Научная статья на тему 'Adaptation of the Caucasian Black Grouse Lyrurus mlokosiewiczi to life in the high mountains'

Adaptation of the Caucasian Black Grouse Lyrurus mlokosiewiczi to life in the high mountains Текст научной статьи по специальности «Биологические науки»

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Аннотация научной статьи по биологическим наукам, автор научной работы — Potapov R. L.

Этот доклад был представлен мной на 6-м Международном симпозиуме по тетеревиным птицам в Удине, Италия, в 1993 году. К сожалению, рукопись доклада на английском языке не удалось вовремя подготовить, и было опубликовано только его резюме (Potapov 1995). Сообщение основано главным образом на материалах, опубликованных мною ранее на русском языке (Потапов 1978, 1985). Данный вариант представляет собой практически первоначальный текст доклада, в него добавлены лишь новые данные о последних палеонтологических находках тетеревиных птиц на Балканах (Boev 2002). Эти находки подкрепляют мою гипотезу о происхождении кавказского тетерева, предложенную ранее в упомянутых работах. Большее внимание уделено также значению высоких лётных качеств самцов кавказского тетерева (при крайней оседлости самок) для межпопуляци-онного обмена и поддержания единства вида.

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Текст научной работы на тему «Adaptation of the Caucasian Black Grouse Lyrurus mlokosiewiczi to life in the high mountains»

ISSN 0869-4362

Русский орнитологический журнал 2004, Том 13, Экспресс-выпуск 263: 507-525

Adaptation of the Caucasian Black Grouse Lyrurus mlokosiewiczi to life in the high mountains

R.L.Potapov

Zoological Institute, Russian Academy of Sciences, Universitetskaya nab. 1, St.-Petersburg, 199034, Russia

Received 12 April 2004

Introduction

This talk I presented at the 6th International Grouse Symposium in Udine, Italy, in 1993. Unfortunately, the manuscript of this talk was not ready in time and only abstract was published (Potapov 1995). Now, because of the courtesy of the Editor of the Russian Journal of Ornithology Dr. A. Bardin I received a good possibility to publish my manuscript in English in this journal. It is very important, because gives me the opportunity to publish not only manuscript and to add some new data about this species, but many other information edited before, in my monograph "Family Tetraonidae, Galliformes" (Potapov 1985) in Russian. This obstacle is forcing for some western ornithologists, who don't familiar with Russian language and think that it is enough reason to ignore Russian scientific sources, to reopen many details, that not only described in this monograph, but illustrated by pictures and graphics. Some of these ornithologists, who begin to visit many parts of the former USSR for ornithological research or bird watching, because of the same problems with Russian, re-opened a lot of usual things, that described in Russian ornithlological literature many times ago, over and over again, as a new data. Because of this, birdwatchers from abroad made a rough mistakes sometimes and published wrong information of such kind in scientific journals.

It is hard for me to forget, for example, how in the same symposium one of the birdwatchers (J.Pfeffer) tried to prove that he watched (and local hunters even collected for him) the ptarmigans Lagopus mutus in the Zerafshan Ridge in Northern Tadjikistan in 1993, at the distance more than 1600 km from the nearest habitats of this species. This region is not a white patch in ornithological map of the former USSR in any case. The birds of this mountains were studied carefully: by not less than 50 professional ornithologists (including myself) during last 160 years! Because of my appearance in dispute and convincing arguments that it is at least the rough error, the abstract of this talk was not included to the proceedings of Symposium, but this talk was published late in "Alauda" (Pfeffer 1997). And this wrong data is cited now as an established fact by some authors (Storch 2000).

The Caucasian Black Grouse Lyrurus mlokosiewizci is an unique species among all Old World Tetraonidae birds because of its living space, occupying only high mountains above the timber line (analogous in the New World is White-Tailed Ptarmigan Lagopus leucurus). There is a similarity of the Caucasian

Black Grouse with some southern populations of the Black Grouse Lyrurus tetrix in this respect: the later inhabits only the upper parts of the forest belt close to the timber line and adjacent part of the subalpine zone of the mountains (Straut-man 1954; Pauli 1974; Zettel 1974; Couturier 1980)). Moreover, this similarity shows the possible way of the origin of the Caucasian species of the genus Lyrurus (Potapov 1978).

Both species of this genus are similar in many features: the black general coloration with white patches of the males and its specific lire-shaped elongated tails, palearctic distribution, preference of the marginal habitats between woods and opens, the birch catkins as a main winter food, the same social structure of the leek and some others. In the base of this general features some special adaptations to life in high mountains were developed in Caucasian Black Grouse during its evolution.

Locomotion

The life of any bird species in the high mountains demands the corresponding adaptations to its specific conditions and first of all to locomotion in the vertically structured landscape. This is concerns both to the flight modes and to the walk ones. The last is especially important for the Galliform birds, that spend most of its time in the ground and must be adapted well to the pedestrian movements. It was shown (Potapov 1978, 1982) that the length of the legs of the Caucasian Black Grouse is the largest among all Tetraonid species and close to the same in some mountain Phasianidae species like Snowcocks Tetraogallus sp. (Table 1, Fig. 1).

Table 1. Comparative length of the hind limb in Black Grouses and Snowcocks (males)

in millimetres and % from the "Truncus"* (From: Potapov 1978, 1982)

The length of the hind limb bones Total length

Species Femur Tibiotarsus Tarsometatarsus of the hind limb

Mm % Mm % Mm % Mm %

Lyrurus tetrix 82.0 56.5 96.0 71.6 49.5 36.9 219.0 151.0

Lyrurus mloikosiewiczi 74.0 66.0 97.0 86.6 51.8 46.2 222.0 198.2 Tetraogallus himalayensis 107.7 73.2 145.8 98.0 76.6 52.1 330.1 223.3

* — "Main body size" — the length of the vertebra column from the front border of the 15-th neck's vertebra to the opening of the spinal cord's channel at the back part of the pelvis' surface.

The species from the last genera are more important to our comparison than other representatives of the Phasianidae family, because of its mode of walking. The snowcocks walk mainly up to the slope: if they need go downward, they use the flight. Caucasian Black Grouse have the same mode of the daily moving activity — upward on foot and down one by flight. The great length of foots is an adaptation to walk in the steep slopes with the numerous mounds and stones among the thick and tall grass and bush vegetation (Potapov 1978).

The wing of Caucasian Black Grouse differs from that of the Black Grouse. It is shorter, wider and has a more rounded top (Fig. 2, Table 2), especially in

Table 2. Dimensions of the wings in species of the genus Lyrurus (mm)

Species, subspesies Sex N Wing length The longest primary The length of the 2d secondary Wing width, % of its length The length of primaries, % of the longest one

Abs. % oftr. Abs. % of tr. 10th 9th 8th 7th 6th 5th 4th

Lyrurus tetrix Males 6 285 210 144.8 135 93.1 64.9 69.0 91.1 99.5 100.0 97.1 90.2 76.0

tetrix Females 7 235 — — — — 63.4 74.4 93.7 100.0 100.0 96.8 89.9 76.8

Lyrurus Males 2 211 152 135.4 130 116.5 76.0 65.0 86.7 94.2 100.0 100.0 97.5 90.4

mlokosiewiczi Females 7 197 — — — — 71.0 71.9 92.1 96.8 100.0 99.3 95.8 86.9

Note: the wing width was measured on the folded wing from manus bend to the apex of the 2d secondary.

Fig. 1. Comparative size of the bones of the hind limb (in the % from main body size). A — Lyrurus tetrix; B — Lyrurus mlokosiewiczi.

Fig. 2. Comparative size and shape of the male's wing (in the % from main body size). A — Lyrurus tetrix; B — Lyrurus mlokosiewiczi.

Fig. 3. Plan of the Caucasian Black Grouse male's gliding flight.

Solid lines — the gliding phases of the flight; vertical short lines — the wing beats;

A — ventral view; B — dorsal view; black spot — place of landing.

Fig. 4. The shape of the 10th primary of Lyrurus tetrix (A) and L. mlokosiewiczi (B). From: Potapov 1978.

the males. The width of the male's wing is greater because of the secondaries, the comparative length of which to the wing's length is significantly greater that in Black Grouse's ones (Table 2). These wings are adapted to the specific way of the male's flight. Males spend most of the time on the ground, and move mainly by foot, usually up slopes. When they need to move short distance to a place of feeding or resting, they use the normal horizontal flight, as do other tetraonid birds. Only if they need to move a long distance (to avoid the danger, to reach the place of the leek etc.) they use their specific downward flight, the main part of which is gliding (Potapov 1978).

This male's flight, described previously only in 1977 (Potapov, Pavlova 1977) and with a full description later (Potapov 1978, 1983, 1985), is unique among the representatives of the family Tetraonidae, but usual for many birds that dwell in high mountains. In this flight the birds use the force of gravity very effectively, and spend sufficiently less energy than in usual transporting flight, that was shown by me later (Potapov 2002).

The trajectory of this flight looks like a spiral descending parallel to a mountain slope approximately 100 m above it. The gliding phases of this flight occupy 75% of the flight time and are interrupted regularly, after every three to four seconds, by five to eight wing strokes (Fig. 3). It appears that the speed of the flight decreases during these strokes and direction of the flight becomes more horizontal. Moreover, this flight, so unusual for the tetraonid birds, is accompanied by a specific whistling sound, produced by the primaries of the spreading wings during the gliding phase. (It is wonderful that this prominent feature of this flight, was mentioned for the first time only in 1942 (Laister, Sosnin 1942): the authors described the flight of the males after the end of the autumn moult and mentioned that this sound was absent in moulting birds.)

This prolonged sound regularly interrupted by several (five to eight) short whistles at the moments of the wing strokes. These are the same short whistling sounds produced by male's wings during flutter jumps in the courtship displays (it will be discussed later). The sounds of this flight were recorded later by German ornithologists in Teberda State Reserve in 1989 (Bergmann et al. 1991).

The structure of the wing primaries shows that all these sounds are produced by outer primaries, especially the outermost one (№ 10, Fig. 4). This feather in Caucasian Black Grouse male is shorter and narrower than in Black Grouse male, and has no broadening at its base, which is so usual for galliform birds. It is interesting to note, that it is an evidence about the absence of this whistling sound during the male's flight at the time of the intensive moult (Laister, Sosnin 1942). I am sure that this absence of the whistling sound occurs at the time when the outer primaries are changed during the moult.

Another important feature of these primaries is the strong wear of the inner web's margin, especially in the five outer primaries, mentioned by myself for the first time after careful investigation of the collection specimens in Zoological Institute of the Russian Academy of Sciences (Fig. 5; Potapov 1978, Fig. II, photo

Fig. 5. The outer edge of the male's 10th primary in the spring.

A — Lyrurus tetrix, B — L. mlokosiewiczi (from: Potapov 1978, fig. II, fhoto-supplement).

supplement). First of all, this wear is a result of strong air pressure to the feathers during the gliding flight. The wing of one year old males is not different from the adult's one, but the primaries in the female's wing do not any sign of wear. The ilight of the female is of the same type as in the Black grouse Lyrurus tetrix (males and females) , i.e. it is usual bearing (horisontal) flight in which a series of flaps alternate with short gliding on spread wings. Females of the Caucasian Black Grouse use flight rarely, only flying short distances. Unlike males, they have never been observed in downward flight. This kind of sexual dimorphism in flight is only one observed among the Tetraonidae species (but may be exists in Siberian Spruse Grouse Falcipennis falcipennis).

In general, the flying ability of the Caucasian Black Grouse male is very impressive, especially if somebody observes the bird descending to the slope, as it seems, from heaven, resembling more a falcon than a grouse. This flying ability permits the subadult and adult males to fulfill the long distance flights to reach new favourable spots that was occupied by other populations. In the case of subadult males this process is usual dispersion, but in the case of adults we see another processes in the populations life. To study these adult dispersions, special radio-tracking technology needs to be used. The movements of the males help understand why this species is monotypic, despite the fact that the species populates entirely different areas with different natural conditions. This is especially important in the case of the populations of the Great and Minor Caucasus mountains, which are largely seperated. The males accomplish a genetic exchange between the different populations can do this because of its' high flying ability (Potapov 1985).

By the way, all species of Snowcocks Tetraogallus sp., both males and females, that possess extremely specialized downward gliding flight, have lost the ability to fly horizontally (Potapov 1966, 1992), have normal margins of the outer primaries' inner webs, without traces of any wear. Only the upper parts of the inner webs of inner primaries M« 5-8 have worn out margins. The pressure on the snowcock's wing is much more than on the Caucasian Black Grouse's wing. The body mass alone gives a pressure of 1.7-2.3 g/sm2 on the open wing (Potapov 1992) and is significantly higher during the gliding flight at a speed of about

B

Fig. 6. The shape of the outer retrices of the Lyrurus mlokosiewiczi adult male. A — general view; B — cross-section close to the end of the tail.

Fig. 7. The position of the adult male's retrices and alula at the moment of the steep turn in the upper point of the flutter jump (from: Potapov 1978, 1985).

90 km/h. It means that the snowcock's wing is more adapted to the gliding flight than the wing of the Caucasian Black Grouse, which is multifunctional and adapted to the different types of flight.

The tail of the adult males of Caucasian Black Grouse is similar with Black cock's one in shape (lire-form with elongate outer retrices) but differs in many details. First of all the tail of Caucasian species is more long (relatively to the "truncus" 198.2%, instead of 151% in L. tetrix) and the length difference between central (shortest) and outer (longest) retrices is twice less (Potapov 1985). But the main difference between this two species is in the shape of the elongated outer retrices. In L. tetrix the outer feathers are widen to the top and the top is curved outside: both webs, inner and outer are situated in the same flatness (Fig. 6, a). In L. mlokosiewiczi the inner and outer webs situated under the angle near 90° and the feather remember the gutter. The outer elongated feathers in male's normal state are put in one another so that every half of the elongated tail looks like a gutter and fulfill the functions of the gutter (Fig. 6, b). The functional significance of this shape is obvious. Main habitats of the adult males from spring till autumn are the alpine and subalpine meadows with tall grasses. During the rainy weather (that is usual in these altitudes) the grass became wet. The males keep its tails parallel to the ground during feeding and walking and the tail feathers may become wet quickly, but its gutter's shape help to remove the water.

Another function of the long tail is to be the mark during courtship displays. The location of one or another male in the leek is possible sometimes only due to the raised long tail that is visible among the tall grass. The role of the long male's tail to manoeuvre ability of the flight is doubtful: during the sharp turns the long soft tail feathers curves easily because of the pressure of the air (Fig. 7).

The leek and courtship display

The mating system in Caucasian Black Grouse is the same as in Black Grouse. During the mating season (from middle April up to middle May) the males gather together in special traditional places — leeks, where every male have its individual territory that it defends from the neighbours and where it performs nuptial rituals. These gatherings are visited by females and every hen select the partner for mating that take place in the selected male's territory.

This general picture, very similar with that of the Black Grouse's mating system, differs nevertheless in many important details. First of all, the leek of Caucasian Black Grouse is mute. All males fulfill its rituals in silence, without any vocalization. Only during the confrontations and very rare, the males can utter the low guttural grumbling that can be hear at the distance not more than several meters (Averin 1938). It is interesting to note, that such grumbling is very similar with that utters the Capercaillie x Black Grouse bastard in the same situation (Potapov 1978). This absence of vocalization I explained by the specific high mountain conditions: the great distances between steep slopes above the timber line, constant strong winds make the vocal signals less effective than visible ones. The leeks of this Black grouse are situated (as a rule) in the open steep slopes above the trees-bushes vegetation and the black males are distinctly visible in the light-yellow old grass' background at the long distances (Potapov 1978). The reduction of the syrinx in males of the Caucasian Black Grouse (Fig. 8) is the evidence of the long term evolution of this species in the high mountain conditions.

The main element in the male's courtship display of this species is the flutter jump, described in details only recently (Fig. 9, Potapov, Pavlova 1977) and re-

peated with some additional details later (Vitovich 1986). It fulfills, as a rule, in the steep slope and from the specific start posture. The bird is sitting with its back toward the slope, with slightly elevated and protruding breast. Before the start male stands up in vertical position and jump up with 4-5 strong wing beats (the same number of wing beats mentioned Vitovich 1986, but sonogram of this flutter jump shows 7-8 ones — Bergmann et al. 1991). The bird makes 180° turn to the left or right sides in the upper point of this flatter jump, which is no more than 2 m high and lands passively, with the half-folded wings and with the head towards the slope (Fig. 10). Sometimes this flutter jump performs without the turn (in flat surface — Vitovich 1986). Such performances repeat again and again and its frequencies reflect the level of the sexual excitation (Averin 1938). The main significance of this flatter jump is to attract female's attention by the specific whistling sounds, produced by outer primaries during the flaps and audible to the distance up to 150 m, and by demonstration of white parts of the lower surface of the wings (Potapov, Pavlova 1977). Because of the turn during this flight these contrast white patches of this black-colored bird are clearly visible for all surrounding males and females in both sides and below from the lecking male, even in the darkness of the early daybreak (Fig. 10). The second functional significance of the turn during flutter-jump is to land by the suitable way in the opposite direction from the start, with the head directed to the slope.

Sometimes the male fulfill the flutter jump without turn, that was happen when the performance take place in more or less flat surface (Vitovich 1986). In all other tetraonid species the flatter jump with turn have only Falcipennis falcipennis, but significance of it in this case is unclear. May A tzk B

be, it was made because of the little size of the ig^J

clearings among the thick forest, where the males ^^ ^^ of this species perform its nuptial displays in soli- Fjg 8 Syrinx of the Lyrurus tetrix tude. I watched the male of this species which (A) and Lyrurus mlokosiewiczi (B). fulfilled this flutter jump without the turn (Potapov 1969). In any way we may to point that the leek of Caucasian Black Grouse, during it's culminating phase in the deep twilight, when the mating is took place, is hardly detected as to the conspecific birds as to raptors. And because of such circumstances it is easy to evaluate the significance of stability of the leek grounds. All explorers who studied the breeding process of this species stated that they didn't know any case when these birds changed the place of the leek ground (Averin 1939; Vitovich 1986). In any case no of them never fixed the appearance of the new leek ground, but only the disappearance of some of them because of the constant decrease of bird's populations. In comparison with this species, males of L. tetrix have no problems with the advertising females after the change of the place of leek ground and even when the male performs its displays alone: the loud nuptial song audible at distances more than 1 km easily attract females if they present in surroundings. There is a good analogue of such stability of leek

Fig. 9. The first plan of the flutter jump of the Lyrurus mlokosiewiczi published in literature (Potapov, Pavlova 1977). All drawings are made from photos. The position of the male in the upper point — from: Potapov 1978.

grounds in the case with the Capercaillie Tetrao urogallus and because of the same reasons. But in the last case this stability expresses in less degree (many cases of the appearance of new leek grounds are known), mainly because of the constant processes of successions in forest communities.

The leeks of the Caucasian Black Grouse are hard to find only in the twilight hours, when the mating (the main event of the leek process) occurs. In the daylight the leek ground and the males are clearly visible. At this time, the leek is exploited by raptors, mainly by birds of prey. For example, the Golden Eagle Aquila chrysaetos in the North Caucasus hunts for males in leeks regularly, but males usually avoid its attacks hiding in the nearest shelter (bush or rock) or by jumping up when the eagle approaches. The eagle's attack is usually unsuccessful because of this (Vitovich 1986). This interesting behavior of males means they have good experience in such situations.

standing crest (from: Potapov 1978, 1982).

A significant morphological character of the males of the Caucasian Black Grouse is the female-like coloration of one-year old males. It is necessary to emphasize that it is the only species in the family Tetraonidae that has a distinct difference between the one-year old male coloration (mainly gray-brown, similar with that of the females), and the older generations' one (entirely black). The coloration of the one-year old male of the Black Grouse L. tetrix, for example, is nearly the same as in older ones except for some minor details. The young males of both species participate actively in nuptial performances in the leek grounds, with the same subdominant status, in the same positions on the margins of the leek ground, and with the same negative results in their attempts to mate.

The sharp difference between the first and subsequent coloration of adult males in L. mlokosiewiczi is always present and is undoubtedly maintained by natural selection. Sometimes one-year-old individuals with single black feathers

are found in the collections (Potapov 1985, Fig. 151, 2). We think that this trait could have been more expressed if it was not suppressed by natural selection, which supports the gray female-like coloration over the black feathered coloration. At the moment it is difficult to explain this, because information on the ecology of the Caucasian Black Grouse, and especially about its winter life, is insufficient. It is interesting to note, that in this species females spend the winter in the upper part of the forest belt in flocks, together with one-year-old males. They all have the gray coloration and even experienced ornithologist have problems in distinguishing young males from females in the same flock from a distance. At the same time the old males with their full black color spend the winter in separate flocks mainly above the timberline (Vitovich 1986). In L. tetrix and both species of Tetrao the young males spend the winter together with old males, not with the females, or in the mixed flocks. It is possible, that the gray coloration of one-year-old males of L. mlokosiewiczi is somehow connected with the fact that they spend their first winter together with females. Another possible explanation is that the gray cryptic coloration of the young males helps them to escape raptor's attacks in the leeks because the young males do not yet have the experience to avoid the attacks. I thinks that in any way this specific character of the Caucasian Black Grouse is connected with the specific natural conditions in highlands, where the cryptic coloration of one-year-old non-experienced males give them more chance to survive.

Another specific morphological character of the Caucasian Black Grouse male, which is closely connected with courtship display s, is the structure of the specific "eyebrows" (Fig. 11). In all the species of the family Tetraonidae the males have the eyebrows — naked stripes of skin above the eyes, covered by a complicated mosaic of knobs and protuberances, rich of blood vessels. Because of this the color of the "eyebrows" is usually red. Through the whole year, the "eye brows" are moderate in size and are partly covered by feathers. During the breeding time they grow significantly and become bright red, due to the expansion of the blood vessels. The females have these "eye brows" too, but much smaller and non active during the mating season. The "eyebrows" in Tetraonidae species are of 2 types: The first is flat, covered by low knobs and with the high crest along the upper margin of the "eyebrow". In calm condition the crest is hanging down and covering the "eyebrow". The "eyebrows" of the second type are convex, with high knobs, tubercles and protuberances. The second type is found in species of the genera Bonasa, Falcipennis, Tetrao, Dendragapus, the first — in genera Lagopus, Tympanuchus, Centrocercus (Potapov 1985). The genus Lyrurus is unique in this respect: one of the two species of this genus, L. tetrix has the "eye brow' of the second type, while another species, L. mlokosiewizci — of the first type (Potapov 1978, Fig. 4; 1985, Fig.28). The first type seems to be more adaptive from the bioenergetic point of view. During no-breeding seasons, especially in winters, this naked eyebrow decreases in size and in addition, folds in two (the marginal crest lays over flat surface of the eyebrow). In this position it is covered by the nearest feathers practically completely, as in ptarmigans, hidden from frozen air and preventing the heat losses.

This structure of the eyebrows of the Caucasian Black Grouse which is similar to the Ptarmigan's one, may be considered as a plesiomorphic character and an

evidence of a close relationship of the ancestors of genera Lyrurus and Lagopus (Potapov 1978). It is possible that L. mlokosiewiczi maintained the ancestor's type of eyebrow because of the more severe climate in the subalpine and alpine belts of the high mountains than in the plains, especially during the cold epochs of the Pleistocene.

The origin of the Caucasian Black Grouse and its range

In order to understand the origin of this grouse and its range, we have to answer two questions: who was the ancestor of this species and how had it evolved to its modern state. It is easier to answer the second question, as it is simpler and is based mainly on comparisons and logic.

First of all, the origin of the Caucasian Black Grouse from an ancestor common to it and the Black Grouse is obvious to all taxonomists, because both species are similar morphologically and occupy similar habitats. Modern Black Grouses live in semi-exposed habitats along the southern borders of the Pa-laearctic forest zone, and in the plain forest-steppe zone. In high mountains, both species prefer the same border zone between open and closed habitats along the timberline. In some places like Carpathians or Altai mountains, plain and mountain populations of Black Grouse are completely separated by the well developed forest belt. In the southernmost parts of the range, Black Grouse dwells only in mountains along the timberline (Alps, Balkan Mts.), because the climatic conditions below the forest belt are unsuitable for tetraonid birds in general (e.g., in southern Balkans) and because of anthropogenic extermination (e.g., in the northern surroundings of the Alps). It is noteworthy that in northern Caucasus, plain populations of L. tetrix were separated from high mountain populations of L. mlokosiewiczi by a distance of 120-150 km no less than 100 years ago. This space is currently occupied by a thick and rich mountain forest, unsuitable for both species (L. tetrix and L. mlokosiewiczi)', in this case the forest separated two species (Menzbier 1902; Potapov 1985).

At present, no paleontological data about the ancestor of the Caucasian Black Grouse is available. However, we have a reason to believe, that its ancestor was a mountain bird. If so, it could reach the Caucasus only from the Balkan Mts., via the mountain ridges of Anatolia. The distance between the nearest populations of Caucasian Black Grouse and the mountain populations of the Black Grouse in the Balkans (Greece) is now about 1500 km. There are many mountain ridges that form a virtually uninterrupted chain between Balkans and Caucasus. At present, however, environmental conditions in this area are unsuitable for the Caucasian Black Grouse, mainly owing to the dry climate and consequently, the absence of the forest belt and Rhododendron and Juniperus bushes in the sub-alpine zone. During the cold epoch of Pleistocene, the natural conditions in this region were probably quite different. It is well known that the great climatic changes during the Pleistocene strongly influenced vegetation in the southern mountains of the Palaearctic. In these mountains, forests appeared and disappeared, and theis size fluctuated. Sometimes, the forest belt only moved up or down the slope, changing its altitude above sea level. The Pleistocene populations of ancient Black Grouse in mountains and plains parted at times, and joined again, in accordance with the appearance and the disappearance of the forest belt. One

can assume that during one of the cold epochs the ancestral Caucasian Black Grouse population that dwelled around the timberline in the mountains of the Balkan Peninsula got a possibility to expand eastwards along the mountain ridges of the Lesser Asian peninsula, up to the Caucasian Mts. It is the only possible scenario if the hypothesis on the origin of the Caucasian Black Grouse from the mountain ancestor is accepted. This could happen long before the middle Pleistocene, because the earliest fossil remains of this species from Caucasian caves are dated by 350 KA, i.e. by the beginning of the Rissian glaciation (Potapov 1985), oxygen isotope stage 10. No data about the paleo-environment situation during the Pleistocene in the mountains of the Northern Turkey is yet available, but pollen analyses show that even 10000 years ago the upper birch-forest belt was well-developed in the mountain forests in the north-west Turkey (Keroglu-Dag) (Zeist, Bottema 1991). This habitat, which is so important for the Caucasian Black grouse, is now absent there. We have all the reasons to assume that such a habitat did exist in most of the northern Anatolian Mts. during the cold epochs of the Pleistocene, starting from the first one (Gunz).

Later, the natural conditions in the Balkan Mts., that were suitable for the Caucasian Black Grouses' ancestors, disappeared during one of the warm periods of the interglacial times. The ancestors disappeared too. This is not surprising, if you take into account the relatively low altitude of these mountains. As a result, the Caucasian Black Grouse survived till the present time only in the large area of high mountains — in the Caucasus Mts. and the adjacent mountain ridges.

The arrival of the ancestral form of the Caucasian Black Grouse to the Caucasus from the northern plains is less likely than the previous scenario. In this case, we must accept the origin of this species as from the lowland ancestral population. The ancestors of this species must have reached the Caucasus through the open steppe lowlands at the time no later than the Mindel-Riss interglacial period. There is one problem — there is no data about the animal life and vegetation in this area during the first half of the Pleistocene period. It is only known that in the interglacial periods, large scale transgressions took place and the water covered the territory between the Black and Caspian seas north from Caucasian Mts. Such transgressions interrupted any connections between the faunas of the European steppe zone and the Caucasian Mts. In any case it is hard to believe that a lowland species could have evolved to the highly specialized Caucasian Black Grouse during the comparatively short duration of the time from the Gunz glacial epoch till the beginning of the Rissian glaciation (nearly 500 thousand years). Nevertheless, we cannot completely deny the possibility of such events despite the full absence of the Tetraonid fossil remains in the vast territories of plains in southern parts of Ukraine and Russia up to the Wurmian time. It is very curious that only during, but not before, the Wurm glaciation the Black Grouse and the Ptarmigan Lagopus mutus reached the mountains in Crimea. Judging from the size of the fossil bones, these mountains were inhabited by Lyrurus tetrix, which was smaller in body size than the recent populations (Potapov 1985). This species may have reached the Crimea Mts. during one of the interglacial periods during the Wurm glaciation, when the arboreal vegetation appeared in the modern steppe zone, especially along river valleys. It may have happened, for example, during the Mikulinsk's interglaciation 170-150 thousand years ago, meaning a long time after the appearance of the Caucasian Black Grouse in the Caucasus.

The Black Grouse reached up to the foothills of the Caucasian Mts. during the wet periods of the Holocene, perhaps during the humid Atlantic period (about 5-6 thousands years ago), when there was arboreal vegetation along the river valleys. During this invasion the Black Grouse reached not only the northern shore of the Black Sea, but even the northern margins of the large forests, that covered the northern foothills of the Caucasian Mts. They could not however spread out further into the mountains (see before).

On contrary to the southern steppe zone in Ukraine and Russia, in the mountains and foothills of the Balkan Peninsula there are a lot of finds of fossil tetraonid birds as far as the Pliocene period (Janossy 1974, 1975; Bochensky 1991; Boev 1999, 2002). There are several finds of ancient forms here that have some specific features of the genus Lyrurus. One of them was described as fossil species Lyrurus partium (Kretzoi, 1962), that existed for the first half of the Pleistocene and was distributed from France to Ukraine. An assumption was made that this species was the direct ancestor of L. tetrix, which appeared after the disappearance of the L. partium (Janossy 1975). Now, new data has been obtained that opposes this opinion: it seems that both species overlapped in time and, moreover, were found in the same place, in the same time (Boev 2002). This means that both species originated from one ancestor. We can assume that this ancestor for both species was also the ancestor for the Caucasian Black Grouse. Many fossil remains of the Black Grouses that were found in southern Europe, including the Balkans, were described as L. cf. tetrix, L. aff. partium, and L. cf. partium. Some bones had a transitional features between the genera Lyrurus and Lagopus, and between Lyrurus and Tetrao. Possibly, this is the evidence indicating at the common ancestors of the recent genera mentioned above, before they were separated completely and evolved into different genera. The general picture of initial differentiation of the grouse is still unclear, especially considering that most of the pa-leoornithologists believe that the Black Grouse and the Capercaillies belong to the same genus, the genus Tetrao (Boev 2002; Bochensky 1991, etc.). The authors that cannot find the differences between the modern genera that differ so clearly (for example, the genera Tetrao and Lyrurus), have even more difficulties distinguishing fossil remains of these genera. Still, there is a very good possibility finding the remains of the Caucasian Black Grouse's ancestor in the Balkan mountain area in the later Pliocene — early Pleistocene lawyers , i.e. at the time when the global cooling began. In accordance with this, the adaptive radiation of the tetraonid's ancestors, started earlier in the North-East of Eurasia (in the so named Beringia — Potapov 1968, 1970) was accelerated significantly.

The L. mlokosiewiczi, when compared with L. tetrix, has some specific features, shown as a deep adaptation to highland natural conditions, as the preservation of some ancestral peculiarities. This is an usual situation in the process of the mosaic evolution under constant natural conditions. The highland's natural conditions forced Caucasian Black Grouse to develop useful changes in the body's proportions, wing shape, color of old and one-year-old males, the form of the tail feathers, etc. In the same time, the stability of the mountain environments (most important the climate) was favorable for the preservation of many ancestral features in the morphology, ecology and behavior of the Caucasian Black Grouse. The approximate stability of the climate in the high mountains is conditioned by

the effect of the height above sea level. Every vegetation belt in the mountains can conserve its climatic optimum by the change of the height above the sea level — it can to move lower during the cold epochs and higher during the warm ones (Potapov 1978). This rule is clearly right for all high mountain dwellers, plants and animals alike. The richness of the endemic species, both of plants and animals, is a well known peculiarity of the high mountain systems like the Himalayas or the South American Andes.

The study of the origin of L. mlokosie-wiczi is closely connected with the problem of the origin of the genus Lyrurus as a whole. The doubtless monophyletic origin of the family Tetraonidae means that in the first stage of the adaptive radiation of the family's ancestor the ancestors of the following genera must have appeared. In that stage the existence of the fossil taxa that are transitional between the closely related genera was quite a natural phenomenon. The presence of some similar features in the morphology and ecology in the genera Lyrurus and Lagopus is evidence of a more close relationship between them, than between Lyrurus and Tetrao (Potapov 1978, 1985). Besides the construction of the eye brow, mentioned above, there are some other morphological resemblances. One of them is the shape of the tail, so specific in the genus Lyrurus, where the central retrices are shortened significantly. There is an analogy of this in Lagopus lagopus. In some cases, both of males and females, especially in the northern populations there is some shortening of the central, and sometimes of the outer, retrices. Because of this the tail of these specimens has a shape very similar to that of the females of both species of Lyrurus, especially L. mlokosiewi-czi (fig. 12). The reason of such shortening of the central retrices in Lagopus lagopus is the late molt, when the central tail feathers, that grow last, have no time to reach normal length before the beginning of winter. The lyre-shaped tail in Black Grouse males might develop from this starting position because of sexual selection. This shape of the tail increases the impression of the male's body size during courtship displays, when the tail stands vertically and opens (in the case of Lirurus tetrix), or it shows the location of the male in tall grass, as in the case of L. mlokosiewiczi. Another important similarity between Lagopus and Lyrurus is the preference of the open habitats — borders of forests, forest-steppe in

Fig. 12. The shape of the female's tail in Lagopus lagopus (A — normal, B, C — aberrant), Lyrurus tetrix (D) and L. mlokosiewiczi (E). (From: Potapov 1978, 1982)

the case of the Black Grouses, or the open tundra with or without bushes and forest-steppe in the case of the Willow Grouse and the Ptarmigan. In the mountains the representatives of both genera dwell in subalpine and alpine belts, sometimes close to the timberline.

A possible confirmation of my hypothesis about the close relationship between these two genera are the finds of fossil bones in the Balkans (Bulgaria) from Villafranchian (more than 1.5 million years ago) up to the Wurmian period (70000 years ago) that have the transitional characteristics of the Lagopus and Lyrurus species (Boev 2002).

Conclusion

The Caucasian Black Grouse Lyrurus mlokosiewiczi (Tacz., 1875), is the only species among the tetraonid birds that has deeply adapted to life in the high mountains. It is a true high mountain bird. Its distributional area, isolated from the main distribution of the family Tetraonidae, coincides completely with the specific high mountain area of the Caucasus and the adjacent territories. This is an evidence of a very ancient age of the species, what is a relic indeed. Most of special features of the morphology of this species are the adaptations to life in high mountains (long legs and shorter rounded wings, the elongated male's tail with the gutter-like feathers, the female-like gray coloration of the one-year-old males), as well as the special features of his ethology (specific male's gliding flight, unusual for the tetraonid species and usual for many high mountain birds; and the absence of nuptial vocalisation). The high flying ability of the males are giving them the possibility to fulfill the genetic connection between isolated populations of this species and to support its morphological unity. The unique structure of the male's eyebrows is, however, the plesiomorphic feature, that draw the lineage of the genus Lyrurus with that of the genus Lagopus.

The origin of the Caucasian Black Grouse from the mountain populations of one of the ancestors of the genus Lyrurus is the most probable. The ancestors of this species could reach the Caucasian Mts. only from the west, from the mountain areas of the Balkan Peninsula in which many finds of ancient tetraonid species were made. The distribution of L. mlokosiewiczi from the Balkans to the Caucasus was possible only through the mountain ridges of Asia Minor, where natural conditions were suitable for this species in the cold epochs of the Pleistocene.

We can only approximate the time of the origin of the Caucasian Black Grouse. The earliest finds of the fossils belonging to this species are dated as 350 KA (oxygen isotope stage 10 — the beginning of the Riss Glaciation). So, the appearance of the ancestor form of this species was possible up to the first glaciation of the Pleistocene, i.e. the Gunz period, nearly one million years ago.

At the end it is necessary to point out that this article is the manuscript of my talk, made in 6th International Grouse Sympoxxxxsium in Udine, Italy, in 1993 (with a few additions) that was based on my own data, published in 1977, 1978, 1982 and 1985.

The author is very grateful to Nick Potapov for his genuine efforts in lingustic improvements of the English text, and to EA.Pavlova for her important help in preparing illustrations.

References

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Адаптация кавказского тетерева Lyrurus mlokosiewiczi

к жизни в высокогорье

Р.Л.Потапов

Этот доклад был представлен мной на 6-м Международном симпозиуме по тетеревиным птицам в Удине, Италия, в 1993 году. К сожалению, рукопись доклада на английском языке не удалось вовремя подготовить, и было опубликовано только его резюме (Potapov 1995). Сообщение основано главным образом на материалах, опубликованных мною ранее на русском языке (Потапов 1978, 1985). Данный вариант представляет собой практически первоначальный текст доклада, в него добавлены лишь новые данные о последних палеонтологических находках тетеревиных птиц на Балканах (Boev 2002). Эти находки подкрепляют мою гипотезу о происхождении кавказского тетерева, предложенную ранее в упомянутых работах. Большее внимание уделено также значению высоких лётных качеств самцов кавказского тетерева (при крайней оседлости самок) для межпопуляци-онного обмена и поддержания единства вида.

Ю GS

ISSN 0869-4362

Русский орнитологический журнал 2004, Том 13, Экспресс-выпуск 263: 525-536

Периодизация постэмбрионального развития птиц

А.С.Родимцев

Кафедра биологии и биоэкологии, Международный независимый эколого-политологический университет, Красноказарменная ул., 14, Москва, 111250, Россия

Поступила в редакцию 27 мая 2004

Индивидуальное развитие организмов состоит из ряда последовательных периодов, в течение которых они претерпевают количественные и качественные изменения, а также находятся в определенных отношениях с окружающей средой. Периодизации онтогенеза позвоночных животных посвящена обширная литература, имеющая солидную историю и охватывающая эмбрио- и постэмбриогенез представителей разных классов. В основу периодизации разными авторами кладутся морфологические, физиологические и этологические критерии.

Целью данной работы является анализ состояния изученности периодизации постэмбриогенеза птиц. На основе литературных данных и собственных материалов автора обосновывается выделение периодов в пост-натальном онтогенезе полуптенцовых и птенцовых видов. Нами были ис-

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