ISSN 1995-4255, Contemporary Problems of Ecology, 2008, Vol. 1, No. 2, pp. 227–237. © Pleiades Publishing, Ltd., 2008. Original Russian Text © V.N. Ryzhanovskii, 2005, published in Sibirskii Ekologicheskii Zhurnal, 2005, Vol. 12, No. 3, pp. 475–487.
Dates and Duration of the Basic Seasonal Phenomena in the Annual Life Cycle of Passerines of the Subarctic Zone on the Example of the Lower Ob’ Region V. N. Ryzhanovskii Institute of Ecology of Plants and Animals, Uralian Branch of the Russian Academy of Sciences, ul. Vos’mogo Marta 202, Yekaterinburg, 620144 Russia Abstract—On the basis of a long-term study of passerines in the Lower Ob’ region, data were obtained on the beginning and duration of arrival and flying away, reproduction periods, and post-breeding and post-juvenile molting. The triggering factors are discussed in this paper. DOI: 10.1134/S1995425508020094
INTRODUCTION The main limiting factor for the migratory passerine birds to stay in the subarctic zone is the duration of the above-zero temperature period. Its average duration at the latitude of Salekhard (Lower Ob’ region, 66.5° N) is 94 days, and at the latitude of Tambei Village (North Yamal, 71° N) it is 51 days [1]. A simple summing of time necessary for northern passerines to preempt territories, form couples, nest, molt, prepare for migration demonstrates its deficit in forest-tundra and even more so in the tundra zone. Deficiency in the warm season for successful breeding of birds already in the northern taiga zone has been the focus of attention for the Karelian ornithologists. They also determined the set of adaptations directed at the minimization of the stay duration for the north-taiga birds in their nesting places [2]. For the subarctic zone the issue was addressed by Danilov [3], who noted that the specific seasonal conditions make an impact on all aspects of the birds’ life and should serve as a selection factor for forming the high-latitude avifauna. In succeeding years the works dedicated to certain seasonal phenomena of the annual cycle of the birds of the Lower Ob’ region and Yamal Peninsula were published [4–7]. The sum of consequent events of certain times and durations — from the arrival of the first birds to the departure of the last ones — has never been studied. There are no studies in the rest of the subarctic zone. The given work fills the gap for passerines of the Lower Ob’ region. MATERIALS AND METHODS The paper is based on the materials collected in the Lower Ob’ region and in the Subarctic Urals in 1971–1990. The observations of 1971–1975 and 1984 were conducted on the territory of the forest-tundra station “Kharp” of the IBP, 13 km from Labytnangi. In 1976–1977 we worked in the Subarctic Urals in the Sob’ River valley, 60 km from Labytnangi; in other 227
years — in the valley of the Ob’ River near the village of Oktyabr’skii, 5 km from Labytnangi. All stations of the material collection are located roughly at the latitude of the Arctic Circle. There are the year-round observation data on the birds encountered in these regions; information on the dynamics of bird catching in 1976–1990 (more than 19 thousand individuals of Passerines); the results of the daily counts of passerines over a test area (22 hectares) in the Ob’ flood forest in 1979–1983 during arrival and formation of the local populations; data on the nests (more than 1500 cards of nests). Molting was studied both in the nature for the birds caught by nets and traps and those kept in cages. The plumage state of the once and repeatedly caught birds was described using the method by G. A. Noskov and T. A. Rymkevich [8] (more than 5000 descriptions). The birds caught in spring (more than 200 individuals of 12 species) and the birds fed since 10–14 days of age (more than 400 individuals of 25 species) were kept in cages. Determining the dates. Until 1976 the terms of arrival were determined during routes and excursions, and from records made at the observation points. In succeeding years the basic dates of the beginning of arrival and duration for the majority of the species of passerines of the Lower Ob’ region were obtained with the help of nets and traps. In 1976–1978 birds were caught only with mist nets of the total length varying from 40 to 230 m. Since 1979, in addition to the nets, a “fisher” trap was set on the bank of the Ob’ River, 80 m long, 25 m wide at its mouth, and 8 m high. In the first half of summer the trap faced southward and from mid-July — northward. To determine the date of the beginning of egg-laying, the nest cards were selected, which had the dates of the beginning or end of egg-laying, or hatching of the first chick. In the latter case the date of the beginning of egg-laying was determined from the average duration of incubation. The duration of incubation and feeding was determined using the nests that were under
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control from the first egg to the last hatchling. The egg-laying season is the period from the appearance of the first egg in the earliest nest to the laying of the last egg in the latest of the controlled nests. The nesting season is the period from the first laid egg in the earliest nest to the last hatchling leaving the latest of the nests. Analysis of molting requires dividing the process into a number of stages. The post-breeding molting of all species except Arctic warbler (Phylloscopus borealis Blas.) was divided into 11 stages [9]; for Arctic warbler it was divided into 6 stages [10]. Post-juvenal molting was divided into 5–7 stages depending on the number of the replaced feathers [6]. The figures that characterize the molt are different from those of the nesting. The columns “Dates of the beginning of postbreeding and post-juvenile molting” gives the periods of the molting entry (numerator) and the average dates of the beginning of molting (denominator). It also shows the average duration of an individual’s molting (numerator) and the duration of the molting season, i.e. the duration of the period when the molting birds of a given species are met in the controlled area (denominator). The climate conditions in 1971–1990. In the Lower Ob’ region the dates when snow begins to intensively melt and disappears from the nesting biotopes and daytime temperatures exceed zero vary from year to year. The Arctic proximity is evident when sometimes winter comes back in May–beginning of June. The Ob’ River seriously influences the spring weather in the study area. After ice drift, with masses of warm water entering the floodplains, the colds return for very short periods of time and snowfalls are replaced by rains. In the Ob’ valley the beginning of the arrival of the majority of passerines coincides with the ice drift or happens somewhat later. The egg-laying period begins only after the ice drift with all birds but hooded crow (Corvus cornix L.) and European magpie (Pica pica L.) which do it before. For 20 years two late-spring (1972 and 1978) and two early-spring (1977 and 1982) years were registered. In May of 1972 there were several relatively warm days at the end of the second ten-day period, which resulted in snow melting on the roads. The intensive warming began on June 4–5, the ice drift on the Ob’ happened on June 7, simultaneously with the mass arrival of passerines. In 1978 the first warm day was May 26, and the ice drift happened on June 7. Between these dates passerines arrived inactively; the birds were largely caught by nets from June 5 to June 15 at the Oktyabr’skii station. During both years snow remained until the beginning of June, the active melting coincided with the ice drift. A significant part of snow was thawed by the rains that began after the ice drift. In 1977 the warming began in the middle April. In late April the snow melted completely in tundra areas. In early May the snow melted completely in forest, too. The ice on the Ob’ River drifted on May 17. Passerines
arrived during all May, but more than half of the species registered in the Sob’ valley were first encountered between May 16 and May 25. April of 1982 was very warm, by the end of it all snow melted, and May was cold with recurrent snowfalls. The ice drift was observed on May 18. The arrival continued throughout May and the first ten-day period of June. In all other years May was relatively warm with recurrent colds; the ice drifted between May 25 and June 1; the mass arrival of passerines was observed most often in the last five days of May to the first ten days of June. The mass arrival is the period of a drastic increase in the numbers of birds on routes, in nets and traps. There can be both local individuals that have reached their destination and birds migrating northward. The summer in the Lower Ob’ region can be different but without snowfalls and negative temperatures. No influence of the summer characteristics over the times and duration of the seasonal phenomena of small birds has been recorded. Time of the beginning of autumn and winter in the Lower Ob’ region did not vary from year to year. The influence of Arctic is recorded sometimes at the end of August to the beginning of September as several days of cold rains and north wind. The first signs of autumn — yellowing of leaves and morning mists — are observed in late August. By mid-September the tree and shrub leaves fall. The morning frosts are more frequent since the second ten-day period of September. The tundra lakes usually become ice-bound at the end of September to the beginning of October. Snow settles in early or middle October. However, in 1982 winter began in the last days of September, and in 1975 — at the end of October. The majority of the singing birds fly away mostly in the third ten-day period of August or the first ten-day period of September regardless of the autumn’s characteristics. In 1982 the late migrants flew away earlier than usual. RESULTS AND DISCUSSION All materials on the dates and duration of the seasonal phenomena of passerines of the Lower Ob’ region are tabulated. For each section the extreme values for a several years (lim) and an average date and the number of observation years (n) are given. The table does not include the data on the species that nest farther to the north: shore lark (Eremophila alpestris L.) and snow bunting (Plectrophenax nivalis L.), sedentary species and species with incomplete data. All data for these years are cited in the text. The dates of the beginning of arrival. The spring migration of passerines in the Lower Ob’ region begins when the hood crows and snow buntings arrive and ends with the arrival of sand martins (Riparia riparia L.), Arctic warblers, sedge warblers (Acrocephalus schoenobaenus L.). Duration of the arrival period for passerines is 75–90 days. There are three waves of the
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arrival: in April, in early May, and from the end of May to the end of June. The first wave may include rooks (Corvus frugilegus L.) and common redpoll (Acanthis flammea L.) [11], in addition to snow buntings and hood crows. The first shore larks and white wagtails (Motacilla alba L.) arrive with the second wave when the ice-free patches appear on the Ob’ bank and the temperatures are above zero. When the thawed patches appear in the years with early and common springs, fieldfares (Turdus pilaris L.), reed buntings (Emberiza schoeniclus L.), bramblings (Fringilla montifringilla L.) begin to arrive. In the years with late springs this wave was absent, it combined with the last, basic wave of arrival. This wave begins with the mass arrival of common redpoll of the migratory form, which nests here irregularly. The wave ends, as was already said, when sand martins, Arctic and sedge warblers arrive. The arrival of hood crows began between April 1 and April 12, mostly on April 4–7, the average arrival date is April 7 (n = 8). First arrival of snow buntings was recorded between April 2 and April 16, the average arrival date is April 9 (n = 4). The first shore larks were encountered between May 1 and May 29, the average date is May 13 (n = 11). Since 1986 the dates of the beginning og migration in this lark shifted from the first half of May to its second half. According to the data of Paskhal’nyi [12], in the last decade the arrival of the larks began after May 17 both in the floodplains and on flat interfluve. The dates of arrival for the rest of the analyzed species are given in the table. The data on common redpoll concern the migratory form. The calculated mean annual dates of the arrival species correlate with the order of arrival in separate years. Of the birds included in the table the first to arrive were white wagtails (16.5), then fieldfares (20.5), reed buntings (21.5), common redpolls (22.5), redwings (24.5), and bramblings (26.5). The meadow pipits (Anthus pratensis L.), red-throated pipits (A. cervinus Pall.), willow warblers (Phylloscopus trochilus L.), bluethroats (Luscinia svecica L.), little buntings (Emberiza pusilla Pall.), and Lapland buntings (Calcarius lapponicus L.) began migration almost simultaneously, as inferred from averaged dates, at the end of May. The meadow pipits arrived earlier than the red-throated pipits, which is also evident from the averaged dates. In the first days of June yellow (Motacilla flava L.) and citrine wagtails (M. citreola Pall.), common chiffchaffs (Ph. Collybita Vieill.), common rosefinchs (Carpodacus erythrinus Pall.) began arriving; the first Arctic warblers (Ph. borealis Blas.) arrived no earlier than June 7. Duration of arrival. The period from encountering the first individual of a species to the end of flight of the northern species or to the end of formation of the local population of the Lower-Ob’ birds takes one to three weeks. The flight of snow buntings through the Ob’ region takes 40–49 days, 43.5 days on average (n = 3), the flight of shore larks takes 7–30 days, 17.5 days on aver-
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age (n = 8). In the years with late spring the flight of northern birds and formation of a local population takes less time. The flight duration in early year did not differ from that in middle year for the majority of species, but bramblings began to arrive with the first warming in May and continued up to 45 days in years with early spring. In some years the flight of common redpolls was long regardless of spring course, in 1980 and 1983 it lasted from the beginning of May to the end of the second ten-day period of June. The males of the majority of species arrived earlier than the females. The females of snow bunting arrived only in May, the females of yellow wagtails, bluethroats, redwings, willow and Arctic warblers, little buntings began to arrive three to seven days after the first males had arrived. Single females were present in the flocks of the first meadow and red-throated pipits; the flocks of common redpolls and Lapland buntings included both sexes equally. The males and females of bramblings arrived simultaneously, but in 1981 the females were first caught 10 days after the first male’s catch. In various years the formation of the local population of males in the test areas lasted 7 and 12 days for meadow pipits, 4 and 8 days for red-throated pipits, 8–13 days with an average of 9.7 (n = 4) for bluethroats, 12–19 days with an average of 15.2 (n = 4) for willow warblers, 4–8 days with an average of 5.5 (n = 4) for Arctic warblers, 12–16 days with an average of 13.7 (n = 4) for little buntings, and 9–19 days with an average of 15.1 (n = 4) for bramblings. As a rule, local populations of the other species in the control areas were also formed in no more than two weeks. Duration of the pre-nest period. The ornithological literature interprets the pre-nest period as an interval from the beginning of arrival of the first birds of a species to the start of egg-laying [5, 6, 13, 14]. The majority of the species in the table began egg-laying 10–15 days after the beginning of arrival. Since the females usually arrive later than the males, time is mostly spent to find a spouse and form a couple. The period from the beginning of the mass arrival of females to the start of egg-laying took almost invariably 8–10 days for the majority of the species, for which data are available. The ground-nesting birds built their nests in 4–6 days; bramblings and common redpolls built their nests on trees for 10 days [7]. The period from the moment of preempting the territory by the male to the first egg in the nest on its territory took: 9–14 days averaging 11.6±0.8 (n = 6) for bluethroats, 8, 9, 17 days for redwings, 9–19 days averaging 13.9 ± 1.1 (n = 9) for willow warblers, 7–14 days averaging 10.7 ± 1.0 (n = 7) for Arctic warblers, 6–13 days averaging 9.2 ± 0.5 (n = 16) for little buntings, 14 and 19 days for bramblings. The dates of the beginning of egg-laying. The main period when egg-laying starts in the Lower Ob’ region is June. Only hooded crows always began to lay eggs in May. In the years with early spring fieldfares, redwings,
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Dates lim/M (n) and duration lim/M ± m ( n ) of seasonal phenomena in passerines of the Lower Ob’ region Dates of beginning of arrival
Duration of arrival, days
Duration of prenesting period, days
Dates of beginning of egg-laying
Duration of the season of egg-laying, days
Dates of beginning of fledging
Anthus pratensis
20.5 - 4.6 29.5 (13)
5-8 9.2 ± 15 . (9 )
12 - 27 18.8 ± 21 . ( 7)
76 . - 18.6 14.6 ( 9 )
13 - 19 16.5 ± 15 . ( 4)
19.7 - 217 . 16.7 ( 6 )
Anthus cervinus
10.5 - 10.6 28.5 (10 )
5 - 14 7.4 ± 19 . ( 7)
7 - 17 12.0 ± 2.5( 4 )
9.6 - 216 . 16.6 (10 )
14 - 21 16.8 ± 13 . ( 5)
6.7 - 16.7 13.7 ( 6 )
Motacilla flava
19.5 - 12.6 2.6 (13)
5 - 25 10.5 ± 32 . (6 )
8 - 21 13.7 ± 21 . (6 )
116 . - 18.6 14.6 ( 8 )
12 - 20 172 . ± 19 . ( 4)
7.7 - 28.7 16.8 ( 8 )
Motacilla alba
4.5 - 2.6 16.5 (10 )
—
22 - 36 26.8 ± 2.2( 6 )
36 . - 20.6 136 . (10 )
15 - 27 19.8 ± 2.3( 5)
6.7 - 217 . 13.7( 9 )
Philloscopus trochilius
19.5 - 76 . 28.5 (15)
11 - 24 18.0 ± 13 . (10 )
12 - 26 20.9 ± 13 . (11)
10.6 - 24.6 18.6 (14 )
17 - 32 238 . ± 2.4( 6 )
10.7 - 23.7 15.7 ( 9 )
Philloscopus collybita
16 . - 116 . 36 . (6 )
6 - 20 10.3 ± 2.2( 6 )
18 - 28 22 ( 3)
156 . - 276 . 216 . (8 )
18 - 30 217 . ± 2.9( 4 )
16.7 - 27.7 217 . (8 )
Philloscopus borealis
76 . - 156 . 9.6 ( 9 )
5 - 14 10.0 ± 10 . (9 )
9 - 19 12.7 ± 14 . ( 7)
19.6 - 29.6 236 . (9 )
10 - 21 14 ± 21 . ( 5)
19.7 - 28.7 22.7 ( 6 )
Luscinia svecica
18.5 - 76 . 29.5 (15)
10 - 21 16.0 ± 11 . (11)
7 - 21 12.9 ± 14 . (10 )
10.6 - 20.6 16.5 (15)
12 - 27 19.6 ± 2.9( 5)
4.7 - 217 . 14.7 ( 9 )
Turdus pilaris
12.5 - 28.5 20.5 ( 7)
22 - 24 230 . (9 )
11 - 25 15.4 ± 2.7( 5)
255 . - 136 . 4.6 ( 8 )
17 - 35 24.7 ± 2.5( 7)
22.6 - 10.7 28.6 ( 8 )
Turdus iliacus
155 . - 2.6 24.5 ( 6 )
9 - 22 152 . ± 2.2( 6 )
8 - 14 11( 3)
255 . - 18.6 4.6 (10 )
13 - 22 20.7 ± 4.7( 4 )
20.6 - 10.7 28.6( 8 )
Fringilla montifringilla
155 . - 2.6 24.5 ( 6 )
13 - 42 235 . ± 3.7( 8 )
13 - 31 213 . ± 2.2( 8 )
9.6 - 24.6 18.6( 9 )
14 - 36 22.4 ± 4.4( 5)
8.7 - 26.7 17.7( 7)
Acanthus flammea
14.5 - 16 . 22.5 (12 )
6 - 34 24.4 ± 39 . (12 )
7 - 25 16 ± 35 . ( 5)
28.5 - 16.6 76 . (10 )
13 - 43 29.7 ± 73 . ( 4)
29.6 - 9.7 2.7 ( 4 )
Carpodacus erythrinus
14.5 - 16 . 22.5 (12 )
—
13 - 21 17 ± 13 . (6 )
16.6 - 22.6 18.6 ( 3)
18 - 23 20.5 ( 2 )
15.7 - 23.7 18.7 ( 3)
Emberiza schoeniclus
35 . - 76 . 215 . (10 )
7 - 30 16.6 ± 38 . (6 )
12 - 27 20 ± 3.7( 4 )
16.6 - 20.6 18.6 ( 6 )
21(1)
15.7 - 22.7 14.7 ( 5)
Emberiza pusilla
14.5 - 76 . 275 . (17)
6 - 19 14.8 ± 12 . (11)
6 - 26 155 . ± 19 . (11)
8.6 - 19.6 16.5 (15)
15 - 34 219 . ± 2.4( 8 )
5.7 - 17.7 10.7 ( 9 )
7 - 12 9.4 ± 0.7( 7)
8 - 17 136 . ( 3)
156 . - 22.6 18.6 ( 3)
12 (1)
10.7 - 14.7 13.7 ( 3)
Species
Calcarius lapponicus
30.5 - 12.6 29.5 (11)
and common redpolls began to lay eggs in the end of May. For the other species the average date of the beginning of egg-laying is the second ten-day period of June, for Arctic warblers and chiffchaffs it is the third ten-day period of June, i.e. the egg-laying begins after the average date of the summer beginning, June 10 [1]. In years with late spring the beginning of egg-laying
shifted to the third ten-day period of June for the majority of species. During all observation period small passerines began to lay eggs no earlier than 5 days after the temperature was above zero day and night. On the first day of egg-laying the mean daily temperature did not fall below 1.0 °C as inferred from the data for 4–7 years. The lowest temperature was recorded at the
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231
Duration of nesting season, days
Dates of beginning of post-breeding molting
Duration of post-breeding molting, days
Dates of beginning of post-juvenile molting
Duration of post-juvenile molting, days
Dates of departure, Juv/ad
Duration of season, days
38 - 44 415 . ± 16 . ( 4)
14.7 - 58 . 27.7
38.5 60 - 70
29.7 - 19.8 8.8 (1)
416 . (2 ) 55 - 65
258 . - 259 . 28.8 - 219 .
100 - 113 108.5 ( 4 )
36 - 43 38.8 ± 10 . (6 )
6.7 - 25.7 22.7
28.6 45 - 50
5.7 - 20.8 78 . (2 )
38.5 ( 3) 35 - 40
19.8 - 219 . 218 . - 8.9
104 - 115 110.5 ( 4 )
35 - 43 40.2 ± 19 . ( 4)
256 . - 18 . 16.7 (1)
29.7 55 - 60
17.7 - 9.8 19.7 (1)
431 . (1) 25 - 35
78 . - 39 . 158 . - 258 .
83 - 95 87.7 ( 3)
39 - 51 438 . ± 13 . ( 5)
2.7 - 29.7 16.7
42.9 60 - 70
217 . - 8.9 25.7 ( 3)
43.7 ( 3) 50 - 60
19.8 - 219 . 218 . - 259 .
114 - 139 119.5 ( 4 )
44 - 59 50.8 ± 2.4( 6 )
10.7 - 27.7 15.7 ( 5)
415 . ( 3) 55 - 65
20.7 - 24.8 78 . ( 4)
28.0 ( 3) 35 - 55
18.8 - 159 . 9.8 - 8.9
105 - 126 117.7 ( 4 )
43 - 55 46.5 ± 2.9( 4 )
20.7 - 73 . 27.7
319 . (1) 50 - 60
18.7 - 118 . 78 . (2 )
32.5 ( 2 ) 35 - 50
28.8 - 219 . 19.8 - 10.9
112 - 118 115 ( 2 )
35 - 41 39.0 ± 15 . ( 4)
13.7 - 28.7 10.7 (1)
22.8 (1) 35 - 40
No molting
No molting
10.8 - 26.8 4.8 - 24.8
74 - 80 76.2 ( 4 )
39 - 54 48.2 ± 2.9( 5)
5.7 - 317 . 24.7 ( 3)
38.7 ( 3) 55 - 65
20.7 - 218 . 18 . ( 4)
38.5 ( 4 ) 45 - 52
158 . - 119 . 16.8 - 18.9
108 - 115 111( 3)
39 - 51 40.7 ± 17 . ( 4)
17 . - 27.7 16.7
451 . 75 - 95
29.7 - 14.8 26.7
57.4 60 - 80
9.9 - 22.9 18.8 - 14.9
120 - 132 127 ( 3)
35 - 52 40.7 ± 17 . ( 4)
14.7 - 27.7 15.7
48.4 70 - 80
22.7 - 14.8 25.7
511 . 45 - 50
20.8 - 20.9 20.8 - 20.9
123 (1)
39 - 61 47.4 ± 4.2( 5)
10.7 - 4.8 12.7 ( 3)
56.6 ( 3) 75 - 85
4.8 - 22.8 16.8
39.9 40 - 50
10.8 - 59 . 258 . ± 18.9
102 - 137 112.2 ( 4 )
36 - 66 52.7 ± 51 . ( 4)
15.7 - 10.9 2.8 ( 5)
46.6 ( 5) 70 - 100
20.7 - 10.9 158 .
35 - 60 75 - 90
158 . - 1510 . 158 . - 1510 .
125 - 155 138 ( 3)
No molting
No molting
No molting
No molting
158 . - 22.8 158 . - 22.8
90 - 95 92 ( 3)
47 (1)
20.7 - 2.8 22.7
46.2 60 - 70
-8.8 24.7
46.2 60 - 75
19 . - 219 . 19 . - 219 .
104 - 138 122.7 ( 3)
35 - 54 418 . ± 2.4( 8 )
5.7 - 8.8 17.7 ( 8 )
42.5 ( 5) 55 - 65
10.7 - 158 . 22.7 ( 6 )
42.0 ( 6 ) 37 - 55
118 . - 139 . 10.8 - 10.9
98 - 133 112 ( 5)
29.7 55 - 60
18.7 - 29.7 23.7 (1)
413 . 40 - 50
238 . - 239 . 238 . - 239 .
107 - 126 119 ( 4 )
48 (1)
37 (1)
9.7 - 26.7 22.7
beginning of egg-laying by fieldfares — 1.0–11.5 °C in various years, 6.4 °C on average (n = 5); the highest temperature was registered for Arctic warblers — 5.6–21.8 °C with an average of 12.9 °C (n = 5) [7]. The duration of the egg-laying season. Of all the species represented in the table only some of redpolls have two normal clutches for the season [15], thus
stretching it up to 45 days. In other species the period is long because of repeated clutches. A second clutch was documented for the shore lark in southern Yamal [16]. In the Lower Ob’ region about 20% of the clutches perish [17], and some part of birds repeat nesting. The clutches that were found at the end of July or in August were considered to be repeated. Apart from the repeated
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clutches that are always present but not always found, the laying period lasts 2–3 weeks for all species. We should mention the high synchronism of the beginning of egg-laying: in the 80% of the control nests of all usual species first eggs were laid within 5–9 days. The synchronism does not increase farther northward. For example, in central Yamal in 1974 the beginning of egg-laying in 31 nests of Lapland bunting stretched for 20 days, with the beginning of laying in 21 nests within 6 days. In 1975 the beginning of laying in 19 nests stretched for 12 days [18]. Dates of the beginning of fledging. Generally, the chicks leave their nests in July, but the first fledglings of fieldfares and redwings left their nests at the end of June in most of the observation years. In some years the first common redpolls left their nests at the end of June. In forest-tundra the dates of fledging and further transition of the chicks to independent feeding coincide in time with the maximum abundance of dipterans the main food source of fledglings [19]. The dates of fledging are determined by the time of laying, duration of incubation and feeding. The last terms vary in different species as shown below. Duration of nesting season. The nesting season of a bird couple is a sum of laying, incubation, and feeding periods. In the studied region these stages are not overlapped only in the meadow pipit: It begins incubation only with the last egg, and the hatching takes no more than 24 hours [20]. White and yellow wagtails, willow warblers, Arctic warblers, and chiffchaffs begin to incubate only having laid half of the eggs, the rest of the species included in the table begin incubation since the first or second egg. The hatching stretched for 36–72 hours. White and yellow wagtails, meadow and red-throated pipits, bluethroats, fieldfares, redwings, willow and Arctic warblers incubated from laying the first egg to hatching the last chick for 17–22 days. Little and Lapland buntings, bramblings, common redpolls incubated for 15–19 days [1]. All species have their individual differences. For example, the female of willow warbler begins to incubate a clutch of 5 eggs since the 3rd egg and shortens the total incubation period for 24 h in comparison with the female that incubates a clutch of 7 eggs since the 4th egg. No doubt, the duration of incubation is influenced by the persistence of incubation. Both males and females of little bunting are involved in incubation and rarely expose the clutch; the female of red-throated pipit that incubates the equally open clutch leaves the nest each 5–15 minutes, it stays out of the nest for 1.5–3 h every 24 hours [20]. The incubation period for red-throated pipits lasts 18–21 days with an average of 19.5 ± 0.33, as opposed to 16–19 days with an average of 17.4 ± 0.16 for little bunting, respectively [7]. There are still no accurate experimental data testifying to the specific characteristics of the time of embryonic development of small passerines. Ornithologists from Perm’ [21] have divided the whole cycle of em-
bryogeny of passerines into 43 stages of development. To go through them all, the embryos of fieldfare and starling need 12 days, and the embryos of house sparrow need 11 days. In natural conditions the period from the last laid egg to the last hatchling (the period of the last egg incubation) reflects the rate of embryogeny to the utmost, because incubation passes under the conditions of the formed rhythm. In the Lower Ob’ region this period lasted no less than 11 days for fieldfare, Arctic warbler, little bunting, Lapland bunting, common redpoll; no less than 12 days for meadow pipit, bluethroat, redwing, brambling; no less than 13 days for white and yellow wagtails, red-throated pipit. The longest duration of incubation of the last egg for all species did not exceed 16 days. Under equal conditions the embryogeny of all northern birds lasts the same time, 11–12 days and all differences in the duration of incubation are determined by the behavior of adult birds. The chicks of northern passerines stay in nests of 7 to 14 days. Regular observations of the nests disturb the chicks. Upset, they leave the nest before the natural time. The disturbed little buntings left their nests especially early, on the 8th day of life. Red-throated and meadow pipit, Lapland buntings, redwings stayed in the nests no less than 9 days; yellow and white wagtails, fieldfares, bluethroats stayed no less than 10 days; willow and Arctic warblers, bramblings, common redpolls — no less than 11 days. The fledglings of little and Lapland buntings stay in nests for at most 11 days. For fledglings of the red-throated pipit, redwing, fieldfare, brambling, common redpoll the maximum is 12–13 days, for white wagtail, meadow pipit, bluethroat, willow and Arctic warblers it is 14–16 days. In the nests that were under observation from the beginning of egg-laying to the leaving of the last chick the total duration of the nesting period was the following: yellow wagtail — 24, 28, 30 days; white wagtail — 26–29 days with an average of 27.5 ± 0.5 (n = 6); red-throated pipit — 28, 30, 33 days; bluethroat — 27–35 days with an average of 30.3 ± 0.6 (n = 14); fieldfare — 25–27 days with an average of 26.2 ± 0.2 (n = 12); redwing — 24, 24 days; willow warbler — 28–33 days with an average of 30.4 ± 0.4 (n = 13); Arctic warbler — 28, 28, 30 days; little bunting — 20–26 days with an average of 22.7 ± 0.5 (n = 12); Lapland bunting — 24–28 days with an average of 25.6 ± 0.6 ( n = 7 ); brambling — 27, 27, 29 days; common redpoll — 23–29 days with an average of 26.0 ± 0.5 ( n = 13). The period from the first egg to the last fledgling varies from 35 days (for redwing, Arctic warbler and little bunting with no repeated clutches) to 66 days (for common redpoll with two clutches in one of the seasons). More often the nesting season lasted 40–55 days, up to the end of July–the first ten-day period of August. One nest of common redpoll was found in the second ten-day period of August within the observation period. The beginning of post-breeding molting. Of all species represented in the table the post-breeding molting
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in the nesting area is absent only for common rosefinch. Partial molt, when contour feathers of body, part of the vaned feathers of wings, rectrices and remiges are shed, was recorded for the Arctic warbler. The wing secondary feathers of willow warbler and chiffchaff are not always completely molted. The other species shed all contour feathers, all rectrices and remiges, and down of apteria [6]. The table shows the earliest and the latest dates of catching the birds that began molting in 1977–1984 (numerator) and the average date of the beginning of molting calculated with the help of regression analysis (denominator) [22]. For bluethroat, willow warbler, little bunting, brambling, common redpoll the denominator shows the mean annual date calculated by the average dates of the beginning of molting for several years (n). For the rare species the data of all years were summarized. In this case no (n) is given. In northern birds the post-breeding molting begins usually in July, but for redpolls in August, and for hooded crows in mid-June. In the first ten days of July molting birds were rare in the catch, from the second ten days they prevailed in the nets and traps. In early August willow warblers and bramblings without signs of molting were sometimes caught, and common redpolls covered with old feathers were caught until September 10. The period during which birds begin to molt lasts one month for the most of the populations of passerines of the Lower Ob’ region, and it lasts 40–50 days in the willow warbler, brambling, and common redpoll. The dates of the beginning of molting are coordinated with the breeding and coincide with chick feeding to a variable extent for various species. Some yellow wagtails combined the start of molting with incubation of the clutches of normal timing, the rest — with feeding. Red-throated pipit, little bunting, willow and Arctic warbler, brambling, presumably, fieldfare, redwing, Lapland bunting combine the molting with feeding the nestlings. White wagtail, meadow pipit, chiffchaff, reed bunting, some redpolls combined the start of molting with supplementary feeding of fledglings. All this is true for males. The molting of females more often coincides with supplementary feeding of fledglings [23]. The couples that incubated a late clutch started molting later than others, combining it with feeding the chicks to a greater extent. Duration of post-breeding molting. The table shows two numbers: the average duration of the molting of an individual (numerator) and duration of the molting season: from catching the first bird that started molting to catching the last bird finishing the molting (denominator). To calculate the molting duration for the rare species, the data of all years were summarized. In this case n is not given. For numerous species the molting duration for each year was calculated, and then the average duration for n years was counted. The duration of the molting season is given with the limits, where the minimum and the maximum were obtained in different years and approximated.
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Duration of the post-breeding molting of an individual depends on corpulence and size of the bird and the dates of molting. Arctic warblers that did not shed their rectrices and remiges molted for no more than 25 days, and willow warblers with the complete molt spent 37–46 days on it. Redwings and fieldfares molted longer than bluethroats of the same corpulence. The rate of molting depends on photoperiodic conditions, being higher on shorter days. That is why females of the species with sexual differentiation in terms of molting shed feathers faster, because it takes place in shorter days. For example, in 1978 the average date of the beginning of the molting for males of the willow warbler is July 7, for females — the 30th of July, the males molting for 46 days and females, for 33 days. The numbers for the brambling in 1978 are as follows: males began molting on July 4, females — on July 14, the molting lasting for 70 and 66 days, respectively. Unfortunately, the average seasonal duration of molting can be too low, for it was calculated by a small number of dates, among which there were little data on the birds that begin and finish molting. Particularly, feather change for yellow wagtail, red-throated pipit, chiffchaff, Lapland bunting lasted 40–45 days in the open-air cages during light days, not 28–32 days as was calculated by the dates of catching the birds in molt and given in the table. The shortest period of the post-breeding molting is registered for the Arctic warbler (no more than 40 days). The molting season lasts up to three months for the fieldfare, redwing, brambling, and more than three months for common redpoll. Arctic warblers that had nearly finished molting were caught from mid-August; the redwings and bramblings whose molt came to a close were caught in mid-September; fieldfares — at the end of September, and the common redpolls that were still molting intensely — in October. In 1976 and 1978 the molting season of the latter species lasted till the end of October. The rest of the species in the table finished molting at the end of August to the beginning of September; their molting season lasted about two months. The beginning of post-juvenal molting. Of the discussed species, Arctic warblers and common rosefinches did not shed their youth feather to acquire the first winter plumage in the hatching area. Shore lark molted completely or close to that. A partial molt is typical of the rest of the species, when the bird displays a mixed plumage, consisting of the youth rectrices and remiges, and the vaned feathers of wings and body replaced as a result of molting. The interspecific distinctions in the completeness of molt mostly concern the vaned feathers of wing: from replacing solely the lower vaned feathers of propatagium for willow warbler to replacing the majority of the vaned feathers for little bunting [6]. The secondary remiges can be replaced in some yellow wagtails, meadow pipits, redwings, little buntings, and common redpolls. Of the vaned feathers of body those feathers that began growing during nest period (the central rows) participate in molting. The upper and lower
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vaned feathers of tail were not shed in the majority of observed willow warblers and some red-throated pipits. The main period for passerines of the Lower Ob’ region to enter the post-juvenile molting is the end of July to the first half of August. The average dates of the beginning of molting belong to the same period. Percentage of the birds that began molting in the second half of August is insignificant; mainly, these are birds from repeated clutches. However, all bramblings that began molting were caught in August. In 1977 and 1982 it took two months for common redpolls to enter the molting. The beginning of the post-juvenile molting for the majority of northern species is coordinated with hatching. Particularly, a positive correlation of the dates was determined for the bluethroat (r = 0.95) and little bunting (r = 0.89). It is explained by the fact that these species have a fixed age for the beginning of molting — 20–25 days for the bluethroat and 18–23 days for the little bunting. In the subarctic zone these birds are predominant: yellow, white and citrine wagtails, redthroated pipit, fieldfare, willow warbler, chiffchaff, reed and Lapland bunting began molting while being no more than 27–30 days of age. At the same time the meadow pipit, redwing, and common redpoll began molting depending on photoperiodic conditions between 25–45 days after hatching. The snow bunting of northern Yamal also begins molting in accordance with photoperiod [6]. Since the nights north of the Arctic Circle become dark in late July, the molt of the last four species is supposed to begin in the later time and at a later age. The table shows it only for common redpolls: their average date of the beginning of molting is in middle August. During three seasons out of four the redpolls that began to shed feathers were caught from the second five-day period of August to September, which is considerably later than in other species with earlier hatching. Duration of the post-juvenile molting. The section concerns the same parameters as for the post-breeding molting: the table shows the average duration of molting of an individual (numerator) and duration of the molting season (denominator). Duration of molting of young birds as well as the adult birds depends to some extent on the bird’s size and to a greater extent on completeness of molt. For example, the average seasonal duration of molting for the willow warbler that shed only some part of contour feathers of body varied from 25 to 31 days in various years with an average of 28.0 (n = 3). For the little bunting that shed all contour plumage and a bigger part of the vaned feathers of wing the molting lasted 37–50 days in various years with an average of 42.0 (n = 6). Since this molt for the majority of the northern species is not complete and, therefore, does not hinder active flight, it is often combined with migration. That is why the molting season (denominator) may be very
short. In particular, molting yellow wagtails were recorded on the territory of the Lower Ob’ region for 25–35 days in various years (with an average duration of molting of 41 days for an individual), and their departure took place during the 5–6th (of 7 determined) stages of molting. The red-throated pipit, bluethroat, redwing, willow warbler, chiffchaff, little bunting, and brambling start migration while molting. The white wagtail, meadow pipit, fieldfare, reed and Lapland bunting begin migration at the last stage or in the new plumage, so their molting season lasts 2–3 months. Among caught white wagtails, red-throated and meadow pipits, bluethroats, willow warblers, little, reed and Lapland buntings, and common redpolls there could be individuals from the more northern regions that molted at longer days (on central and northern Yamal day begins to shorten later), which stretches the season’s duration. Start of migration. In the subarctic zone the autumn migration of passerines is hardly noticeable: a gradual decrease in number and disappearance of birds is recorded on the routes, in nets or traps. Flying from the north were flocks of the shore lark, white wagtail, meadow and red-throated pipits, reed, snow and Lapland buntings, and common redpolls. The dates of the start of migration for the adult birds (denominator) were determined by the dates when the birds that have almost shed the secondary feathers were caught. The date of the start of migration for the young birds was determined by the time when the birds in the stages of molting that are typical of those participating in migration appeared in the nets. The birds begin to leave the Lower Ob’ region in the first or second ten-day period of August and finish in late October–early November. The first to leave are sand martin, Arctic warbler, and yellow wagtail, and the last, the snow bunting and hooded crow. The main period of departure for insectivorous species falls on the third ten-day period of August and the first ten-day period of September. In the second half of September the white wagtail, meadow pipit, fieldfare, redwing, reed and Lapland buntings, brambling, the majority of common redpolls and hooded crows leave forest-tundra. Climate conditions did not seem to influence the time of departure; it happens under more favorable climate conditions than arrival. The birds that leave in August do not experience temperatures lower than +10 °C; there were no subzero temperatures and snowfalls in the first half of September. The biomass of insects — the main food for the majority of northern passerines — decreases at the end of August and is likely to influence the date of departure. However, the main factor that determines when an individual is ready to migrate is the formation of migratory state. For the adult birds of the Lower Ob’ region the migratory state usually forms at the last, 11th stage of molting, when the remiges of wing tip and the majority of the secondary remiges have grown. The local birds disappeared from the control area in just such a state,
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with the 14–16th remiges having almost grown. During the previous 7–10th stages many northern passerines lose their ability to fly [23, 24]. Since the time of this molting depends on the time of nesting, which in turn depends on the time of arrival, the date of departure is actually determined in spring. In the years with late spring the migration shifts to later dates. During the post-juvenile molting the flying properties of wing are not lost, and many species combine the formation of the migratory state with molting. The former is strongly coordinated with the dates of hatching, especially for the species with the fixed age of the beginning of molting. Analysis of the dates of hatching and departure for the bluethroat, willow warbler, and little bunting in 1977–1982 showed a high positive correlation between the dates [6]. The departure of bluethroats ended 71–74 days with an average of 71.3 days (n = 5) after the beginning of hatching (r = 0.98), willow warblers finished their departure in 60–68 days with an average of 64.5 days (n = 4) after the beginning of hatching (r = 0.82); little bunting — in 67–77 days with an average of 71.3 days (n = 6) after the beginning of hatching (r = 0.56). It is possible to predict the time of departure for these birds by the time of egg-laying. For the birds whose post-juvenile molting is controlled by photoperiodicity (meadow pipit, redwing, and redpoll) the dates of departure do not depend as much on the dates of hatching and their departure is stretched. Duration of the spring-summer-autumn season. The Arctic warbler stays in the studied area for the shortest period of time (2.5 months). The stay of the sand martin in the Lower Ob’ region is not much longer. The yellow wagtail and common rosefinch stay up to three months. They arrive at the end of spring, but depart before the beginning of autumn. Citrine and white wagtails, meadow and red-throated pipits, bluethroat, willow warbler, chiffchaff, little and Lapland buntings, and bramblings stay in forest-tundra no more than four months, usually 100–115 days; the shore lark, fieldfare, redwing, reed bunting, and common redpoll stay up to five months, and the snow bunting and hooded crow — up to six months. In the years with early spring white wagtails were seen in the Ob’ valley for longer than four months, reed buntings — longer than five months. Sedentary passerines of the Lower Ob’ region. At the latitude of the Arctic Circle the species composition of regularly hibernating passerines is very wide. In the Lower Ob’ region it includes the Siberian tit (Parus cinctus Bodd.), common redpoll, European magpie, Siberian jay (Perisoreus infaustus L.), common raven (Corvus corax L.), house (Passer domesticus L.) and tree (P. montanus L.) sparrows. Sometimes in winter one can see the great tit (Parus major L.), willow tit (P. montanus Bald.), Eurasian nuthatch (Sitta europaea L.), two-barred crossbill (Loxia leucoptera Gm.), pine crossbeak (Pinicola enucleator L.), bullfinch (Pyrrhula pyrrhula L.). White-throated dipper (Cinclus cinclus L.) can be encountered in the nonfreezing parts
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of the rivers of the Polar Urals. The nesting of all these birds has been proved except European nuthatch. The common redpoll is nomadic [11]. In mild winters it does not leave forest-tundra, in cold winters it migrates to northern taiga. The times and duration of the seasonal phenomena for these species differ little from those of the migratory species. Ravens and magpies nest and molt simultaneously with hooded crows. The Siberian tit begins to lay eggs no earlier than fieldfare; their post-breeding molting begins before their chicks become fledglings (for some males — during nest time), the post-breeding and post-juvenile molts end by mid-October. House and tree sparrows make two clutches per season. Reproduction begins in June and lasts until mid-August. In August the molting begins, which lasts until the end of October for the birds of the second clutch and some adult individuals. Some tree sparrows from villages of the Lower Ob’ region leave for south. Probably, these are the birds that finished their molting early, while the birds that finish it in the beginning of winter stay. CONCLUSIONS The cycle of the first year of life of birds is formed by growth-development, nesting of the young, post-juvenile molting, autumn migration, hibernation, prebreeding molting, spring migration, and pre-breeding activity. In succeeding years the cycle consists of sexual activity, post-nesting transfers, post-breeding molting, autumn migration, hibernation, and pre-breeding molting, spring migration, and pre-breeding activity [25]. The annual cycle of the considered species is a more or less reduced version of seasonal phenomena, varying in dates and duration. It depends on genesis of the birds, history of the area assimilation, conditions of the environment, and some other factors. The time of certain phenomena of the summer part of annual cycle for passerines of the Lower Ob’ region is determined by the dates of arrival and formation of a local population of species. The later spring comes, the later the migrants arrive. As soon as the daily temperatures stop dropping below zero, the egg-laying begins. The dates of the following events — end of incubation, fledging, beginning and end of molting, formation of migratory state, and departure — can be rather accurately calculated by counting the number of days from the date of the beginning of egg-laying. The total duration of the stay of a species in the nesting area depends on temperature. Frost-free season at the latitude of Salekhard lasts three months. It embraces the complete “summer” part of the annual cycle of the sand martin, yellow wagtail, Arctic warbler, and common rosefinch. The four species have the same bordering limit — shrub tundra. If these birds stay in the nesting area for a shorter period, it is accompanied by shift of molting to the “winter” period (sand martin and common rosefinch), reduction of the post-breeding molting and shift of the post-juvenile molting to winter
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(Arctic warbler), combination of the post-breeding molting with incubation and feeding and combination of the post-juvenile molting with migration for yellow wagtail. The great gray shrike (Lanius excubitor L.), Siberian jay, European magpie, hooded crow, Siberian accentor (Prunella montanella Pall.), lesser whitethroat (Silvia curruca L.), common redstart (Phoenicurus phoenicurus L.), Siberian tit, brambling, pine crossbeak, two-barred crossbill, bullfinch, and some other rare taiga species almost never go from forest-tundra to tundra. Complete post-breeding molt, and partial, but close to complete, post-juvenile molt are typical of all the species. The short summer is likely to prevent such insectivorous species as lesser whitethroat, common redstart, and Siberian accentor from going farther northward (they are observed in forest-tundra for 3 months), but the main limiting factor here is the absence of trees necessary for nesting. All other birds of this group are able to stay in forest-tundra until the late autumn or all year round, i.e., they depend on the shortness of summer even less, but they also need trees or treelike shrubs for nesting. Citrine and white wagtails, meadow and red-throated pipits, bluethroat, willow warbler, chiffchaff, little, reed and Lapland buntings arrive at forest-tundra as the snow begins melting actively and leave before snowfalls. They have complete post-breeding and partial post-juvenile molting; combine the post-breeding molting with feeding the nestlings; have endogenous control of the beginning of the post-juvenile molting (except meadow pipits with photoperiodic control of molting); combine the end of the post-juvenile molting with migration. The boundary of distribution of the white wagtail, red-throated pipit, and Lapland bunting runs through the Arctic tundra. The rest of the species stop at moss-lichen tundra of central Yamal. In forest-tundra the period from arrival to departure of these species lasts 3–4 months, and the local birds usually spend less than 3 months between occupation of the territory and departure, i.e., these species manage in forest-tundra in the frost-free period. In tundra of central Yamal the departure of all passerines, except snow bunting, ends at the beginning of September [6]. Considering the later arrival [4], the spring-summer season on the northern boundary of the natural habitat of these species lasts also less than 3 months, but with 2 months of above-zero temperatures. Besides the mentioned species, the shore lark, sedge warbler, Northern wheatear (Oenanthe oenanthe L.), fieldfare, redwing, common redpoll, Pallas’s reed (Emberiza pallasi Cab.) also stop nesting in the belt between the 70th and the 71st latitude. Summer in the arctic tundra of northern Yamal lasts less than 2 months. To reproduce successfully and depart in time white wagtails and red-throated pipits that nest there must arrive and nest phenologically earlier than in forest-tundra and southern tundra, combine
feeding the nestlings and post-breeding molting; post-juvenile molting and migration; have a high rate of molting during the round-the-clock polar day. No doubt, all this takes place, because the birds cross central Yamal no later than the beginning of September, and forest-tundra — in the second half of September. The same is true for the Lapland bunting. In spite of the plant seeds prevailing in the autumn food supply, and thus, less dependence on the shortage of autumn food, Lapland buntings fly simultaneously with pipits and wagtails. Only snow buntings do not run away from the advent of winter. REFERENCES 1. V. V. Orlova, Climate of the USSR, Vol. 4 (Gidrometeoizdat, Leningrad, 1962) [in Russian]. 2. V. B. Zimin, Ecology of Passerines of the Northwest of the USSR (Nauka, Leningrad, 1988) [in Russian]. 3. N. N. Danilov, Ways of Adaptation of the Ground Vertebrates to the Conditions of Existence in Subarctic Zone, Vol. 2: Birds (Sverdlovsk, 1966) [in Russian]. 4. V. N. Ryzhanovskii and V. K. Ryabitsev, in Ecology and Biocenotic Relationships of Migratory Birds of the West Siberia (Novosibirsk, 1981), pp. 185–192 [in Russian]. 5. V. K. Ryabitsev, E. A. Polents, N. S. Alekseeva, Yu. A. Tyul’kin, et al., Ekologiya, No. 3, 1 (1999). 6. V. N. Ryzhanovskii, Ecology of the Post-Nesting Period of Life of Passerine Birds of the Subarctic Zone (Yekaterinburg, 1997) [in Russian]. 7. V. N. Ryzhanovskii, in Nest Life of Birds (Perm, 2001), pp. 3–18 [in Russian]. 8. G. A. Noskov and T. A. Rymkevich, in Methods of Research of Productivity and Structure of Species within Their Natural Habitats (Vil’nyus, 1977), pp. 37–48 [in Russian]. 9. T. I. Blyumental’ and V. R. Dol’nik, in Proceedings of the All-Union Conference on the Intraspecific Variability of Ground Vertebrates and Microevolution (Sverdlovsk, 1966), pp. 319–332 [in Russian]. 10. T. A. Rymkevich and V. N. Ryzhanovskii, in Ornithology (Mosk. Gos. Univ., Moscow, 1987), Iss. 22, pp. 116– 117 [in Russian]. 11. V. N. Ryzhanovskii, Russkii Ornitologicheskii Zh., Express-Issue 58, 9 (1999). 12. S. P. Paskhal’nyi, in Longstanding Dynamics of the Number of Birds and Mammals in Relation to the Global Climate Change (Novoe Znanie, Kazan’, 2002), pp. 151– 156 [in Russian]. 13. S. M. Uspenskii, Life at High Latitudes (Mysl’, Moscow, 1969) [in Russian]. 14. A. A. Fufaev, in Nest Life of Birds (Perm, 1984), pp. 110–113 [in Russian]. 15. N. S. Alekseeva, in Ornithology (Mosk. Gos. Univ., Moscow, 1986), Iss. 21, p. 145 [in Russian]. 16. V. K. Ryabitsev and Yu. A. Tyul’kin, Ornithology (Mosk. Gos. Univ., Moscow, 1986), Iss. 20, pp. 80–81 [in Russian].
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DATES AND DURATION OF THE BASIC SEASONAL PHENOMENA 17. V. N. Ryzhanovskii, V. K. Ryabitsev, and Yu. M. Malafeev, Zoologicheskii Zh. 53 (2), 305 (1974.). 18. N. N. Danilov, V. N. Ryzhanovskii, and V. K. Ryabitsev, Birds of Yamal (Nauka, Moscow, 1984) [in Russian]. 19. V. N. Ol’shvang, Structure and Dynamics of Population of Insects of Southern Yamal (Yekaterinburg, 1992) [in Russian]. 20. V. N. Ryzhanovskii, Fauna of Subarctic Zone and West Siberia (Sverdlovsk, 1987), pp. 3–13 [in Russian].
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21. M. Bolotnikov et al., Ecology of Early Ontogenesis of Birds (Sverdlovsk, 1985) [in Russian]. 22. S. L. Plimm, Condor 78 (4), 550 (1976). 23. V. N. Ryzhanovskii, Ekologiya, No. 3, 31 (1987). 24. N. N. Danilov, Fauna of Northern Ob’ Region and Its Use (Tyumen’, 1959), pp. 390–392 [in Russian]. 25. G. A. Noskov and T. A. Rymkevich, Dokl. Akad. Nauk SSSR 301 (2), 505 (1988).
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