movement vector and the mean coordinate points of all found birds were made, and the distance and azimuth of the movement relative to the parent colony were calculated for each recovery.
The general patterns in the monthly distribution of ringed Black-headed Gulls have been identified. It is the analysis of the spatial distribution that makes it possible to estimate the level of migratory activity (intensity of migratory movements) in a given period of time. The average coordinate points for each month (and the winter period, which covers 3 months) for separate breeding groups were calculated. The presentation of this information on the maps clearly shows that the real migratory movements of Black-headed Gulls from all colonies begin already in July - the average coordinates point of the bird findings from the lake Kyiovo was in the Sumy region at a distance of almost 600 km from the colony. The similar points of bird findings from Nizhnii Novgorod and Riazan colonies are more than 2 times closer to the places of their birth (290.4 and 224.3 km, respectively). In August, gulls from the Kyiovo colony virtually stop their migratory activity (the displacement of the average coordinate point during this month is only 78.4 km), whereas birds from the other two nesting groups increase their migratory activity (average coordinates points moved by about 470 km). In general, during July and August, most of the Black-headed Gulls from the Horkivskyi Reservoir and the Riazan region make large-scale movements – the average coordinates points for these two months are moved by 760.3 km (for the first region) and 694 km (for the second). In September, these birds slow down their migratory activity (the average coordinates points of Nizhnii Novgorod gulls moved only by 37.6 km, and Riazan gulls – 111 km). While the Kyiovo gulls, on the contrary, increase the activity – moving the point by 306 km. During October, the activity of migratory movements of birds from the Kyiovo colony is at a low level (the average coordinates point moved by 135.3 km in the direction perpendicular to the general one – to the northwest). At the same time, gulls from the Horkivskyi Reservoir and the Riazan region increase the scale of migratory movements. And already during November and, especially, December birds of all three groups make the most large-scale movements – moving the average coordinates points during the last month by 403.6 km (birds from a colony on lake Kyiovo), 701.9 km (Riazan gulls), 861 km (Nizhnii Novgorod birds).
It was important to find out how the results of our analysis are consistent with the conclusions of previous researchers (Shevareva, 1965; Popova-Bondarenko, 1987). They claimed that the Black-headed Gulls from the Central European region of Russia, having reached the territory of Ukraine in early August, practically stopped migratory activity for about three or four months (August-November). According to our data, the picture of migratory movements of «Kyiovo» birds, which gave ringing recoveries in 1927-1940, is a little different. In particular, they migrated according to this scheme – during July, September, November and December birds made significant migratory movements, and in August and October, they virtually stopped migratory activity. Gulls from the Nizhnii Novgorod and Riazan regions migrate, as mentioned above, in this manner – most birds actively move in July-August and October-November-December, and in September their migratory activity is minimal. All these periods of decrease  or suspension of migratory activity of birds of three breeding groups really occur in the months when most of them were in Ukraine – one month for «Riazan» and «Nizhnii Novgorod», two – for gulls from lake Kyiovo. 
Vector analysis of directions (Mardiae-Watsone-Wheeler test) and analysis of the spatial distribution of the ringed bird findings (Mardia test) showed that the migratory characteristics of Black-headed Gulls from the lake Kyiovo colony is significantly different from birds from the Riazan region, and especially different from Nizhnii Novgorod gulls. Most birds from these two regions make autumn movements in one corridor. «Kyiovo» birds migrate adhering to more southern directions (μ=201.9±1.6°), in comparison with «Nizhnii Novgorod» (μ=206.5±2.4°) and, especially, with Ryazan birds (μ=212.9±3.4°). The average coordinates points of all recoveries of ringed Black-headed Gulls from three regions are located on the territory of Ukraine, in particular, from the Horkivskyi Reservoir – in the Kharkiv region (50°10´N 36°22´E), from the Kyiovo colony (Moscow region) – in the Kirovograd region (48°29´N 32° 26´E), from the Riazan region – in the Dnipropetrovsk region (47°53´N 34°06´E).
There are also differences in the time that Black-headed Gulls stay in the areas of their native colonies in different regions (up to 100 km) – birds from the Moscow and Riazan regions practically leave them until September. Whereas a significant proportion of individuals from the Horkivskyi Reservoir were in this area during September (13 findings – 6.4% of all recoveries) and October (8 findings – 3.9%).
The territory of Ukraine is extremely important for Black-headed Gulls from the central part of the European territory of Russia. Most of the recoveries of ringed birds from the three regions, which we analyzed, belong to the territory of our country – in particular, these fractions of all findings of Riazan gulls is 72.3%, Moscow – 59.4%, Nizhnii Novgorod – 52.0%. But, it is clear that these percentages are even higher during migration. For example, during August-November, they accounted for the first 80% (44 findings of all 55 in this period), for the second group – 70.5% (total number of recoveries is 193), and for the third – 57.7% (175 findings). All this indicates that the migration routes of the vast majority of these gulls pass through the territory of Ukraine and, it is clear that the closer the colony, the higher the percentage: the gradation is as follows – the colonies in the Riazan region located at a distance of about 500 km from the border, Kyiovo colony - 550 km, and Nizhnii Novgorod colony – more than 700 km. Some birds from the last colony migrate east of Ukraine – through the Rostov region and even through Volgograd and Astrakhan regions.