BIRD FAUNA OF LAKE BAIKAL, ITS FORMATION, AND DYNAMICS

I.V. Fefelov

Research Institute of Biology at Irkutsk State University, P.O.Box 24, Lenin St. 3, Irkutsk 664003, Russia

The principle of typifying the bird faunas of North Eurasia according to the origin of species was suggested by Stegmann (1938). The structure and ornithogeographic regionalization of the Baikal region was considered by Gagina (1960, 1961), and a classification of habitat ranges of these birds for this territory according to geographic complexes in light of Stegmann’s concept was discussed by Dorzhiyev and Yelayev (2000). According to the just cited references, it is obvious that the regional ornithofauna, with the representatives of the Siberian faunistic complex predominating (38%) is represented by genera and species of a very different origin – there are traceable links with Central, Minor, West, Southeast and North Asia, Beringia, and Africa. It is generally recognized that the region’s contemporaneous ornithofauna shaped itself during the Quaternary period. The origin of taxa of higher-order birds at large modern scales (Neogene, and preceding geological periods) adds little to the history of separate genera and species in a particular region because of the flying ability of birds and of the dynamicity of their habitat ranges. Some questions concerning the shaping of the ornithofauna in the Baikal region were considered in earlier studies, focusing on forest and mountain complexes of birds (Matyushkin, 1976; Dorzhiyev & Yelayev, 2003). Waterfowl was discussed in a fundamental book by Krivenko (1991), who examined the middle and high latitudes of West Asia spanning the area from the Volga to the Ob' region. But the water-associated bird fauna for the Baikal region has not been analyzed to date. We believe that to understand the processes contributing to shaping the contemporaneous composition of birds, attention should be devoted to assessing the landscape-cenotic links of breeding birds. 363 bird species have been recorded for Baikal to date (Popov, 2004). The orders being most rich in species contents are Passeriformes (159 species), Charadriiformes – waders, gulls and terns (70, mainly waders), and Anseriformes – ducks, geese and swans (41, mainly ducks). There are 237 breeding species (65%), and 35 species (10%) regularly migrate across Baikal to the northern parts of West and East Siberia but do not breed here. The other species are rare migrants and visitors. Waterbirds (grebes, cormorants, ducks, gulls and terns, etc) and shorebirds (waders, herons, crakes, etc) are concentrated mainly in shallow parts of Lake Baikal (Maloye More Strait, Chivyrkuy Bay) and in river deltas, which biggest ones are deltas of Selenga River, and of Kichera & Verkhnaya Angara rivers (Mlikovsky, 2009). In the Selenga delta, 305 bird species including 117 waterbirds and shorebirds are recorded, at the northern part of Baikal – 265 including 87 waterbirds and shorebirds (Fefelov et al., 2001). Dorzhiyev & Yelayev (2000), based on the ecological links of the birds from the Baikalian Siberia, categorize them into 5 groups: forest birds, birds of open areas, of high mountains (Alpine), water and near-water, and synanthropic birds. Our version of a classification of Baikal’s birds takes into consideration, on the one hand, the occurrence of the species in particular natural zones and altitudinal zones, and, on the other, their relation to the water environment. So, in the breeding birds 58 species populate several natural zones, 12 – mountains (rocks, mountain-tundra, etc.), and 4 are urbophilous. The remaining 163 species have their habitat occurring in a definite natural zone: 94 species characteristic for the taiga zone; 49 species are “forest-steppe” ones (including species of a typical forest-steppe, deciduous forests, and forest edges), and 20 bird species of the steppes. In the region there are 79 species (33%) that are directly associated with the water environment or nest in shoreline or overmoistened stations, and 158 non-water species. Among the birds of the Baikal region not only there are endemic species, but there are no endemic subspecies as well. Even in few mountain subspecies which are characteristic for the area of Baikal, their ranges extend either into the Altai-Sayan mountain range or into the Stanovoye upland (Stepanyan, 1990). In the Baikal region, 111 bird species (one-third of the regional ornithofauna) have the periphery of the range (Yelayev, 2000). For 74 species of birds breeding in Central Siberia there are meridional disruptions of their range or contact zone of the eastern and western populations passing in the area of the Yenisei and Sayan or in the area of the Baikal rift. Most often these populations are assigned to different subspecies, but sometimes they are referred to forms of the species rank in the composition of a superspecies complex. It is assumed that they were surviving unfavorable climatic conditions in refuges lying southeast and southwest of their contemporaneous range (Matyushkin, 1976; Nazarenko, 1982). According to the degree of their divergence, the periods of their isolation were rather long-lasting. The proportion of species for which in the Baikal region there exists a junction of the ranges of subspecies, is the same for the water and non-water birds, or 17% for each. The number of species, having special subspecies in Central Asia, is smaller for the former, or 3% against 12%. The number of species having a disrupted habitat range here, is, on the contrary, much larger for the former, or 21% against 0.5%. This is of particular interest at the background of the fact that waterbird species generally have fewer subspecies than non- waterbirds (explained by Mayr (1970) with a high ability of waterbirds to change breeding places because of instability of their water habitat environment). Thus, a definite “faunistic vacuum”, as pointed out by Nazarenko (1982) for birds from broad-leaf and dark-coniferous forests of East Siberia, is demonstrated here also for birds associated with the region’s water bodies. This is dictated by the existence of zoogeographic barriers (Baikal, and mountain ranges) and landscape rearrangements during the Pleistocene (Matyushkin, 1976) as well as by the continental climate with lowered humidification. The dynamics of fauna and bird population in the Baikal region reflects primarily the dynamics of their distribution rather than of the formation of their species. According to recent research (Paleolimnological…, 1989, Team …, 2004; Tarasov et al., 2007; and other publications), during periods of Pleistocene coolings the Baikal region was dominated by birch-larch sparse forests and grass landscapes, but the taiga remained in separate refuges. Local glaciations had a mountain-valley character. Deep freezing of soils favored the existence of permanent and temporary water bodies. Such conditions are acceptable for nesting by birds from tundras and grass landscapes, many waterbirds and shorebirds, and some of forest-steppe species. During warm or moderately cold moist periods, different types of dark-coniferous taiga occurred, with the involvement of broad-leaf species; however, as a consequence of the heavily dissected mountain relief, there of course existed portions of steppes of different types. The composition of birds was likely similar to the contemporaneous one. During warm, dry interglacial periods, light-coniferous forests and steppes were expanded. That created conditions for the habitat of birds, having their origins in the southern taiga, forest steppe, and the steppe zone, including waterfowl. A climatic reconstruction (Shimarayev & Mizandrontsev, 2004) showed that the end of the Sartan cooling, between 16 and 11 thousand years ago, was characterized by deep thermal cycles, having no equal in the Holocene, recurring at intervals of about 1 thousand years. At cycle maxima, temperatures approached contemporaneous ones; at minima, they were lower by 4-6 ºC, and the length of the unfrozen period on Baikal decreased to 120-140 days. Given such conditions, water-associated migratory bird populations might well exist, and they could only be limited by the trophic factor. Thus, many sandpipers Charadrii (feeding on invertebrates), geese Anserinae (phytophagues), and Laridae (ichthyophagues) are excellently adapted to the contemporaneous tundra conditions, and it is sufficient for them to spend 2 or 3 months to breed their young population. Degtyarev (2000) arrived at the conclusion that populations of waterfowl and shorebirds could live in central Yakutia even during cooling periods. From a cave on the Dyuktai river (the right tributary of the Aldan), remains of Common Tern Sterna hirundo, Black-headed Gull Larus ridibundus, and Baikal Teal Anas formosa and several other typical duck species of the recent Yakutia were identified from late Pleistocene layers 14-12 thousand years ago; several remains are presumed to belong to extinct species of Anser and Mergellus (Mochanov, 1970, 1977, citation according to Panteleyev, 1999; Zelenkov, 2005). A survey of the paleontologiсal finds of birds from the Baikal region shows that they are dominated by representatives of genera of terrestrial and water birds which are typical of plain and mountain shrubs-steppe stations, as well as of rock biotopes (Panteleyev, 1999). During the quaternary period, the Baikal hollow was characterized by high seismic activity, which was causing fluctuations of the lake’s level with an amplitude in excess of 100 m (Yefimova, 2004). The outlet portions of the rivers (the Selenga in particular) changed their flow regime and configuration not only due to Baikal’s level changes but also directly under the action of tectonic events (Team…, 2004; Rezanov et al., 2004). Although Baikal’s deltas and shoals existed in the same areas over the course of hundreds of thousands of years, they were intermittently subjected to drastic changes. That has being affected to an equivalent degree the populations of waterbirds: the littoral rather than the deep-water pelagial of Baikal is highly important for them. Indeed, the noticeable changes in a biological production of the Baikal water ecosystem, registered by hydrobiologists (Mackay, 2007, and other pubications), should effect to the contents of waterbirds living at Baikal as well. As is intimated by the ornithofauna shaping in the Selenga delta (Fefelov et al., 2001), colonial species take from a few years to several tens of years to create a small nesting group. Given a favorable situation, a group is perhaps able to attain the rank of independent population for several hundreds of years. But even within such short time spans the birds had and have to change their nesting places around Baikal and in the Baikal region for the above- mentioned reasons. Most species must leave the region during cold periods, returning back at warm periods. Therefore, not only the formation of species but also the formation of subspecies was impossible here. The sole exception are the few species, having no direct links with water, predominantly sedentary and populating rock, tundra and mountain-steppe biotopes. They could evolve subspecies on account of mountainous isolates – a process that is widespread worldwide. However, the contemporaneous mountain ornithofauna is mainly composed by intruders from the north/north-east and from the south. The colonization of Baikal by migratory birds nesting in West or East Asia and hibernating in tropical latitudes, is limited by the lake’s geographic location. The shortest route between Baikal and wintering areas includes extensive high mountains and deserts of Central Asia that are unfavorable both for migration stops and for the shaping of new wintering places. As shown by the satellite tracking of Black Stork Ciconia nigra using satellite-borne radio transmitters (Bobek et al., 2004) and Imperial Eagle Aquila heliaca (Ueta & Ryabtsev, 2001), the birds wintering in South Asia, have to round the Central Asian region from east or from west during their migrations. Not all species are able to lengthen their flight route in view of shortage of time over a yearly life cycle (Zimin, 1988). This constrains the species composition of Baikal’s birds, at least nowadays. Populations of such birds as Common tern, Black-headed Gull, and many Anseriformes could exist almost constantly in the Baikal region in landscape-climatic conditions of the Pleistocene. Herring Gull Larus argentatus (sensu lato; in first line we mean a form mongolicus with uncertain taxonomic status), due to its behavioral adaptations and euryphagous character (Zubakin, 1988), could constantly inhabit Baikal. But this species prefers shore areas of productive water bodies and, perhaps, intermittently left the lake when it became ultraoligotrophic, and (or) with no shoals. Birds from grassy and tundra areas, such as sandpipers of the subfamily Calidridinae, and also mountain species, had to become ordinary during cold periods but disappear or form local mountain populations during climatic optima. On the contrary, the species of the more southern genesis, such as White-winged Tern Chlidonias leucopterus, and Marsh Sandpiper Tringa stagnatilis, could form during warming periods numerous temporary groups but disappeared at the onset of a cooling period. The species that preferred water bodies in later succession stages (like Eurasian Bittern Botaurus stellaris, and Pochard Aythya ferina), perhaps, populated the Baikal region at periods of mild and stable climate. The primary pathway for the shaping of the near-water ornithofauna of Baikal and of the Baikal region was, undoubtedly, by means of colonizations/recolonizations by birds from neighboring regions. Heterochronous climatic changes between areas of the two great lakes of Central Asia, Baikal and Hovsgol (Khubsugul) in Holocene (Prokopenko et al., 2007) also should be impacting to bird movements. The most impressive recent cases of range dynamics is a coming of Great Cormorant Phalacrocorax carbo back at Lake Baikal after its 40-year-long absence, and population dynamics of Asian Dowitcher Limnodromus semipalmatus. Until XX century Great Cormorant was very characteristic and abundant breeder at Baikal. In the middle XX century, the cormorant and Herring Gull fell in number depression, which seems to be induced by both human and natural factors together. Herring Gull as more adaptable species got increased in the last quarter of the century while the cormorant, specialized fish-eater, did not and then got wholly extinct at Baikal in 1960s. However, since 2004 it appeared in the West Mongolia and South Buryatia (Dorzhiyev, 2006) and since 2006 got nesting at Baikal again (Pyzhjanov, 2006), which may be induced by precipitation changes in Mongolia, especially in its eastern part. At now, its breeding number is going up to ca. 2 thousand individuals in the same two main areas of former abundance at Lake Baikal until mid-XX century. Mel'nikov (1998) has shown Asian Dowitcher, which main population is situated at steppe lakes of Central Asia, appears at Lake Baikal and around in very big number (to 5 thousand individuals, i.e. 20-30 % of its estimated world populaiton) during extremely droughts in the Central Asia like one in late 1970s. In other periods its number does not exceed few hundred individuals in the Baikal region. Many other charadriiform species seem to be varying their ranges with the similar scheme. Given the present knowledge of the spatial distribution of birds, the dynamicity of their habitat ranges, and their occurrence in conjunction with characteristic types of habitats, it can be suggested that in each subsequent interglacial period the species composition of the region’s birds differed from a previous interglacial period, as it was formed of innumerous components that managed to survive the cooling period and the new intruders. Also, biocenotic links were established anew. It would be justified in speaking of “extinctions” and rebirths of the ecosystems rather than of extinctions of the faunas. The occurrence frequency of landscape-climatic changes during the Pleistocene (especially in the late Pleistocene), perhaps, played a larger role than did their amplitude. The currently existing landscape- ecological complexes of birds have a combined, heterochronous origin. Thus the contemporaneous composition of Baikal’s ornithofauna had shaped itself mostly during the Holocene in accordance with changes in the landscape-climatic situation; however, because of the mountainous relief, the fauna of birds also includes species characteristic for the last glacier period. CONCLUSIONS

1. The composition of Baikal’s contemporaneous ornithofauna includes elements of a different geographic origin (with boreal and widespread species predominating). Endemic taxa were not observed in birds and in their parasites. A large number of meridional boundaries between populations of a single species or closely kindred species, primarily in water birds, bears witness to the stressed ecological conditions for the habitat of Baikal’s birds during the quaternary period. 2. Periodic colonization from neighboring regions should be recognized as the main avenue for the formation of Baikal’s ornithofauna. Only few palearctic bird species could populate Baikal throughout the entire Pleistocene-Holocene; most of the species had to leave the region at several periods because of unfavorable habitat conditions.

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