Soaring bird migration is a subject of quantification in NE Bulgaria. The spatial and temporal distribution of birds in NE Bulgaria is described in details. The pattern of soaring bird migration indicate strong impact of wind on seasonal distribution of bird numbers across the flat area of agricultural fields along this part of Bulgaria.

1. The magnitude and timing of
autumn and spring migration
of soaring birds in NE Bulgaria.
Dimitar Dimitrov, Pavel Zehtindjiev
Institute of Biodiversity and Ecosystem Research
Bulgarian Academy of Sciences
Kalimok Station
e-mail: pavel.zehtindjiev@gmail.com

2. Study area in respect to main bottlenecks of
soaring bird migration
Study area

3. LOCATION OF OBSERVATION POINT
162 m a.s.l.
Provadiapoint
Provadia point

4. MATERIALS AND METHODS
• Visual observations were made in one year - 2005 – 38 days in spring
and 89 days in autumn.
• Investigation was made at one observation point in hours from 7 AM
to 7 PM with binoculars Nikon 10x50 and telescope Nikon 15-45.
• Birds were count one by one, or on groups with 5-th, 10-th or 100-th.
• For species determination Svensson 1999 Bird Guide was used.
• Altitude was defined visually. By the proportion of the electricity poles
(land marks) and relative bird size of every species.
• Flight direction was determine visually with compass.
• We determine distance from bird to the observation point using
topography map.
• Meteorological indexes: temperature with thermometer [ºC], wind
direction with compass [16 sectors], strength of the wind visually in 6
degree,

5. BIRDS SPECIES STRUCTURE
• 83 BIRD SPECIES – 30 SOARING
BIRDS = 26 RAPTORS + 4
WATERFOWL
• 53 OTHER BIRDS
• TOTAL COUNT OF BIRDS IS
75192 = 18559 SPRING + 56633
AUTUMN
• COUNT OF SOARING BIRDS
58419 = 15866 SPRING+ 42553
AUTUMN
• THE MOST NUMEROUS
SPECIES IS WHITE STORK
/Ciconia ciconia/ - 62% OF BIRDS
IN AUTUMN AND 67% OF BIRDS
IN SPRING
разпределение на групите
птици проле т 2005
водолюби
ви видове
68%
грабливи
видове
17%
други
видове
15%
разпределение на групите
птици е с е н 2005
водолюби
ви видове
63%
грабливи
видове
12%
други
видове
25%
GROUP DISTRIBUTION OF BIRDS
IN SPRING 2005
OTHER
SPECIES
15%
RAPTORS
17%
STORKS AND
PELECANS
68%
OTHER
SPECIES
25%
RAPTORS
12%
STORKS AND PELECANS
63%
GROUP DISTRIBUTION OF BIRDS
IN AUTUMN 2005

6. No Latin name Spr Aut Total No Latin name Spr Aut Total
1 Pernis apivorus 39 1767 1806 20 Aquila heliaca 1 2 3
2 Milvus migrans 30 8 38 21 Aquila chrysaetos 4 0 4
3 Milvus milvus 1 1 2 22 Hieraaetus pennatus 18 30 48
4 Neophron percnopterus 6 10 16 23 Pandion haliaetus 6 3 9
5 Circaetus gallicus 58 63 121 24 Falco tinnunculus 28 25 53
6 Circus aeruginosus 134 119 253 25 Falco vespertinus 69 108 177
7 Circus cyaneus 19 18 37 26 Falco columbarius 1 0 1
8 Circus macrourus 25 3 28 27 Falco subbuteo 8 15 23
9 Circus pygargus 3 21 24 28 Falco peregrinus 0 2 2
10 Circus spp. 15 44 59 29 Falco spp. 3 21 24
11 Accipites gentilis 40 37 77 30 Falconiformes 74 56 130
12 Accipiter nisus 292 270 562 Total raptors 3181 6729 9910
13 Accipiter brevipes 3 8 11 31 Ciconia ciconia 12421 35220 47641
14 Accipiter sp. 3 13 16 32 Ciconia nigra 56 199 255
15 Buteo buteo 1111 1218 2329 33 Pelecanus onocrotalus 147 405 552
16 Buteo rufinus 22 22 44 34 Pelecanus crispus 1 0 1
17 Aquila pomarina 1168 2840 4008 35 P. onocr./crisp 60 0 60
18 Aquila clanga 0 2 2 Total waterfowl 12685 35824 48509
19 Aquila nipalensis 0 1 1 Total soaring 15866 42553 58419
REGISTERED BIRD SPECIES

7. PERIOD OF SOARING BIRDS MIGRATION
ПЕРИОДИ НА ПРЕЛЕТ ПРОЛЕТ 2005
7,72% 8,62%
5,56%
9,96%
8,07%
13,54%
9,74%
36,80%
0,00%
5,00%
10,00%
15,00%
20,00%
25,00%
30,00%
35,00%
40,00%
23-27Март 28Март-
01Април
02-06Април 07-11Април 12-16Април 17-21Април 22-25Април 26-29Април
период (дата)
ПЕРИОДИ НА ПРЕЛЕТ ЕСЕН 2005
0,59%
4,81%
60,71%
22,16%
2,87%
6,11%
1,27% 0,93% 0,55%
0,00%
10,00%
20,00%
30,00%
40,00%
50,00%
60,00%
70,00%
01.08-
10.08
11.08-
20.08
21.08-
30.08
31.08-
09.09
10.09-
19.09
20.09-
01.10
02.10-
11.10
12.10-
21.10
22.10-
30.10
а в г у с т с е п т е м в р и о к т о м в р и
период (дата)
PERIODS IN SPRING 2005
PERIODS IN AUTUMN 2005
23-27
March
28 March-
01 April
02-06
April
07-11
April
Period (date)
12-16
April
17-21
April
22-25
April
26-29
April
A u g u s t S e p t e m b e r O c t o b e r
Period (date)

8. COMPARISON ON THREE MOST NUMEROUS SOARING BIRDS
IN SPRING
0,00%
10,00%
20,00%
30,00%
40,00%
50,00%
60,00%
70,00%
23-27Март 28Март-
01Април
02-06Април 07-11Април 12-16Април 17-21Април 22-25Април 26-29Април
период
A.pomarina
B.buteo
C.ciconia
period
23-27
March
28March-
01April
02-06
April
07-11
April
12-16
April
17-21
April
22-25
April
26-29
April

9. COMPARISON ON THREE MOST NUMEROUS SOARING BIRDS
IN AUTUMN
0,00%
10,00%
20,00%
30,00%
40,00%
50,00%
60,00%
70,00%
80,00%
01.08-10.08 11.08-20.08 21.08-30.08 31.08-09.09 10.09-19.09 20.09-01.10 02.10-11.10 12.10-21.10 22.10-30.10
а в г у с т с е п т е м в р и о к т о м в р и
период
A.pomarina
C.ciconia
P.apivorus
A u g u s t S e p t e m b e r
period
O c t o b e r

10. DAILY DYNAMICS OF SOARING BIRDS
дневна активност на реещите птици през пролетта
0,02% 0,01%
1,28%
10,24%
14,86%
21,78%
8,04% 8,56%
5,04%
1,55%
0,30% 0,23%
28,11%
0,00%
5,00%
10,00%
15,00%
20,00%
25,00%
30,00%
6h. 7h. 8h 9h. 10h. 11h. 12h. 13h. 14h. 15h. 16h. 17h. 18h.
час
дневна активност на реещите птици през есента
6,48% 6,78%
13,47%
11,35%
12,85%
6,55% 6,67%
14,22%
2,75%
2,23%
0,14%
16,51%
0,00%
2,00%
4,00%
6,00%
8,00%
10,00%
12,00%
14,00%
16,00%
18,00%
7h. 8h. 9h. 10h. 11h. 12h. 13h. 14h. 15h. 16h. 17h. 18h.
час
Daily activity of soaring birds in spring
Daily activity of soaring birds in autumn
hour
hour

11. DAILY DINAMICS IN AUTUMN
часова динамика по месеци
ЕСЕН 2005
0,00%
5,00%
10,00%
15,00%
20,00%
25,00%
30,00%
35,00%
7h. 8h. 9h. 10h. 11h. 12h. 13h. 14h. 15h. 16h. 17h. 18h.
час
август
септември
октомври
hour
Hour dynamics in Autumn 2005
Aug
Sep
Oct

12. FLIGHT ALTITUDE
височинно разпределение на реещите птици
ПРОЛЕТ 2005
4,55%
98,82%
0,01%
0,08%
0,00% 20,00% 40,00% 60,00% 80,00% 100,00% 120,00%
0 -499
500-999
1000-1499
над 1500
ниска
средна
висока
най-
висока
ALTITUDE
(m)
височинно разпределение на реещите птици
ЕСЕН 2005
57,00%
47,23%
5,14%
0,00%
0,00% 10,00% 20,00% 30,00% 40,00% 50,00% 60,00%
0 -499
500-999
1000-1499
над 1500
ниска
средна
висока
най-
висока
ALTITUDE
(m)
Altitude distribution of soaring birds
Spring 2005
Altitude distribution of soaring birds
Autumn 2005

13. FLIGHT DIRECTION OF SOARING BIRDS
Spring 2005
Mean vector /red/ 352.75°
Length of mean vector 91%
Standard deviation 24.53°
Rayleigh test of uniformity (p) 0.00
Autumn 2005
Mean vector /red/ 178.72°
Length of mean vector 91%
Standard deviation 25.51°
Rayleigh test of uniformity (p) 0.00

14. INFLUENCE OF METEOROLOGICAL FACTORS IN AUTUMN
влияние на температурата върху интензивността на
прелета
0,00%
5,00%
10,00%
15,00%
20,00%
25,00%
30,00%
35,00%
40,00%
45,00%
50,00%
0,0 - 4,5 5,0 - 9,5 10,0 - 14,5 15,0 - 19,5 20,0 - 24,5 25,0 - 29,5 30,0 - 34,5 35,0 - 39,5
температура в градус С
общо реещи
водолюб.
грабливи
Temperature and migration
intensity
Total
soaring
waterfowl
raptors
Temperature (ºC)

15. INFLUENCE OF METEOROLOGICAL FACTORS IN AUTUMN
СИЛАНАВЯТЪРА
7%
57%
16%
7%
6%
7%
Безветрие
Слаб
Слаб до умерен
Умерен
Умерен до силен
Силен
Wind velocity
No wind
Weak wind
Weak-middle
Middle wind
Middle-strong
Strong wind
влияние на посоката на вятъра върху количеството
реещи птици през есента
%0
%01
%02
%03
N
NNE
NE
ENE
E
ESE
SE
SSE
S
SSW
SW
WSW
W
WNW
NW
NNW
количество на
реещите птици
0
Wind direction
Proportion
of birds

16. ВЕП
Мировци
Large front of spring soaring bird migration in NE Bulgaria
VISUAL OBSERVATIONS

17. ВЕП Исперих
Large front of autumn soaring bird migration in NE
Bulgaria
VISUAL OBSERVATIONS

18. 240859
44398
8488
4922
3904
5525
AUTUMN 2009
Large front of autumn soaring bird migration in NE
Bulgaria
VISUAL OBSERVATIONS

19. 54127
20954
20127
32051
12812
8386
6521
6497
1008
Autumn 2010
Large front of autumn soaring bird migration in NE
Bulgaria
VISUAL OBSERVATIONS

20. CONCLUSIONS
1. Around 60,000 soaring birds from 30 species – 26 raptors and 4 water
birds cross every spring and autumn in large front territory of NE
Bulgaria.
2. The most numerous species was White Stork (Ciconia ciconia) with
62% in spring and 67% in autumn.
3. The period with most intensive migration in spring is between 7 and 16
April – 50% of birds, in autumn the same period is between 21 and 30
August – 60% of birds.
4. Daly activity is most intensive between 11 and 12 h in spring, and from
10 to 11 h in autumn.
5. The flight direction of all registered soaring birds in spring is between
328 º and 376 º, and between 153 º and 203 º in Autumn.
6. Spatial distribution of soaring birds over NE Bulgaria is determined by
the wind direction during the period of seasonal migrations and there is
no constant MIGRATION ROAD of birds crossing this territory.
7. Obtained results are of high value concerning the wind power industry
and collision risk for the migrating birds in the region of NE Bulgaria.