The variability of territorial behavior of Sylvia warblers depending on the habitats structure of and population density

The peculiarities of territorial behavior of Sylvia warblers (blackcaps Sylvia atricapilla, garden warblers S. borin, common whitethroats S. communis, and lesser whitethroats S. curruca)were stidied in habitats with different population density. The study was conducted in the areas within the central parts of the breeding ranges of the studied species (Kaliningrad region (55°12'N, 20°50'E) and Mordovia (54°44'N, 45°30'E)) and their northern periphery (south Karelia, (60°46'N, 32°48'E), central Karelia (64°27'N, 30°17'E), and Murmansk region (67°06'N, 32°42'E)) in 2003 – 2017. The territoriality was investigated using the method of point mapping of territories as minimum convex polygons (Odum, Kuenzler, 1955). This method was partly modified in order to obtain more accurate data on sizes and configurations of territories at different stages of reproductive period. Particularly, all the observed bird's movements were registered throughout the whole period of its staying in the studied area. Also, the height at which the observed bird sang was registered to get the information about the 3D-configuration of the bird's territory. The size of a territory was assessed as the area of its projection on the ground surface. The distance between neighboring territories was defined as the minimum distance between the closest borders of these territories. The areas of territories and the distances between them were calculated using Arc View GIS 3.2 (Environmental research systems Institute, Inc. 1992 – 1999) and Google Earth Pro 7.1.8.3036 (Google, 2016, 2017). Every day we observed up to 7 birds of each species were observed. In total, every season 1 – 19 settled males and 1 – 18 unsettled males of each species. It constituted about 20 000 hours of observations in nature, more than 80 000 points marking territories mapped, and 547 nests found. Our results suggest that the territorial behaviour of Sylvia warblers has a high degree of plasticity and depends on the population density which in turn depends on the specificity of habitats. As a rule, with increasing population density the territory size (in all species except the whitethroat) and distances between neighboring territories decrease. In limited areas of preferred habitats, territorial structures became more compact and labile. When the population density was high, the majority of varieties of behavioral patterns were observed, including variants atypical for these birds. At a very high and very low population density, territoriality reduces in a similar way (shortening of the period of territory advertising with singing, decline of singing activity, decreasing of aggressiveness and territory defense degree), but for different reasons. In habitats with a low population density the reduction of territoriality apparently optimizes time and energy budgets of birds in more severe conditions of the northern regions. The reduction of territoriality and labial territorial structures under high population density provides the opportunity to participate in reproduction for a larger number of individuals. In general, the variability in territorial behavior apparently leads to the maximum realization of reproductive potential of individuals in populations under various environmental conditions. The research was conducted partially under the theme № 0221-2014-0037 "The dynamics of the fauna of birds and mammals of the Russian European North in conditions of intensive anthropogenic and climate changes: monitoring, management and conservation of biodiversity" (№ АААА-А17-117022850042-8), and partially with the support of RFBR (projects №№ 06-05-64368, 12-04-31872, and 15-05-03493).