Weather conditions, distribution of resources feed and dynamics of the spatial structure of the Great Cormorant in the water area of Lake Baikal

. On the basis of long-term observations (2018-2023), the features of the distribution of the Great Cormorant in the water area of Lake Baikal during the mass rise of young birds “on the wing” are considered, depending on the distribution of feed resources and the state of weather conditions. At this time, young birds do not yet have experience of independent food production and parents feed them for 10-15 days. In this regard, the availability and abundance of feed resources is very important for birds. Our observations revealed large, but temporary concentrations of birds in areas of high abundance of feed. Large concentrations of birds are also formed in places convenient for recreation during long periods of adverse weather conditions (from 3-4 to 6-7 days) – strong winds. Such clusters can reach several thousand and even several tens of thousands of birds. They form quickly and also disappear quickly as more favorable conditions are restored on other parts of this lake. This feature of the behavior of birds must be taken into account when carrying out accounting work on large areas, which include snd the water area of Lake Baikal. Accounting of birds from a launch along the coastline, with a detailed survey of colonies in places of their concentration, is the only acceptable method of monitoring the state of the population of the Great Cormorant on Lake Baikal.


Introduction
Currently, the Great Cormorant Phalacrocorax carbo is one of the most widespread species of coastal birds of Lake Baikal.This is a typical highly specialized ichthyophage and the state of fish resources actually determines the features of its distribution within the area.In Eastern Siberia, it is characterized by age-old dynamics of the area associated with cyclical climate variability.At the beginning of each century cycle, usually occurring at the beginning of the century, the water level of Central Asia is very low (the warm-dry phase of the century-old climate) and a large number of shallow and small lakes completely dry up.On large lake systems, the belt of shallow waters practically disappears, which leads to a sharp reduction in the area of spawning grounds and feeding areas of carp fish.Due to a strong reduction in the reproduction of fish resources and the area of wetland ecosystems, the Great Cormorant is forced to move to the northern border of its range and its number in the basin of Lake Baikal, as well as along the cascade of Angara reservoirs, increases sharply [1][2].During this period, it becomes one of the most numerous bird species in Eastern Siberia.In the future, as the age-old climate cycle develops, the water level of the southern parts of the area of this species is restored.It remains nesting in more southern areas, and in northern areas its abundance is sharply reduced, up to almost complete extinction of the species.
During the XX century, the abundance of the Great Cormorant was high throughout its first half, and then the number of this species began to decline sharply [3].From the 70s of the last century to the beginning of the current century, it was marked here only by very rare flights (no more than 2-3 meetings of single individuals during the summer season).However, at the beginning of the XXI century, its number increased sharply, and since 2006 it began to nest constantly on Lake Baikal [2,4], which was undoubtedly due to the strong warming in Central Asia and the development of very large, prolonged and extreme droughts [5].It was at this time that the mass eviction of birds to the northern border of the area occurred, and with the last wave of settling shorebirds and waterfowl, a Great Cormorant appeared on the lake Baikal [6].He very quickly mastered the places of former nesting sites (within 5-6 years) and began to displace the Mongolian Larus (vegae) mongolicus and the Common Larus canus of Gulls from them [7].
Despite the high visibility and the formation of large colonies and forage clusters, accounting for this species is fraught with great difficulty.A significant part of the population of the Great Cormorant is represented by young individuals who have not yet reached puberty.In addition, with a high death rate of clutches, which is characteristic of the Baikal population of the Great Cormorant, the number of birds that have stopped nesting gradually increases during the breeding season.Such birds often stay in colonies, occupying areas free of nests.It is very difficult to distinguish them from birds with a successful breeding season, with short-term observations.Therefore, counting nests in the second half of nesting is often very difficult, and sometimes impossible.In this regard, the solution of issues related to the organization of monitoring of the abundance of this species requires special work to clarify the influence of factors determining the abundance of the species in different areas of large territories [8].This paper presents materials reflecting attempts to solve this problem.

Research area, material and methodology
Lake Baikal is one of the largest inland freshwater lakes in the world.Its length reaches 636 km, width 79.5 km, depth 1637 m, and the area of the water mirror is 31500 km 2 .In the water area of the lake there are 22 islands (often separate rocks devoid of vegetation) and the largest of them (Olkhon Island) has an area of 700 km2 [9].The lake is the central link of the Baikal rift zone, the formation and development of which occurs simultaneously with the world rift zone [10].The total length of the Baikal Rift zone exceeds 2000 km and it is the Baikal zoogeographic boundary in the distribution of flora and fauna of Inner Asia.The climate of the lake basin is characterized by a milder character, compared with the surrounding territories characterized by continental climatic conditions, and can be attributed to the seaside.It is characterized by milder winters and cooler summers.In comparison with the surrounding territories on the coastal plains of the lake, the seasons are almost a month late [9].Nevertheless, its climate is characterized by rather harsh conditions and the coefficient of its continentality (according to Cenker) from south to north increases from 62 to 64 [9].
A characteristic feature of the lake.Baikal are strong winds having different directions.But the strongest storm winds are typical for the spring and autumn periods.In summer, their intensity decreases, but the duration of sustained winds can be several days [9].In this regard, it is possible to form large concentrations of birds from the leeward side along the most favorable for recreation areas of the shores of Lake Baikal.There are cases of formation of short-term concentrations of feed resources, which, first of all, attract a Great Cormorant.Usually, they are associated with the course of fish to spawn or its accumulation at feeding sites.As a rule, such places are large shallow and well-warmed bays and straits of Lake Baikal in summer [2,4,[7][8]11].They are places of concentration of colonies of the Great Cormorant and several species of Gull birds (Maloe More of Strait, Chivyrkuysky Bay, Proval Bay, Posolsk Litter).
Long-term observations show that birds stay in shallow waters along the shore of Lake Baikal, bounded by an isobath of 10-12 m. [12].It is here that Great Cormorants are concentrated for most of the open water period.At the same time, hiking along the coastline in most of the territory is almost impossible.Rocky cliffs, a very narrow coastal strip, slippery rocks and boulders make it very difficult to move and distract from the main work.Consequently, the records must be carried out using a Launch and only during periods of relatively weak excitement (mainly in summer), Motorboats can be used.
The method of accounting for birds from water transport was developed on the basis of long-term observations [12].The methodology was based on long-term work covering the entire water area of Lake Baikal -more than 10,000 km of accounting routes.Launches of various types and modified Launches based on a standard Launch were used "Yaroslavets".They have shown good stability on a strong wave, they can cross Lake Baikal in different directions, avoiding prolonged bad weather (strong, sometimes stormy, winds).During periods of very strong storms, the vessel is defended in places convenient for parking.At the same time, leaving the bad weather, it is often necessary to cross the lake Baikal and stop at convenient places on the opposite shore.
The distance of bird detection and their precise determination on Lake Baikal strongly depends on weather conditions that limit the range of bird detection.In some cases, accounting is possible at a distance of up to 3 km.However, only a very experienced accountant can accurately determine the species at such a distance.Details of the plumage coloring of birds remain unknown, but determination is possible by the size, silhouette of a flying bird, the shape of a flying flock and the nature of the flight of the species being determined.The last sign at a considerable distance is the most accurate, but it is available only for very experienced accountants with many years of experience in such work.
Our long-term research shows that birds far from the coastline appear very rarely.They are found here only during migrations and recreation [12].Over the past 5 seasons of bird registration on Lake Baikal, we have recorded more than 5,500 sightings of a Great Cormorant at various distances.The calculation of the population density of the species was carried out on the basis of general recommendations for the registration of birds by route method.The original formulas for calculating the population density of birds and the features of their use, as well as the calculation of errors of this indicator are given in a special work [13].For a deeper study of the methodology of accounting work and the calculation of special accounting indicators, we refer the reader to the original study [14].The species composition of birds and the order of their description are given according to the latest reports of Russia and Siberia [15][16].

Results
The most common situations that cause significant movements of the Great Cormorant across Lake Baikal are associated with the formation of large concentrations of the most E3S Web of Conferences 463, 02004 (2023) EESTE2023 https://doi.org/10.1051/e3sconf/202346302004preferred food.As a rule, such movements are associated with seasonal redistribution of feeding stocks of mass fish species.For the period of our work, the movement of the Black Baikal Grayling Thymallus arcticus baicalensis on Northern Baikal to the coast of the Barguzinsky Nature Reserve -Sosnovka Bay is important [17][18].During the period of its mass movement in 2018, the main part of the birds of this species from the colonies of Goly Kyltygey and Shaggy Kyltygey of the Chivyrkuisky Bay with a total number of about 25.0 thousand birds flew to Sosnovka Bay to feed (Fig. 1).Here they rested on the coastal sandbank and dried their wings.Their total number during rest along the coast of this bay was at least 6.0 thousand birds.The basis of them, undoubtedly, were birds from Chivyrkuisky Bay.Observations of colonies during censuses showed that birds in groups of up to 300 or more birds flew towards this bay, located relatively close to the nesting sites.During the Launch trip and counting birds along the coast, migrating flocks of Great Cormorants were recorded heading to Chivyrkuisky Bay, and at the colonies, flocks of Great Cormorants arriving with food were previously recorded, corresponding in size to the flocks that had previously flown away to feed.Observation data, as well as materials from recording migratory birds during their passage to Sosnovka Bay, indicate that birds flew here from colonies on the large islands of this bay.At the same time, birds of small colonies located far from its entrance fed in the same bay in scattered groups of up to 10 birds and dried their wings here, both in the colonies and on the rocks of small capes.
According to ichthyologists, the Black Baikal Grayling approaches this bay from Northern Baikal [17][18].Migrating flocks of Cormorants were visible along the entire route E3S Web of Conferences 463, 02004 (2023) EESTE2023 https://doi.org/10.1051/e3sconf/202346302004from Chivyrkuisky Bay to the northern border of the Barguzinsky Nature Reserve.The main part of them flew along the coast, and were clearly associated with this bay, where a very large concentration of birds was discovered on the first two islands.On Goly Kyltygei, within the rocky cliffs and on the trees, there was practically no place free from birds.They sat very densely, occupying all areas free from nests.It is very characteristic that during take-off, which is not always associated with flushing of birds, birds rose from such areas in one group and flew off in a flock, which indicated their stronger connections compared to simple food aggregations.We noted flocks of the same size along the route along the coast, flying towards the bay or flying away from it.It is characteristic that when approaching the bay from the south, we did not observe migrating flocks of Great Cormorants.All this emphasizes that the movements of the birds were associated precisely with the feeding patch that formed in Sosnovka Bay.
The behavior of the birds, the nature of the places occupied in the colony (free areas between clusters of nests), the formation of dense groups, indicates that these were birds no longer participating in reproduction.Undoubtedly, the bulk of them were represented by young immature individuals (this species begins to reproduce at the 3rd year of life).At the same time, it is possible that they also included birds with an unsuccessful nesting season, who lost their nests at different stages of the breeding cycle.As is known, the death of nests in this species on the Lake Baikal is very high and a fairly significant part of birds lose their clutches early [7,19].Some of them begin to nest again, but the absence of very late broods or their very small number indicates that compensatory breeding in the Great Cormorant in the waters of Lake Baikal does not play a significant role in maintaining the population size.
It should be noted that a relatively small number of flocks flying from the eastern shore to the western one crossed the central part of Lake Baikal and went at an angle to the more southern part of the opposite shore.It is possible that they could fly here from the colonies of the Maloye More Strait.However, it is more likely that these were immature individuals moving freely around Lake Baikal.Most likely, they are the ones who find temporary food aggregations.The remaining birds, following them, begin to develop such areas of temporary concentration of abundant food.Of the total number of flocks (54) registered during the transition from Chivyrkuisky Bay to the northern border of the Barguzinsky Nature Reserve, 12 (22.2%)went to the opposite side of the lake Baikal.
A number of observations indicate that birds from the colony on Baklany Kamen (Peschanaya Bay), at least some of them, fly to feed to the Goloustnaya river delta.When passing by boat from Peschanaya Bay to the village of Bolshiye Koty early in the morning of August 28, 2018, small groups of Great Cormorants overtook the Launch and flew along the coast, without forming food concentrations in small bays and bays.At the same time, in the Goloustnaya river delta we found feeding aggregations of 30-40 birds, and sometimes more, located mainly in the north-eastern bays, i.e. at the first convenient sites along the birds' route.
Consequently, the flight of birds to feed can be very large and amount to tens of kilometers.First of all, this applies to immature birds kept in the colony, but it is possible that birds feeding their chicks can fly far from their nesting sites.Irrefutable evidence of this is the flocks of birds flying from Chivyrkuisky Bay to Sosnovka Bay to feed on August 19, 2018.We also noted feeding aggregations of Great Cormorants, far from the locations of the colonies, in other areas of Baikal (Proval, Posolsky Sor, Maly Soro bays, the mouth of the Buguldeika River, the mouth of the Sarma River, the mouth of the Verkhnyaya Angara River, the mouth of the Kichera River) (Fig. 1).
No less important in the redistribution of birds across the waters of the lake Baikal also has very strong, often stormy winds.Under normal conditions, flocks of Great Cormorants, formed by single birds, rest on sand spits and shallows, forming very dense flocks.In this E3S Web of Conferences 463, 02004 (2023) EESTE2023 https://doi.org/10.1051/e3sconf/202346302004they differ from the feeding aggregations of this species, in which the birds stay more sparsely, with an increased distance between individuals.Very often, especially in areas of small colonies, they feed and rest alone or in small groups.At the same time, when large food concentrations are detected, after changing brooding partners, birds free from brooding break away from the colony and fly to them in flocks that are practically no different from single birds.
The Great Cormorant always makes nests on the leeward side of rocky cliffs.The densest areas of the colony form on the side that is least exposed to very strong winds.The location of nests is determined by the morphostructure of rock cliffs [8].Typically, birds use tectonic fracture lines in rocks with mismatched edges and rocky outcroppings suitable for making nests.Therefore, the location of nests often has a bizarre shape, quite chaotic (obligate-colonial appearance) and with several centers of their concentrations.Nonbreeding birds often gather here to rest and occupy areas of the colony not used for nest construction.Therefore, counting nests, especially in the middle of the breeding season, is often very difficult.The nests are trampled by the chicks, the edges merge, and their tray is often not expressed [8].In this regard, counting pairs is not always possible, since the proportion of young (non-breeding) birds in the colony can be very high (up to 30.0% or more).
These young birds are not always members of a particular colony.Long-term observations show that their share varies significantly on different days and periods of colony development.But it can increase especially sharply during periods of strong winds.This indicates that non-breeding birds do not stick to specific colonies and may choose resting areas rather randomly.Strong winds that persist for several days lead to the redistribution of young birds throughout the waters of Lake Baikal.This is probably to the same extent characteristic of birds that have lost clutches or chicks and are freed from parental care.We have repeatedly observed flocks of birds crossing Lake Baikal during periods of unfavorable weather.However, it is impossible to trace their route and therefore it is difficult to definitely say that they go to the other, leeward, side of Lake Baikal.
At the same time, long-term work and constantly windy weather repeatedly created opportunities to understand the essence of the observed processes.In a strong wind on August 16, 2018, we were forced to leave the Selenga river delta, because it was impossible to work here in such conditions.During the transition, 3 flocks of great cormorants (up to 300 birds each) left the eastern shore for Baikal, and on the approach to the Olkhon Gate in the evening, two flocks of birds of this species (70 and 120 birds) were observed flying from Baikal to the shore.Birds hunting for fish on such a wave in open water is completely excluded.While walking along the shore, we repeatedly encountered flocks of Ccormorants, judging by the direction they were flying from Lake Baikal, but it was not possible to definitively answer the question of whether they were related to the flight across the lake.
In 2023, while counting coastal birds in the waters of Lake Baikal on July 26, we had to leave Proval Bay (delta of the Selenga River) early in the morning of July 27 due to a very strong northeast wind.On the transition to the village of Turka, one flock of Great Cormorant was encountered, leaving for Baikal (30 birds).The strong wind continued the next day.Just beyond Turka, near Cape Tonkiy, on July 28, we noted flocks of birds leaving for Baikal: 120, 25, 4 and 300 individuals.Making a very large circle, skirting the shallow waters of the cape, we were able to follow the flying birds.A large dense flock of 300 birds was visible for a very long time and, without a doubt, the birds went to the opposite leeward side of Lake Baikal.
On the same day, when entering the Chivyrkuisky Bay at the junction of the cold waters of Baikal and the warm water of the bay, a huge concentration of Great Cormorants was discovered -about 8.0 thousand birds.It was stretched along the ribbon of water junction E3S Web of Conferences 463, 02004 (2023) EESTE2023 https://doi.org/10.1051/e3sconf/202346302004and the birds, gradually moving along it, went into the bay.The colony of the Great Cormorant on the island of Shaggy Kyltygei was very densely occupied and included at least 20.0 thousand birds, which clearly exceeded its usual size.At the same time, on Goly Kyltygey, the first island in the bay open to all winds, only 350 Great Cormorants and 250 Mongolian gulls were counted.The entire bay was filled with actively feeding birds, which had not been observed here before.
The next day, July 29, 2023, with continued but somewhat weaker winds, we left for the Ushkany Islands.In the evening, the wind increased noticeably and all the way along the Chivyrkuisky Bay to the village of Monakhovo (the upper part of the bay) and back to the Launch parking place at the entrance to the bay, a continuous flight of a Great Cormorant was observed, going to the calm water at the top of the bay, and to the lake among the swamps, surrounding this area.On the morning of July 30, we reexamined Shaggy Kyltygey and counted 22.5 thousand Great Cormorants there.The rocky cliff and trees were very densely occupied by birds, but when approaching the island to continue working using a quadcopter, most of the birds left it.Apparently they are afraid of the sound of a flying machine.
In the following days, the gusts of wind decreased, but it still continued for 4 days.After going around Northern Baikal along the northwestern shore, we entered the Maloye More Strait on August 2, 2023.The excitement in the strait was great, but gradually decreased in its southern part.Bird counts on the colonies of islands and capes showed that the number of birds was lower than their abundance usually observed here -3336 birds.There was a clear absence of non-breeding birds in the colonies, which is especially evident on Bolshoy Toynik Island, which is distinguished by a high number of birds of this species.Only 110 Great Cormorants were counted here, but previously there were up to 1000 or more birds here.
There is no doubt that the spatial structure of the Great Cormorant on Lake Baikal is highly dynamic and is completely determined by weather conditions, as well as the distribution and availability of food resources.In harsh weather conditions with strong winds that last for several days, a significant part of the birds, mainly immature individuals and birds with an unsuccessful nesting season, move to the leeward side of Lake Baikal, where more favorable conditions for their feeding and rest are created.

Discussion
In connection with the facts discussed above, the peculiarities of weather conditions and the distribution of food resources must be taken into account when organizing surveys of the Great Cormorant.Until now, these counts were carried out by different specialists, each of whom had their own idea of methodological approaches to determining the abundance of this new species for Lake Baikal [4,[6][7][19][20][21][22][23].As a result, censuses carried out at different times do not agree well with each other, since changes in the number of Great Cormorants in different areas of Lake Baikal were not taken into account.Meanwhile, short-term changes in the feeding situation and weather conditions can make significant adjustments to the distribution of this species in its different areas.They must be taken into account when determining the number of species, since during the work of different groups in different periods, large errors may occur associated with both overestimation and underestimation of the total number of birds.
The main reason for the high mobility of birds is associated with their very complex age structure.Due to the late entry into reproduction (only in the third year of life), Great Cormorants have a very high proportion of non-breeding birds (up to 30.0% or more) [8,20].In addition, a number of natural factors, the development of which, in many cases, is due to the anthropological influence on the ecosystems of Lake Baikal, caused a sharp E3S Web of Conferences 463, 02004 (2023) EESTE2023 https://doi.org/10.1051/e3sconf/202346302004decrease in the breeding success of ichthyophagous birds.First of all, they are associated with a sharp reduction in the number of fish resources and pronounced starvation of the Great Cormorant chicks and large species of Gull birds [7,19,21].The consequence of this is the development of kleptoparasitism among all species of Gulls and, to a lesser extent, in large species of Gulls, destruction of nests with eggs and chicks of their own species (compulsive predation) and cannibalism.The extreme expression of cannibalism is sophisticated predation -adult birds kill the chicks of their own species, cut them up and eat them.In these cases, almost adult Great Cormorant chicks are specifically persecuted, which, despite their large size, do not have defensive reactions against cannibal attacks.
The extreme expression of cannibalism is sophisticated predation -adult birds kill the chicks of their own species, cut them up and eat them.In these cases, almost adult Great Cormorant chicks are specifically persecuted, which, despite their large size, do not have defensive reactions against cannibal attacks.Namely, in connection with this, there is a high dynamism of the spatial structure of birds that are not tied to colonies by the need to care for eggs and chicks (immature birds and adult birds that have lost eggs or chicks).Their free redistribution throughout the waters of Lake Baikal contributes to the rapid development of the most favorable feeding and weather conditions and the use of the most productive areas of this lake.In this regard, it should be noted that the most favorable conditions are found in the Chivyrkuisky Bay, where the highest number of birds is recorded.Its small width, in comparison with the neighboring Barguzin Bay and the Maloye More Strait, as well as its large length, allow Great Cormorants to use it even under the most unfavorable weather conditions, which is especially emphasized by our observations in 2023.It should be noted that in previous years there active movements of birds were observed, but they were less noticeable.
In this regard, our censuses, carried out over a relatively short period throughout almost the entire water area of Lake Baikal, make it possible to level out large differences in the number of birds in its different areas.At the same time, they make it possible to identify the main factors responsible for errors in determining the number of birds.A complete census throughout the entire water area of Lake Baikal, carried out before the birds began leaving for wintering grounds in 2023, fully confirmed the validity of our approaches to estimating the abundance of the Great Cormorant in this large inland body of water [12].Counting birds from a Launch along the coastline, with a detailed examination of colonies in places of their concentration, is the only acceptable method for monitoring the condition of the Great Cormorant population on Lake Baikal.

Conclusion
Our long-term observations related to the study of the distribution, biology and ecology of shorebirds and waterfowl in freshwater bodies of water clearly show that their active foraging zone is limited to depths of 10-15 m.In this regard, when planning detailed censuses and surveys of water bodies, it is necessary focus on the area limited by this particular isobath.For deep-sea, predominantly mountain, reservoirs, it is associated exclusively with the coastal zone.This allows you to immediately begin a detailed examination without wasting time.Counting from a Launch along the shore throughout the entire water area of Lake Baikal, in combination with a detailed examination of colonies in places of their concentration, makes it possible to obtain accurate information about the number of birds after their breeding season.At the same time, amendments to the records that can be made in the event of an incomplete survey of Lake Baikal are being clarified.At the same time, the middle part of Lake Baikal with places where colonies are concentrated must be examined completely.

Fig. 1 .
Fig. 1.Features of the distribution of the Great Cormorant in the water area of Lake Baikal, depending on feeding and weather conditions.