Nesting of Barnacle Goose ( Branta leucopsis ) in the Russian Part of the Gulf of Finland

. Until the end of the 1980s, the Barnacle Goose ( Branta leucopsis ) was an extremely rare migrating species in the Russian part of the Gulf of Finland, but in recent years it has become one of the mass migrants there. The first nest of a Barnacle Goose in the region was found on Dolgy Reef Island close to the Russian-Finnish border in 1995. Barnacle Geese then started expanding onto the islands in the eastern part of the Gulf of Finland. They occupied islands mostly in the northern part of the gulf, but nests were found in its central parts and close to the southwest coast as well. Barnacle Geese nested mostly on small, rocky, forest-free islands. By 2006, the size of the breeding population of this species had increased to 31 pairs. Forty nests were found in 2014, and an explosive population growth to 76 nests was observed in 2015. In 2010, Barnacle Geese started to breed on Ladoga Lake, and in 2015 the first nest was found on Onega Lake. Until 2010 Barnacle Geese had nested in the eastern part of the Gulf of Finland almost exclusively on the islands lying at a distance of 2.4 – 10.1 km from the coast. The population growth that occurred in subsequent years was due primarily to the birds’ breeding on islands closest to the coast, no farther than 2 km away from the shore. After hatching, broods from inshore islets moved to feed on coastal meadows, but nonbreeding birds and failed breeders generally remained on offshore islands for the molting period. Further expansion of the Barnacle Goose in the eastern part of the Gulf of Finland is expected. However, expansion could ultimately be restricted by the limited food resources for broods and molting birds.


INTRODUCTION
In recent decades, climate change and human activities have significantly sped up changes in the natural environment. One of the habitats especially sensitive to these changes is the shores of large waterbodies of the boreal, Subarctic, and Arctic zones. Studies of wildfowl adaptations to the changes within their environment are thus of particular interest. In particular, such adaptations include changes in bird distribution and migration that lead to completely new types of nesting habitats.
For most of the 20th century, Barnacle Goose (Branta leucopsis) bred only on the islands of the High Arctic: on the northeastern coast of Greenland, on Spitsbergen and Vaygach Islands, and on the southern island of the Novaya Zemlya Archipelago (Ptushenko, 1952;Cramp and Simmons, 1978;Ganter et al., 1999). At that time, most of the birds nested on the coastal rocky cliffs (Menzbir, 1895;Ptushenko, 1952).
A severe decline of this species was observed in the middle of the last century (Borodin et al., 1984). In the 1950s, the Arctic-breeding Russian population of Barnacle Geese was estimated at 10 000 individuals (Boyd, 1961). The nuclear weapon testing actions carried out by the Soviet Union in the Novaya Zemlya archipelago from the 1950s to the 1990s had a serious impact on the biota of the Arctic. In the 1950s and 1960s, numerous atmospheric nuclear tests, including the most powerful nuclear explosion in world history, were done on the southwestern part of the North Island, near the South Island of Novaya Zemlya (Khalturin et al., 2005). The main colonies of the eastern European population of Barnacle Geese were located there at that time. It is obvious that terrestrial and sea ecosystems and their components, including polar bears (Ursus maritimus) and huge seabird colonies, suffered heavily from the blasts and excessive radiation there (Borodin et al., 2001). The catastrophic decline of the Atlantic herring (Clupea harengus) population can also be associated with these nuclear tests because feeding grounds of this species are located in the eastern part of the Barents Sea close to the archipelago (Krysov, 2000).
The early 1970s saw intensive growth in the numbers of wintering and migrating Barnacle Geese in the western Baltic, and small groups of birds began to stay on the coasts of the Baltic Sea during the summer (Owen, 1997;Ganter et al., 1999). The first nesting in this region was registered on a small island near Gotland Island (Sweden) in 1971 (Larsson et al., 1988;Black et al., 2014). Later, breeding Barnacle Geese appeared on the western islands of Estonia and southern Finland (Leito, 1996), as well as in the Danish Archipelago (Olsen, 1992;Mortensen and Hansen, 1999). Nesting colonies of Barnacle Geese were found in the Netherlands in the early 1980s (Meininger and van Swelm, 1994;Ouweneel, 2001;Voslamber et al., 2007) and on the coast of Germany in the late 1980s (Koop, 1998;Kruckenberg and Hasse, 2004). The number of colonies of the species grew rapidly, and in the early 2000s the nesting population of Barnacle Geese in Western Europe reached 25 000 birds in the North Sea and 21 000 in the Baltic Sea (Voslamber et al., 2007;Feige et al., 2008).
Economic activity, climate change, and nature protection measures in the regions far from the Arctic can have a significant impact on Arctic ecosystems because of migrating animals. Moreover, long-distance Arctic migrants can lead to changes in non-Arctic ecosystems. In the 20th century, the expansion of farmlands and intensive use of fertilizers allowed many species of Arctic herbivore birds to feed on plants more nutritious than their natural diet during migration and winter periods, while the spread of pesticides and natural habitat shrinkage decreased the number of carnivorous mammals and avian predators such as White-tailed Eagle (Haliaeetus albicilla). At the same time, hunting restrictions and other nature protection measures were introduced in Europe and North America. All these factors have driven population growth in a number of Arctic species and also made breeding at temperate latitudes energetically feasible for some of them (van der Jeugd et al., 2009). However, different species and populations showed different trends. The size of the Russian European population of the White-fronted Goose (Anser albifrons albifrons) has increased significantly. At the same time, the size of Greenlandic populations (A. a. flavirostris) of this species has decreased (Fox et al., 2010). Greater Snow Geese (Chen caerulescens atlantica) in North America have not only increased in number, but also changed the areas of wintering and migratory stops (Gauthier et al., 2005). In some northern regions, the growth of the population of the Lesser Snow Goose (C. c. caerulesens) has led to overgrazing and catastrophic degradation of the Arctic ecosystems (Kerbes et al., 1990). The population of Canada Goose (Branta canadensis) has also increased, and the Giant Canada Goose (B. c. maxima) has established sedentary populations in urban areas in the temperate zone, causing inconvenience to local residents (BirdLife International, 2016). The population of the Dusky Canada Goose (B. c. occidentalis) has declined over the past 30 years because Canada Geese of five other subspecies now occupy the Cooper River delta on the south-central coast of Alaska, where the Dusky was formerly dominant (Bromley and Rothe, 2003). European Bewick's Swan (Cygnus columbianus bewickii) and Bean Goose (Anser fabalis) actively use farmlands in winter; however, their populations are of conservation concern because their numbers are in decline (Fox et al., 2010;Rees and Beekman, 2010). The Barnacle Goose populaton has increased significantly; moreover, this Arctic species has colonized new habitats not only in the Arctic, but also in the temperate zone. These Barnacle Goose populations have substantial colonization flexibility. Positive and negative consequences for the newly settled ecosystems need to be studied. Gathering data on such population trends in Arctic animals is also important in connection with the impact of global climate change on the Arctic and other regions.
Many Arctic sea birds, such as Velvet Scoter (Melanitta fusca), Common Eider (Somateria mollissima), Arctic Tern (Sterna paradisaea), Ruddy Turnstone (Arenaria interpres), Ringed Plover (Charadrius hiaticula), Razorbill (Alca torda), and Black Guillemot (Cepphus grylle), are widely spread and breed in the eastern part of the Gulf of Finland and in the Baltic Sea (Cramp and Simmons, 1978;Malchevsky and Pukinsky, 1983;Bubyreva et al., 1993;Noskov et al., 1993;Iovchenko et al., 2002;Shilin et al., 2014;Cherenkov et al., 2016). Most of these species in the Baltic Sea are probably relics of the last glacial period (Malchevsky and Pukinsky, 1983). In contrast to this group of birds, for Barnacle Geese there is no evidence of breeding in the Baltic Sea in previous centuries. It is therefore probable that the recent establishment of the Barnacle Goose represents an introduction of the species into an entirely new region.
The nesting and migration of Barnacle Geese in the Russian part of the Gulf of Finland and in the other territories of northwestern Russia have been discussed in several papers (Kouzov and Kravchuk, 2008;Sagitov et al., 2010Sagitov et al., , 2011Sagitov et al., , 2012Sagitov et al., , 2013Sagitov et al., , 2014Hohlova and Artemiev, 2015;Agafonova, 2016); however, the overall coverage of this issue remains quite fragmented. In this paper, we present a new detailed study of Barnacle Goose nesting patterns in the Russian part of the Gulf of Finland.

METHODS
Data on nesting Barnacle Geese were obtained during the long-term studies of waterfowl in the eastern part of the Gulf of Finland conducted in 1987 -2016 by the authors of this paper together with their colleagues from St. Petersburg State University, the Zoological Institute of the Russian Academy of Sciences, and the Baltic Fund of Nature. The research expeditions covered the Soikinsky and Kurgalsky Peninsulas; the archipelagos of Seskar, Virginy, Dolgy Reef, Dolgy Kamen, and Bolshoy Fiskar; and the islands of Moshchny, Maly, Vigrund, Gogland, Rodsher, Maly Tyuters, Bolshoy Tyuters, Sommers, Nerva, Ryabinnik, Maly Fiskar, Gusiny, and Stoglaz. Khitomatala and other islets, including Kurgalsky Reef, Tiskolovsky Reef, Vigrund, Vestgrund and Vikkala, were also covered. Note that until the late 1980s, a strict border regime in all these territories prevented any ornithological research.
The Kurgalsky Peninsula was studied in 1987 -99 and then later from 2005 to 2016. Detailed surveys of nesting birds and broods on the inshore islands (Dolgy Reef, Bolshoy Fiskar Archipelago, Maly Fiskar, Tuman) of the coast were usually conducted at least two times per summer season. Initial information about the birds on the islands of the Gulf of Finland was obtained during the short-term expeditions of the St. Petersburg State University conducted in 1991-92 and 1994(Noskov et al., 1993Buzun, 1997;Iovchenko et al., 2002). In 2005 -08, Anna Rychkova conducted stationary surveys of nesting and migrating birds in May -July on Seskar Island (Rychkova, 2014) and on Bolshoy Fiskar.
In the remaining areas of the Gulf of Finland, research was conducted as part of ship expeditions with shortterm landings on the islands. In 2005 -06, these studies were carried out by the St. Petersburg State University expeditions. In 2010 -14, two ship expedition teams organized by the Baltic Fund of Nature and St. Petersburg State University made counts of nesting birds on islands (Sagitov et al., 2010(Sagitov et al., , 2011(Sagitov et al., , 2012(Sagitov et al., , 2013(Sagitov et al., , 2014. During these years, three expeditions lasting 6 -12 days were usually conducted between the end of May and the end of July covering all the island areas of the eastern part of the Gulf of Finland. In 2015, during the period from 19 May to 25 June, three expeditions investigated the islands of the northern coast of the Gulf of Finland, Bolshoy Tyuters Island, and the Seskar Archipelago. The duration of these trips ranged from 3 to 14 days. In 2016, during the period from 28 May to 31 June, two expeditions counted nests, broods, and nonbreeding birds on the islands of Moshchny, Vigrund, Maly Tyuters, Rodsher, and on the Virginy Archipelago. The dense zigzag total count was conducted on smaller islands with areas of 1 -12 hectares. Only the coastal strip was inspected in detail on the large islands (Bolshoy and Maly Tyuters, Moshchny, and Maly).

Barnacle Geese Settlement in the Region
Until the end of the 1980s, birds belonging to the Arcticbreeding Russian population of Barnacle Geese were rarely observed migrating through the Leningrad region and Karelia (Putkonen, 1940;Neufeldt, 1970;Malchevsky and Pukinsky, 1983). Their migration was also hardly ever observed in the Arkhangelsk region in the mid-20th century (Belopolsky, 1956). However, beginning in the 1960s, researchers started to observe intensive autumn migrations of the species at various sites along the coast of the White Sea: in the White Sea straits, on the eastern shore of the Onega Peninsula (Kishchinsky, 1979), and on the southwestern shore of Onega Bay (Kumari, 1963).
The number of migrating Arctic-breeding Barnacle Geese began to increase in the eastern part of the Gulf of Finland in the late 1980s (Bubyreva et al., 1993;Kouzov, 1995). In the following decade, this species became a mass migrant in the area (Buzun, 1998;Kouzov, 1995;Vasiljeva, 2002;Kontiokorpi and Rusanen, 2014). During these years, mass spring migratory stopovers of Arcticbreeding Barnacle Geese started to form in the vicinity of the town of Olonets in South Karelia, on the north coast of Ladoga Lake (Zimin et al., 2002;Lapshin et al., 2016), and at the mouth of the Northern Dvina River by the White Sea (Andreev, 2005). In recent years, the Barnacle Goose has become one of the greatest mass migrants in the eastern part of the Gulf of Finland (Kouzov, 2009(Kouzov, , 2010Kouzov and Kravchuk, 2010;Kouzov and Loseva, 2014), in South Karelia (Artemiev et al., 2009(Artemiev et al., , 2011, and on the Onega Peninsula of the White Sea (Volkov et al., 2015).
On 22 June 1995, a Barnacle Goose nest with a clutch of six eggs was found on Dolgy Reef Island on the northern coast of the Gulf of Finland near the Russian-Finnish border (Gaginskaya et al., 1997). Some birds might have begun to nest in the region earlier, but as the islands of the Russian part of the Gulf of Finland were under a strict military regime, it was extremely hard to study all the islands regularly before the 1990s.
By 2006, the breeding population of this species on the northern coast of the Gulf of Finland had increased to 31 pairs. Nests were found on the islands of Maly Fiskar, Dolgy Reef, and on the Bolshoy Fiskar Archipelago (Table 1). Several dozen nonbreeding individuals were observed there as well. In 2006, one Barnacle Goose pair also bred on Reymosar Island on the western coast of the Kurgalsky Peninsula, on the southern shore of the Gulf of Finland (Kouzov and Kravchuk, 2008).
In 2010 -12, the number of Barnacle geese nesting in the Russian part of the Gulf of Finland varied from five to 25 pairs (Sagitov et al., 2010(Sagitov et al., , 2011(Sagitov et al., , 2012(Sagitov et al., , 2013(Sagitov et al., , 2014our data). Not all islands were visited in 2010, so some nests could have been missed on unvisited islands. However, some expansion of the nesting area was noted. In 2010, nesting of this species was noted on Rodsher Island in the central part of the Gulf of Finland, 16 km to the west of Gogland Island. In 2011, nesting pairs of Barnacle Geese were first found on Ryabinnik, Malaya Otmel, and Galochy Islands on the northern coast of the Gulf of Finland. In 2012, two pairs bred on offshore Nerva Island (Table 1).
In 2014 -15, largely the same group of islands was observed as in 2011 -13 (Sagitov et al., 2010(Sagitov et al., , 2011(Sagitov et al., , 2012 Islands  1995  2005  2006  2010  2011  2012  2013  2014  2015  Total   Rodsher  -1  --1  0  0  0  0  0  1  Dolgy Reef  1  -22  1  5  4  1  5  8  47  Zapadny Greben  0 (Table 1). In these years a further expansion of the nesting area in the northern part of the Gulf of Finland was observed. In 2014, Barnacle Geese started to reproduce on Vostochny Greben and Kamennaya Zemlya Islands, and in 2015 on Zapadnyy Greben, Tuman, and Stoglaz Islands (Khrabryi and Baibekova, 2016; our data) (Figs. 1, 2). In 2010, Barnacle Geese started to breed on large lakes located to the east of the Baltic Sea. The first nesting of two pairs of this species on Ladoga Lake was recorded on the islands of the Valaam Archipelago. The number of breeding birds in the area was constantly growing: in 2013 as many as five pairs were nesting there (Agafonova et al., 2016). In 2015, the first nesting was recorded on Dedova Plesh Island in the southwestern part of the Kizhi Archipelago (Onega Lake) (Hohlova and Artemiev, 2015).

Spatial and Landscape Distribution of Nesting Birds
All known cases of nesting Barnacle Geese in the boreal zone of northwest Russia are confined to the three largest waterbodies of the region, namely the eastern part of the Gulf of Finland and Ladoga and Onega Lakes. The majority of nests were found in the northern parts of these waterbodies on the border of the Baltic crystalline shield. These are regions with predominantly esker landscapes smoothed by glacial granite rocks, characterized by a heavily rugged shoreline and numerous coastal islands (skerries).
In these areas, Barnacle Geese nest mostly on rocky, forest-free islands. The size of these islands is 0.7 -9.4 hectares, with an elevation of 3 -12 m, and the distance to the mainland is 0.4 -28.3 km ( Table 2). Because of the sharp depth depression, the shallow zone around these islands is largely absent. The prevailing depths in the Gulf of Finland near these islands vary from 5 -10 m to 10 -40 m ( Table 2).
The majority of the nests were recorded on Dolgy Reef Island, as well as on Maly Fiskar Island and the Bolshoy  (Table 1).
In the Russian part of the Gulf of Finland over the past 25 years, only two cases are known of nesting outside the landscape zone described above, and they are clearly an exception to the rule. In 2006, one pair nested on Reymosar Island, a boulder-sand moraine island on the southern coast of the Gulf of Finland, and in 2010 a pair nested on Rodsher Island, a boulder-pebble moraine island at the center of the Gulf of Finland, 17.7 km southwest of Gogland Island. In the following years the birds did not breed there.
On the Valaam Archipelago of Ladoga Lake and on the Kizhi Archipelago of Onega Lake, all Barnacle Goose nests were also found on smaller high rocky islands (Hohlova and Artemiev, 2015;Agafonova et al., 2016). On the Valaam Archipelago, birds occupied only rocky forest-free islets, or ludas (Agafonova et al., 2016). However, there were several pines on Dedova Plesh Island on Onega Lake, where reproduction of Barnacle Geese was observed in 2015 (Hohlova and Artemiev, 2015).
As can be seen from Tables 1 and 2, until 2010 Barnacle Geese nested in the eastern part of the Gulf of Finland almost exclusively on the islands lying at a distance of 2.4 -10.1 km from the coast. In subsequent years, the population growth was primarily due to the birds inhabiting the islands closest to the coast, no farther than 2 km from the shore (Fig. 3). In 2014 -15, 48% of all breeding birds in the area nested on inshore islands. Nesting density was also higher there. In 2015, the nesting density on offshore islands, that is, those lying at a distance of more than 2 km from the coast, was 1 nest per ha, and density on inshore islands, located within 2 km of the shore, was 2.6 nests per ha (t = 2.38, N1 = 8, N2 = 9, p < 0.05). The average sizes of the inshore and offshore islands were 3.5 ha and 4.2 ha, respectively. The sizes did not differ significantly (t = -0.43, N1 = 8, N2 = 9, p > 0.05).

Distribution of Nests in Microhabitats
Almost all nests of Barnacle Geese (n = 137) described in detail in 2010 -15 in the eastern part of the Gulf of Finland were located in the interior parts of the islands, far from the oversplash zone. Depending on the size of the island, the distance from the nest to the shoreline varied from 12 to 40 m (mean 23, SD 7 m). The elevation of the nest locations varied from 1.7 to 11 m above the water (mean 3.4, SD 1.9 m). In all the years of research, only two nests (1.4%, n = 137) were found within the lower level of the rock base. Most nests (77%, n = 137) were located at the middle level of cliffs. Only 21% of all nests were located at the upper level of rocks.
All nests found at the upper level of rocks were located on smooth plateaus and were uncovered, residing in the microdepressions of the substrate on the bare rocky ground or among scarce low-level vegetation (Table 3). All nests in the middle level were found in relief depressions in the inner area of the islands. Most of these nests were located in wide valleys or on wide ledges between rocky banks (65% of such nests, n = 110). Only about one-third of all nests (35% of nests, n = 110) were found in narrow rock depressions (width 2 -5 m) of the middle rock level. Two nests at the lowest level of rocks were, on the contrary, found on microelevations of the relief (Table 3).
The most common nesting microhabitats were various shelters under trees or bushes, or in high grass. These microhabitats hosted 72% (n = 137) of all nests overall and up to 97% (n = 108) of all nests at the middle level of rocks. By contrast, at the upper rock level and the lowest rock level, vegetation was scarce or even lacking.

Broods and Molting Flocks
Shortly after hatching, most families with broods left the nesting islands to feed along the mainland coast. On most of the islands where nests were found, the broods recorded were mostly up to five days old. The counts made at the end of June and in July indicated that some of the older broods from islands located no farther than 5 km from the coast were widely dispersed along the mainland coast and along large inshore islands. In 2013 -15 some families of Barnacle Geese were found on the northern coast of the Gulf of Finland and on large, wooded inshore islands, at a distance of 4 -5 km from the nearest known nesting place. On the islands located more than 10 km from the coast (the Bolshoy Fiskar Archipelago and Nerva Island), broods stayed until fledging, which most often occurred in the first 10 days of August.
Molting flocks were encountered exclusively on the islands. In 2013 small molting flocks of Barnacle Geese were first observed on the Nerva (10 -12 individuals) and Dolgy Reef Islands (12 -20 individuals), and Bolshoy Fiskar Archipelago (8 -35 individuals). The birds stuck to the rocky capes, the ones that jutted out the farthest into the sea.

DISCUSSION
The expansion of the Baltic population of Barnacle Geese began much later in the boreal zone of northwestern Russia than in the western parts of the Baltic region. The first Barnacle Geese were observed breeding in the Baltic Sea on Gotland Island in Sweden (Larsson et al., 1988;   Moreover, it appears that this process is far from being completed. Just as in the western Baltic regions and in the North Sea (Kruckenberg and Hasse, 2004;Feige et al., 2008;van der Jeugd et al., 2009), nesting in the eastern part of the Gulf of Finland was preceded by observations of migrating and summer staging birds.
Whereas in the Netherlands Barnacle Geese can nest not only on the islands but also on the mainland, in the Baltic Sea the birds prefer to nest exclusively on the islands (Feige et al., 2008). This pattern, which is also typical for the eastern part of the Gulf of Finland, is due to the fact that the islands are generally free from terrestrial predators. In the Russian part of the Baltic Sea, Barnacle Geese nest mostly on small forest-free islands with areas of 0.9 -12.5 ha. Barnacle Geese inhabit islands of the same size in the other parts of the Baltic as well. In Estonia, Barnacle Geese nest on islands of 2 -5.5 ha (Leito, 1996). In Germany, they inhabit mostly small islands with an area of less than 0.02 ha (Feige et al., 2008), while in Sweden, the colonies are located both on small islands and on islands of up to 300 ha (Ganter et al., 1999).
Barnacle Geese in the boreal zone of northwestern Russia nest almost exclusively in smoothed rock landscapes. Almost all known nesting cases were on the rocky skerries of the northern coasts of the Gulf of Finland, Ladoga and Onega Lakes, in places where the Baltic crystalline shield crops out at the surface. A similar picture is observed in more western parts of the Gulf of Finland. At present, about 3000 -3500 pairs of Barnacle Geese breed on the skerry archipelagoes along the coast of Finland (Valkama et al., 2011).
Most of the birds inhabited flat platforms and hollows at the middle level of the rocks in areas with well-developed grass vegetation or under bushes. Nesting areas on Onega and Ladoga Lakes were also very similar to the maritime landscapes. This type of nesting of Barnacle Geese was dominant in the Arctic during the period of strong decline in numbers and nesting area in the mid-20th century (Uspensky, 1951;Bauer and Glutz, 1968;Cramp and Simmons, 1978;Syroechkovsky, 1995). Russian Arcticbreeding Barnacle Geese have begun to inhabit flat coastal tundra and flat inshore islands only in the last 40 years as the population growth commenced (Kalyakin, 1986;Gavrilo, 1991;Filchagov and Leonovich, 1992;Syropechkovsky, 1995;Volkov and Chuprin, 1995;Kondratyev et al., 2013). Near the southern coast of the Gulf of Finland, there is a fairly large number of small flat moraine islands with abundant grassy vegetation, which are actively used for nesting by other herbivorous wildfowl: Mute Swan (Cygnus olor), Greylag Goose (Anser anser), and Gadwall (Anas strepera); however, Barnacle Geese have not yet established themselves there.
A tendency to settle on the islands closest to the mainland shore is an adaptation of Barnacle Geese that allows them to nest in rocky habitats with poor food. After hatching, broods disperse widely along the coast. Barnacle Geese obviously breed on the islands that are closest to the mainland so that the broods have to cover only a short distance to get to the feeding habitats. In Russia, nearly half of the nests of Barnacle Geese are located on islands lying no more than 2 km away from the coast. In the Netherlands, Barnacle Geese cross a similar distance to the coast: 70 -1500 m. In Germany this distance is even smaller: 10 -400 m to the coast. However, in some areas of the Baltic Sea, broods travel more than 3000 m from the colony to the shore (Feige et al., 2008). The first single pairs of birds in the initial years of settling in the eastern part of the Gulf of Finland sought to occupy the islands most remote from the coast, which provided them with better protection from terrestrial predators. Low intraspecific food competition in those years allowed the broods to feed on the same island until fledgling. With the increase in the number of breeding pairs, the only way to optimize the use of space and food resources was to develop colonies on the islands closest to the shore or on large archipelagoes that would provide food resources for broods.
Barnacle Geese of the North Sea and Baltic Sea regions leave nesting sites after hatching takes place and usually head for the protein-rich plants of agricultural landscapes or even lawns and parks in the cities (Feige et al., 2008;Väänänen et al., 2011). In the eastern Gulf of Finland, as well, geese with broods usually leave nesting areas after hatching and move to the mainland. There are no agricultural areas near the seacoast in the Russian Baltic FIG. 3. The number of nests found on the islands located within 2 km of the mainland and on the islands lying farther than 2 km from the mainland. region, however: these shores are mostly covered by forests and bulrushes. Sea meadows are very narrow, and marshes are mostly absent. Local birds in prebreeding, nesting, and brood-rearing periods do not have the same food supplies that they would get in agricultural fields or marshes. Moreover, increased predation risk in these narrow feeding habitats near the forest influences the time and energetic budget of the feeding birds. Gulls, Hooded Crows (Corvus corone cornix) and White-tailed Eagles substantially reduce the success of nesting in the islands. Gull colonies are present on most of the islands where Barnacle Geese nest, and at least six pairs of White-tailed Eagles nest in the coastal areas of the Leningrad region (Pchelintsev, 2006). Foxes can stay on the islands and predate all the nests there, but no foxes were found on the islands observed. The pressure of predators and hunting is probably less intensive on offshore islands than on inshore ones. However, as the bird population grows, food resources become inadequate, and then the colonization of inshore islands begins. Thus the population growth of Barnacle Geese in the Russian part of the Baltic Sea is slow now in comparison with the western temperate populations, even Finnish populations that are situated very close by (Väänänen et al., 2011). The Helsinki area is special because geese can use city parks that offer good grazing grounds and safety from predators. In nearby Estonia, population growth of Barnacle Geese since establishment has been slow, as in our study area (Leito, 1996). The future growth of these nesting populations should be less significant than in the western areas of the Baltic Sea and the North Sea.
Most of the breeding areas of Barnacle Geese in the Baltic and North Sea regions are protected areas (Feige et al., 2008). However, in the Russian Baltic Sea, almost none of the goose nesting areas have protected status. In Sweden, half of the nesting areas of Barnacle Geese are protected, and the other half are located in areas formerly used for military purposes (Feige et al., 2008). In the east of the Gulf of Finland, in Russia, Barnacle Geese breed mainly within a closed border zone, where the level of disturbance is low. However, with the removal of borderline restrictions, a significant increase in the tourist flow and disturbance of birds may take place. Therefore, the establishment of protected areas is of crucial importance for the conservation of bird populations nesting on islands in the Gulf of Finland. Since the 1990s, work has been underway to establish a nature reserve, which would include most of the islands important for nesting of waterfowl in the eastern part of the Gulf of Finland. On 21 December 2017, the "East of the Gulf of Finland Reserve" was established. This reserve will help to preserve the unique conditions for the nesting of geese and other waterfowl on the islands of the eastern part of the Gulf of Finland.