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Relationship between the Intensity of Nocturnal Migration Measured by Radar and the Anthropogenic Mortality of Birds


Abstract and Figures

Between August 27th and September 30th 2014 the intensity of nocturnal bird migration was measured in the Dobrudzha Region (NE Bulgaria) using a specific bird radar. During the same time period and in the same area (part of Natura 2000 net BGSPA0002051 Kaliakra and adjacent areas), road-kills as well as collisions of birds with wind turbines were recorded. Along a 9-km-long secondary road, 95 dead birds out of 24 species belonging to six orders were found. A systematic carcass search under 52 wind turbines was examined and eight collision victims belonging to five bird species of four orders were discovered. The results did not show a relation between bird mortality due to wind turbine collisions and nocturnal migration. However, a positive correlation between night passerine migration intensity and road mortality of passerines was found. Windfarms do not appear to be more detrimental to migrating birds than other anthropogenic sources of mortality, such as automobile traffic. The recorded high number of road-kills in the designated Natura 2000 zone Kaliakra provides a basis for planning additional restrictions in this zone, in order to secure the habitats, which are important for migrating passerine birds.
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Acta zool. bulg., 69 (2), 2017: 229-237
*Corresponding author:
Terrestrial Ecology and Behaviour
Research Article
Bird migration is an impressive natural phenomenon
that has been described in many scientic publica-
tions, summarised mainly by AlerstAm (1990),
Berthold (2001), Bildstein (2006) and newton
(2010). Some of the papers are devoted to migration
over the Balkan Peninsula, which is a territory with an
intensive bird migration (dontchev 1980, Bildstein
& ZAlles 1995, michev et al. 2011, shurulinkov et
al. 2011, Zehtindjiev 2001a). Bird migration is dom-
inated by nocturnal migrants (Bruderer & liechti
1995, 1999) where passerine birds constitute a major
part (Bloch et al. 1981, rABenold 1993). Many of
them are long-distance migrants wintering in sub-
Saharan Africa. Large-scale distribution and dy-
namics of nocturnal migration particularly over the
Balkans and Bulgaria were studied through a direct
moon watching technique (BolshAkov et al. 1998,
Zehtindjiev 2001a, b, Zehtindjiev & liechti 2003).
Soaring bird migration across Bulgaria has
been studied systematically in different locations
by visual observations (Bildstein & ZAlles 1995,
michev et al. 2011, 2012, shurulinkov et al. 2011).
In the early 1980s synchronised visual and airport ra-
dar observations were carried out for the rst time in
Bulgaria (michev et al. 1987). The main advantages
of radar observations compared to visual observa-
tions are their objectiveness due to the independence
between daylight and visibility (SchmAljohAnn et al.
2008, dokter et al. 2009). Unfortunately, the cur-
rently used radar systems do not provide enough in-
formation about the species composition and details
about single species migration. Therefore, little is
known about the spatial and temporal distribution of
different species during migration on the territory of
Relationship between the Intensity of Nocturnal Migration
Measured by Radar and the Anthropogenic Mortality of Birds
Boyan Michev1*, Pavel Zehtindjiev1, Martin P.Marinov1 & Felix Liechti2
1Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, 2 Gagarin Street, 1113 Soa, Bulgaria
2Swiss Ornithological Institute, CH-6204 Sempach, Switzerland
Abstract: Between August 27th and September 30th 2014 the intensity of nocturnal bird migration was measured in
the Dobrudzha Region (NE Bulgaria) using a specic bird radar. During the same time period and in the
same area (part of Natura 2000 net BGSPA0002051 Kaliakra and adjacent areas), road-kills as well as
collisions of birds with wind turbines were recorded. Along a 9-km-long secondary road, 95 dead birds
out of 24 species belonging to six orders were found. A systematic carcass search under 52 wind turbines
was examined and eight collision victims belonging to ve bird species of four orders were discovered.
The results did not show a relation between bird mortality due to wind turbine collisions and nocturnal
migration. However, a positive correlation between night passerine migration intensity and road mortality
of passerines was found. Windfarms do not appear to be more detrimental to migrating birds than other
anthropogenic sources of mortality, such as automobile trafc. The recorded high number of road-kills in
the designated Natura 2000 zone Kaliakra provides a basis for planning additional restrictions in this zone,
in order to secure the habitats, which are important for migrating passerine birds.
Key words: bird mortality, radar study, car trafc, wind turbines
Michev B., P. Zehtindjiev, M. P.Marinov & F. Liechti
Bulgaria (Zehtindjiev & whitfield 2010).
The growing demand for renewable energy
has led to the development of wind industry in
many parts of the world, including Bulgaria. A great
amount of actual information about bird migration
over the country was accumulated during the last ten
years as a result of demand for long-term ornitho-
logical data from the surroundings of planned wind
farms (michev et al. 2012; Zehtindjiev & whitfield
2012, 2013). With the development of wind energy
around the world, the question about the potential
risk of bird collisions with wind turbines and the
need of related studies has been raised (lArsen &
mAdsen 2000, lAngston & PullAn 2003, de lucAs
et al. 2007, BArrios & rodrígues 2007, michev et
al. 2012, Zehtindjiev & whitfield 2009, 2010, 2011,
2012, 2013, 2014).
The mortality of birds during migration has
never been related to the intensity of bird migra-
tion. Road infrastructure has been shown to exert
many negative effects on the populations of verte-
brates and ecosystems in general (smith & dodd
2003, vAn lAngevelde et al. 2009, wiAcek et al.
2015) and bird mortality due to collision with cars
is the most serious of them (erritZoe et al. 2003).
Bird trafc casualties are not systematically studied
in Bulgaria and data about the number of birds as
well as the composition of species among the col-
lision victims on the roads are scarce. The earliest
study of bird road-kill dynamics in Bulgaria has
been carried out by nAnkinov & todorov (1983).
The recent study of vAn der grift et al. (2008) and
kAmBourovA-ivAnovA еt al. (2012) has found a sig-
nicant impact of road trafc on the mortality of
birds, mammals, reptiles and amphibians. However,
no study on the relationship between the dynamics
of bird migration and bird mortality either due to
collisions with cars or with wind turbines has been
presented up to now.
Bulgaria has developed the National Network
of Natura 2000 sites and is currently planning man-
agement programs for these territories. The rate of
anthropogenic mortality of birds is of crucial sig-
nicance for the adequate and efcient planning
and implementation of research-grounded conser-
vation measures and policies in such protected ar-
eas as Natura 2000 zones. The present study was
partly carried out in Special Protection Area (SPA)
BG0002051 Kaliakra and the results from it could
be used for better management of this SPA zone.
The aim of the present study is to link for the
rst time the dynamics of nocturnal bird migration
and collision fatalities due to road trafc and wind
turbines in the same time period and on the same
territory. This will help to cast light on one of the
causes of bird mortality in typical habitats in the
north-eastern part of Bulgaria (South Dobrudzha).
Materials and Methods
The study was carried out between August 27th and
September 30th 2014 covering a total of 35 days, in-
cluding intervals of 315 hours with 3780 minutes ra-
dar scanning in the NE part of Bulgaria. The territory
consists mainly of arable land with different crops
(wheat, sunower, ax), intercepted with roads and
shelterbelts. The area also includes Ponto-Sarmatic
steppes designated as NATURA 2000 site Kaliakra
for protection of this unique habitat (Fig. 1).
Radar System
We used the Swiss BirdScan MS1 radar situated in
NE Bulgaria (43°26’51.52”N 28°27’12.48”E; Fig.
1). This xed pencil-beam radar system was devel-
oped especially for the study of bird migration by
the Swiss Ornithological Institute. The radar sys-
tem is based on 25 kW marine radar (Bridgemaster)
with wavelength of 3 cm (X-band radar). By using
a pencil-beam parabolic antenna (equivalent to the
Swiss tracking radar “Superedermaus”), the detec-
tion range is increased by about a factor of two, com-
pared to the standard T-bar antenna. The nominal an-
gle of the beam line is approximately 2.2° degrees.
The antenna can be set in various stationary eleva-
tions (hence “xed-beam” radar), with the following
The detection range is c. 4 km (for individual
small birds, e.g. chafnch) up to 7.5 km (for indi-
vidual larger birds, e.g. goose). Radar measurements
were continuously made during the night (20:00 h -
04:10 h EET) for the whole study period according
to the following scanning programs:
- Four minutes at an elevation angle of 1.7°
(equivalent to approximately 25-275 m elevation at
5 km distance);
- Four minutes at an elevation angle of
8.4°(equivalent to 675-825 m at 5 km distance);
- Four minutes at an elevation angle of 39.4°
(equivalent to 3375-3625 m at 5 km distance);
- This cycle was repeated every hour.
We used a tailor-made software (FixBeam) to
extract single echoes and distinguish (based on the
echo signature) birds or non-birds automatically
(ZAugg et al. 2008). Based on the wing beat pattern
of the bird extracted from the echo signature, ech-
oes were classied into ve different ight classes
according to Bruderer (1969, 1997): wader class;
passerine class; swift class; large single bird class
Relationship between the Intensity of Nocturnal Migration Measured by Radar and the Anthropogenic Mortality of Birds
and unknown class.
Using this data, we calculated the Migration
Trafc Rate (MTR = number of birds crossing a
hypothetic line of 1 km perpendicular to the mean
migratory direction for selected time – in our case
3 scannings x 4 minutes each hour at 3 altitude lay-
ers). This parameter was used to study the relation-
ship between the intensity of nocturnal migration
measured by radar and the anthropogenic mortality
of birds caused by car trafc and wind turbines.
Monitoring of bird mortality on the roads
A daily monitoring of bird mortality between August
28th and September 30th was conducted on the 9-
km-long stretch of a secondary road connecting
the villages Sveti Nikola and Tyulenovo, Kavarna
Municipality (Fig. 1). The monitoring was conduct-
ed by bicycle twice a day: in the morning between
7:00 and 8:00 AM EET and in the afternoon between
16:00 and 17:00 PM EET. All discovered corpses of
killed birds were identied and removed immedi-
ately to avoid double count. Information about date,
time, species, sex, age and location was collected.
Monitoring of collision fatalities with wind
Methodology developed for bird collision monitor-
ing at operational wind farms (morrison 1998) was
used. Plots measuring 200 x 200 m centered on a tur-
bine were searched on transects 20 m apart. The size
of these plots was based on the results of johnson et
al. (2000). The efciency and the adjusted mortality
were tested prior to carcass searches in the studied
area as recommended by morrison (1998).
It is well known that searches for victims of col-
lision with operational wind turbines fail to nd all
dead birds for several reasons. There are two principal
factors: search efciency (observer’s fail to discover
and register all dead birds) and removal/disappear-
ance of dead birds before the observer can potentially
nd them. Accounting for these two potential biases,
trials are typically undertaken in order to provide for
such correction. Trials of hen carcass searches and as-
sessment of its efciency in the studied territory were
done in 2009, 2010 and 2014 (Zehtindjiev & witfield
2009, 2010, 2014). According to these reports, the
efciency of the separate searches ranged 72-88%,
av. 79%. Carcass removal rate recorded in three au-
tumn seasons indicated that hen carcasses were not
removed very quickly after exposure, and several of
them persisted for longer than 10-14 days.
The implication of these results for the present
study is that most carcasses of collision victims and
‘naturally’ occurring carcasses probably persisted
(and so were available during the monitoring) for
longer time than the trial carcasses of hens. These
data allowed estimating the optimal frequency of
searches under turbines in respect to the time and
energy input in the period of study. The frequency
of seven days was estimated as optimal for adjusted
mortality calculation after several seasons of system-
atic studies in this territory and after several trials in
order to estimate the removal rate as well as searches
efciencies described in details in a number of re-
Fig.1. Map of the studied area
Michev B., P. Zehtindjiev, M. P.Marinov & F. Liechti
ports (Zehtindjiev & whitfield 2009, 2010, 2014).
Statistical methods
We examined whether the bird-vehicle collision
mortality of nocturnally migrating passerines was
related to their migration rate for a period of 34 days.
Only victims of order Passeriformes which migrate
during the night were included in the current analy-
sis (Table 3). We calculated the value of nocturnal
migration for each particular date as a sum of the
MTR measured between 8.00 PM EET on the pre-
vious date and 5.00 AM EET on the current date.
We calculated the Pearson’s correlation coefcient
between the MTR of the passerines and the number
of carcasses of nocturnally migrating passerines,
pairing each value of MTR for a given date with the
number of carcasses found on the same date. Prior
to analysis, data were transformed using Box-Cox
transformation procedure to meet assumptions of
normality. Data were analysed using Statistica 8
(Statsoft Inc., Tulsa, OK, USA).
Migration Trafc Rate (MTR)
Nocturnal migration during the studied period (27th
August - 30th September 2014) was dominated by
passerines and waders, while the other radar-classes
(swifts and large single birds) were rare. The radar
measurements showed up to four waves of nocturnal
migration during the study period (Fig. 2). The high-
est peak of 14% of all passed nocturnal migrants was
observed during the night of 29/30.08.2014.
Bird mortality caused by car trafc
The daily monitoring of road-kills revealed 95
dead birds of 24 species. Out of them, 89 individu-
als belonged to order Passeriformes and six indi-
viduals to orders Coraciiformes, Charadriiformes,
Falconiformes, Gruiformes and Pelecaniformes
(Table 1, Fig. 3). The Red-backed Shrike (Lanius
collurio), which is included in the Bird Directive
(2009/147/EC), represented the largest number of
dead birds. Also, more than ve victims were found
for House Sparrow/Spanish Sparrow (Passer domes-
ticus/Passer hispaniolensis) and Whinchat (Saxicola
rubetra). The temporal pattern of the road-kills is
presented on Fig. 4.
Bird mortality caused by wind generators
We recorded eight bird individuals of ve species
as collision victims in the course of monitoring 52
wind generators (Table 1). Only the Corn Crake
(Crex crex) is included in the Red Data Book of the
Republic of Bulgaria as Vulnerable and in Appendix
Fig. 2. Dynamics of passerine nocturnal migration, presented as proportion of all registered passerines during the
studied period
Fig. 3. Species composition and number (in ind. on the
X-axis) of the registered dead birds on a secondary road
in the study area. Dark grey columns – passerines, pale
grey columns – non-passerines, NIPB – non-identied
passerine bird
Relationship between the Intensity of Nocturnal Migration Measured by Radar and the Anthropogenic Mortality of Birds
1 of the Bird Directive (2009/147/EC). Taking into
account the conditions and assumptions described in
the methods and in accordance with the performed
experiments for the removal rate and efciency of
the searches, the estimated number of victims was
16 individuals in total.
Relation between bird mortality and Migration
Trafc Rate
The highest peak of passerine nocturnal migration,
registered on 29.08.2014, coincided with the high-
est peak of passerine road mortality. During the next
three days both parameters decreased simultane-
ously (Fig. 5). The number of nocturnally migrating
passerines killed on the road correlated signicantly
with the intensity of nocturnal passerine migration
estimated for the night preceding the road-kill moni-
toring (r = 0.36, R2 = 0.13, p = 0.037, n = 34).
The scarcity and lack of variability of the data
collected for migrating birds killed by collisions
with wind turbines during the studied period did not
allow us to nd any relationship with the nocturnal
migration of birds or with the road mortality (Table
2, Fig. 4).
In this study, we examined two anthropogenic sourc-
es of bird mortality in relation to autumn migration.
We found a signicant correlation between passerine
Table 1. Species composition and numbers of birds killed by vehicles and by turbines during the study period
Order Family Species Birds killed by
vehicles (n)
Birds killed by
turbines (n)
Apodiformes Apodidae Apus apus 0 1
Charadriiformes Laridae Larus michahellis 1 3
Coraciiformes Meropidae Merops apiaster 2 0
Falconiformes Falconidae Falco tinnunculus 1 0
Gruiformes Rallidae Crex crex 1 1
Passeriformes Alaudidae Alauda arvensis 0 2
Passeriformes Emberizidae Emberiza calandra 6 0
Passeriformes Hirundinidae Hirundo rustica 3 0
Passeriformes Hirundinidae Riparia riparia 1 0
Passeriformes Laniidae Lanius collurio 28 0
Passeriformes Laniidae Lanius minor 1 0
Passeriformes Motacillidae Motacilla alba 4 0
Passeriformes Motacillidae Motacilla ava 3 1
Passeriformes Muscicapidae Erithacus rubecula 2 0
Passeriformes Muscicapidae Luscinia luscinia 2 0
Passeriformes Muscicapidae Muscicapa striata 3 0
Passeriformes Muscicapidae Oenanthe isabellina 1 0
Passeriformes Muscicapidae Oenanthe isabellina/oenanthe 1 0
Passeriformes Muscicapidae Oenanthe oenanthe 2 0
Passeriformes Muscicapidae Phoenicurus ochruros 1 0
Passeriformes Muscicapidae Phoenicurus phoenicurus 1 0
Passeriformes Muscicapidae Saxicola rubetra 6 0
Passeriformes Muscicapidae Saxicola sp. 2 0
Passeriformes Passeridae Passer domesticus 4 0
Passeriformes Passeridae Passer domesticus/hispaniolensis 9 0
Passeriformes Phylloscopidae Phylloscopus trochilus 3 0
Passeriformes Sturnidae Sturnus vulgaris 2 0
Passeriformes Sylviidae Sylvia communis 1 0
Passeriformes NIPB* 3 0
Pelecaniformes Ardeidae Ardea cinerea 1 0
No orders: 7 No families: 16 No species: 26** 95 8
* NIPB – non-identied passerine bird.
** Bird corpses, whose species identity was not conrmed denitely, were excluded from this calculation.
Michev B., P. Zehtindjiev, M. P.Marinov & F. Liechti
migration rate and road-kill mortality of nocturnally
migrating passerines. However, the lower rate of
bird collisions with wind turbines did not allow us
to nd any relationship with the autumn migration.
The lack of nocturnal migrants among the victims
of wind turbines suggests that in the study area mi-
grating birds are much more vulnerable to anthropo-
genic impacts while feeding and resting than during
an active ight. Furthermore, the car trafc poses a
much greater threat than the wind turbines for either
migrating or non-migrating birds.
To the best of our knowledge, it is the rst re-
port of a signicant correlation between migration
intensities and road-kills. However, migration in-
tensity accounted for only 13% of variation in road
mortality – a result which is not surprising because
car trafc rate in the study area is highly heterogene-
ous unlike the regular mode of the radar measure-
ment. Many factors, such as vehicle velocity, bird
behaviour and feeding preferences, vegetation prox-
imity to the road etc., are probably linked to road
fatalities (de vAult et al. 2015, erritZoe et al. 2003,
nAnkinov & todorov 1983, sAntos et al. 2016).
The prevalence of passerines and the estab-
lished MTR in our study supports the results for
quantitative estimates of nocturnal migration over
the entire Balkan Peninsula (Zehtindjiev & liechti
2003). Based on the surveyed time interval, the peak
of the migrating passerines is most probably in the
end of August. The same dates (28-29 August) were
Table 2. Total number of Road Mortality and Turbine Mortality in the same territory of South Dobrudzha measured
simultaneously between 28th August and 30th September 2014
Date Road Mortality
Turbine Mortality
(n) Date Road Mortality
Turbine Mortality
28.8.2014 1 1 14.9.2014 3 2
29.8.2014 5 0 15.9.2014 2 0
30.8.2014 8 0 16.9.2014 3 0
31.8.2014 3 0 17.9.2014 1 0
1.9.2014 4 0 18.9.2014 1 0
2.9.2014 1 0 19.9.2014 2 0
3.9.2014 7 0 20.9.2014 5 0
4.9.2014 3 0 21.9.2014 5 0
5.9.2014 1 0 22.9.2014 2 0
6.9.2014 1 0 23.9.2014 1 1
7.9.2014 2 1 24.9.2014 1 0
8.9.2014 1 0 25.9.2014 3 0
9.9.2014 7 0 26.9.2014 1 0
10.9.2014 4 1 27.9.2014 0 1
11.9.2014 4 0 28.9.2014 0 0
12.9.2014 2 1 29.9.2014 4 0
13.9.2014 5 0 30.9.2014 1 0
Total 95 8
Fig. 4. Dynamics of total bird mortality (ind./day) on a 9-km-long secondary road segment (dashed line) and under 52
wind turbines (solid line) during the study period
Relationship between the Intensity of Nocturnal Migration Measured by Radar and the Anthropogenic Mortality of Birds
recorded by Zehtindjiev (2001b) for the territory of
Bulgaria. It is important to mention that the peak of
migration of the White Stork is also on these dates
(michev et al. 2011).
Our results show that bird mortality caused by
collisions with wind generators, adjusted by the ef-
ciency of the searches and removal rate, is com-
paratively low and does not correspond to the MTR
established by the radar in the same time period.
However, the collisions of nocturnal migrants with
cars are more frequent than wind turbine collisions
and therefore pose much greater threat for migrat-
ing birds in the study area. These results are con-
sistent with other studies from the USA, Canada
and Sweden where the annual estimation of bird
deaths due to collision with cars is hundreds of times
higher than bird mortality caused by wind turbines
(erickson et al. 2001, loss et al. 2015, rydell et
al. 2012). We suppose that the mortality rate differ-
ences in our results probably reect the differences
in location of the wind turbines and the studied road.
The wind turbines have been constructed in open
agricultural habitats crossed by shelterbelts (Fig. 1)
while the road segment studied for mortality spreads
along various habitats - agricultural elds, steppe
grassland, coppices, settlements and combinations
of them. Therefore, one can expect increased fatali-
ties because of the higher diversity and abundance of
bird species in close proximity to the road (nAnkinov
& todorov 1983, sAntos et al. 2016).
According to the species composition of the
road-kills, the red-backed shrike (Lanius collurio)
ranks rst, which may reect the fact that this spe-
cies is one of the most numerous among all night
migrants. In autumn the species migrates from the
end of August to the end of October (Zehtindjiev &
whitfield 2009, ivAnov 2011). The species compo-
sition of road-kills was similar to the species com-
position of nocturnal migration across this region
(Zehtindjiev & whitfield 2009), an additional evi-
dence that the number of victims reects the general
pattern of migration intensity.
The study was done in a region which covers
part of the designated Natura 2000 zone Kaliakra
and adjacent areas, therefore the obtained data can
be used in the management plans of this important
zone. The established number of birds killed by cars
indicates that the trafc should be considered as the
most important threat for migrating birds on this ter-
ritory and provides a basis for planning additional re-
strictions in this zone in order to secure the habitats,
which are important for migrating passerine birds.
The calculated number of around two birds per day
in a segment of 9 km of a secondary road reects in
7.7 birds per day for 35 km of the secondary roads
in total for the whole designated Natura 2000 zone
Kaliakra. To estimate this number, one should con-
sider at least two months of intensive bird migration,
Table 3. Number of nocturnally migrating passerines
killed on the road
Species Number
Lanius collurio 28
Lanius minor 1
Luscinia luscinia 2
Motacilla alba 4
Motacilla ava 3
Muscicapa striata 3
Oenanthe isabellina/oenanthe 4
Phoenicurus ochruros 1
Phoenicurus phoenicurus 1
Phylloscopus trochilus 3
Saxicola rubetra 8
Sylvia communis 1
Total 59
Fig. 5. Тrends of nocturnal passerine Migration Trafc Rate (MTR) and Road Mortality of nocturnally migrating pas-
serines during the studied period. Both variables are presented as proportions of the total passerine migration density
and the total number of nocturnally migrating passerines killed on the road, respectively. Solid line – nocturnal pas-
serine MTR, dashed line - Road Mortality of nocturnally migrating passerines
Michev B., P. Zehtindjiev, M. P.Marinov & F. Liechti
or 60 days with 462 birds killed only on the territory
of one Natura 2000 zone in NE Bulgaria. The num-
ber of the victims on the road in this important bird
area must be reduced by different measures, includ-
ing speed limits and wild bird crossing signs on all
secondary roads in the area.
Acknowledgments: We are grateful for the support and the kindly
supplied radar data by AES Geo Energy Sveti Nikola Wind Farm.
We are also grateful to the European Network for the Radar sur-
veillance of Animal Movement (ENRAM) for their valuable sup-
port and help. We thank Strahil Peev and Viktor Vasilev for their
help in collecting data, Baptiste Schmid for technical assistance,
Boyko Georgiev for the useful comments on the manuscript and
the anonymous reviewers for their useful comments.
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Received: 27.05.2016
Accepted: 13.10.2016
... 25% and 50% UD) of curlews during autumn and spring as well as for birds migrating at altitudes <250 and ≥250 m (see Fig. 3 intensity across the Baltic Sea at night and in the early morning, suggesting that night-time may be of particular concern, as has been found for songbirds (e.g. Michev et al., 2017). Because most curlews along the East Atlantic Flyway use the Wadden Sea as a wintering or stop-over site (Kleefstra et al., 2019), and curlews leaving the Wadden Sea during spring usually commence their migration during the evening , they are most likely to cross the Baltic Sea at night. ...
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Installation of offshore wind farms (OWFs) is becoming increasingly important to ensure a reduction in greenhouse gas emissions; however, OWFs also pose a threat to migrating birds and other wildlife. Informed marine spatial planning is therefore crucial, but individual‐based high‐resolution data on bird migration across the sea are currently lacking. We equipped 51 individuals of the near threatened Eurasian curlew Numenius arquata with GPS tags (118 flight tracks) across multiple years and countries to assess their four‐dimensional migration routes across the Baltic Sea (i.e. flight tracks, altitudes, phenology and diurnal patterns), to inform collision‐risk models and assess potential conflicts with current and future OWFs. Despite a broad‐front migration, we identified core migration areas in the south‐western Baltic Sea (and adjacent mainland), largely overlapping with already operating OWFs. Generalized linear models based on a resampling procedure to overcome autocorrelation of tracking data showed that flight altitudes across the sea and during autumn (median: 60 m) were significantly lower than those across land (median: 335 m) and during spring (median across sea: 150; median across land: 576 m). Across the sea, curlews spent 74.8% and 62.2% of their migration times below 300 m during autumn and spring, respectively, indicating a potentially high collision risk with OWFs. The mean flight speed was 56.3 km/h (±20.3 km/h). Migration intensity was highest at night over a 10‐day period during April, suggesting that restricted turbine operation for several days might be a possible management measure. Our study showed that, even for broad‐front migrants, it is possible to identify particularly sensitive sea areas deserving special protection enabling a sound marine spatial planning. This is a crucial finding also for various other shorebirds on the East Atlantic Flyway. Further studies are needed to assess the behavioural reactions of migrating birds with respect to OWFs using high‐resolution tracking data. Using a large long‐term international set of high‐resolution GPS‐tracking data, our study reveals the four‐dimensional nature of curlew migration against the background of ongoing installations of offshore wind farms (OWFs) in the Baltic Sea. We found that while curlews migrate across a wide band of the Baltic Sea, they had predictable high‐use flight areas that overlapped with OWFs, and flight altitude data showed that curlews were migrating across marine areas with OWFs at significantly lower altitudes than across the land, suggesting higher collision risk for offshore migrants regardless of time of day. Our results are important to inform collision risk models and ongoing marine spatial planning.
... It has been founded through the studies of Tanyo Michev in 1982 for studying the soaring birds along the Via Pontica bird flyway (MICHEV et al., 1987. Radar of the Bulgarian airports of Varna and Burgas were used for this kind of observations (MICHEV et al., 1987(MICHEV et al., , 2017(MICHEV et al., , 2020, NILSON et al. (2018), MICHEV (2021. Radar observations of migrations in the first years were combined with visual ones (MICHEV, 2021). ...
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A short review of the main achievement and the most eminent workers on the birdlife in Bulgaria in the last 277 years is presented. A total of 46 fields/ aspects of bird studies are outlined in brief. Each research field is described in short with quotation of the first, the major, the most important or the most popular publications. Full references of these publications are given. The bibliography of the great many of them appears transliterated/ translated from cyrilic alphabet for the first time. The total number of the ornithological publications of Bulgarian authors and these on the Bulgarian birds is estimated as ca. 8000. The present work lists full reference data for 1/ 12th of them (691 items). Georgi Hristovich (1863-1926) is the first Bulgarian ornithologist. The number of Bulgarian workers in ornithology permanently increased and in 2021 it overpasses 100 specialists, advanced birdwatchers and bird-conservation NGO-s collaborators. Ornithology in Bulgaria has data for 739 bird species (421 recent and 318 known from their fossil/ subfossil remains) in the country. Avifaunistic is the oldest and most developed field of ornithological researches, while pterylogy is the youngest and less elaborated of their aspects. The countries of the Balkan Peninsula are the most studied foreign territories of Bulgarian ornithological research. Antarctica is the most remoted region, where Bulgarian ornithologists made their field researches. They contributed to the exploration of the birdlife of 68 states and territories all over the World. A total of 40 new avian taxa have been described from Bulgaria – 1 recent (Streptopelia decaocto) and 39 fossil (Miocene – Early Holocene), an important contribution to the World avian science. The oldest and the largest avian collection are stored at the National Museum of Natural History at the Bulgarian Academy of Sciences in Sofia. This institution always was and at present is, the most influencing research center in ornithology of Bulgaria.
... Bats in particular showed a strong mortality peak during July-August. Natural history traits such as breeding and dispersal periods are known to influence temporal patterns in roadkill rates (Grilo et al., 2009); snakes tend to be more active with increased temperatures (Meek, 2009); high humidity and rainfall is typically associated with amphibians activity peaks and their breeding migrations (Semlitsch, 2008); birds that use roads as migration routes or due to juvenile dispersion (da Rosa & Bager, 2012), or have higher nocturnal migration rates, can also have higher roadkill rates (Michev et al., 2017). However, information on many of these traits are unknown for a wide range of species within our study area, and will be required to fully understand these patterns. ...
Road networks are increasing globally, and as such incur increased pressure on wildlife communities. Large-scale road expansion and infrastructure development occurring throughout Asia (i.e. Belt and Road Initiative) will affect hundreds of threatened species, leading to an increase in wildlife-vehicle collisions. However, only a limited number of studies have quantified road mortality within this threatened landscape. To rectify this, we monitored the spatial-temporal patterns of vertebrate roadkill in the Dong Phayayen-Khao Yai forest complex, an UNESCO World Heritage Site located in Thailand, considered a refuge for many globally threatened species. We ran 100 standardized road surveys between 2015 and 2017, on a 47.8-km highway transect currently being expanded, and recorded a total of 1395 casualties from 124 species. After correcting for removal time and detection probability, we estimated an average of 9688 vertebrate mortalities per year. We observed a mortality peak during the dry season for almost all taxonomic groups, due to a combination of high bird and bat mortality events. All taxa showed significant spatial clustering, highlighting high-risk road sections. We modelled the road and landscape features most likely to lead to higher mortality rates, disentangling small-scale (250-500 m from road) from large-scale effects (1000-2500 m). We recorded lower mortality rates and species diversity near forest sites in protected areas, representing either lower crossing events due to habitat quality or an already depleted environment. Spatial analyses provided information on hotspots and landscape factors, which can be used to inform future mitigations at multiple scales throughout the Southeast Asia region. Our study provides a baseline of the direct road impacts on vertebrate species in a tropical biodiversity hotspot, and we suggest that more studies be conducted to fully assess the direct road effects on the many threatened species in this landscape.
... For this reason, monitoring and understanding bird migration has gained interest across multiple fields of research. Assessing the hazard of collision with anthropogenic infrastructures (Aschwanden et al., 2018;Michev et al., 2017), predicting the effect of climate change (Both and Marvelde, 2007;Cox, 2010;Panuccio et al., 2016a;Saino et al., 2011) and the spread of avian diseases (Sullivan et al., 2018;van Toor et al., 2018), and estimating seed dispersal and other ecosystem services (Kleyheeg et al., 2019) are just some examples. ...
Hypatia-trackRadar is a Java standalone application designed to help biologists extract and process bird movement data from marine surveillance radars. This application integrates simultaneous collection of radar data and field observations by allowing the user to link information gathered from visual observers (such as bird species and flock size) to the radar echoes. A virtual transparent sheet positioned on the radar screen allows the user to visually follow and track the echoes on the radar screen. The application translates the position of the echoes on the screen in a metric coordinate system. Based on time and spatial position of the echoes the software automatically calculates multiple flight parameters, such as ground speed, track length and duration. We validated Hypatia-trackRadar using an unmanned aerial vehicle. Here we present the features of this application software and its first use in a real case study in a raptor migration bottleneck .
... Problem sections and regularities have been identified during the different annual seasons (see HANER et al., 2002;HELL et al., 2005;LODÉ, 2000;HUIJSER & BERGER, 2000;HAIGH, 2012;ROIG-MUNAR et al., 2012). In Bulgaria, identified problem areas with a concentration of road traffic casualties are reported by VAN DER GRIFT et al. (2008), data on road casualties in two types of road network give KAMBUROVA-IVANOVA et al. (2012), MOLLOV et al. (2013 and MICHEV et al. (2017). ...
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A total of 197 road kill victims were recorded in the period November 2015-May 2017 from the new section of the Maritsa Highway in South Bulgaria. The Northern White-breasted Hedgehog (Erinaceus roumanicus Barret-Hamilton, 1900)-18.6%, n=118, Eurasian Badger (Meles meles (Linnaeus, 1758))-16.9%, n=118, Golden Jackal (Canis aureus Linnaeus, 1758)-15.2%, n=118 and Common Buzzard (Buteo buteo (Linnaeus, 1758))-25.3%, n=79 were the most frequently observed victims. The number of victims detected at varying traffic intensities is different and increases with increasing road traffic. There are several parts of the highway where road kill victims are concentrated.
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In NE Bulgaria, AES Geo Energy OOD constructed a 156 MW wind farm consisting of 52 turbines: the St Nikola Wind Farm (SNWF). In autumn 2008, SNWF did not exist; in autumn 2009 the facility was built but not operational, and in the autumns of 2010, 2011, 2012 and 2013 SNWF was operational. SNWF is located approximately three to seven kilometers inland of the Black Sea coast and the cape Kaliakra. The SNWF area consists mainly of arable land involving small-scale cultivation of different crops, heavily intercepted with tracks and wooded shelter belts. Important Bird Areas (IBA) in Bulgaria are selected using an in-country standard for the site’s importance. IBA “Kaliakra” is designated as it is the only site in Bulgaria that keeps the remaining Eastern Dobrudzha steppe, as well as the biggest sea cliffs along the Bulgarian Black Sea Coast. The IBA is also designated as an important site for migrating birds along the Black sea coast (Via Pontica migration flyway). It is considered to be a bottle-neck migration site with annual aggregations of more than 29,000 storks, pelicans and cranes and more than 3,000 birds of prey. This study presents the comparative results of six autumn seasons at the SNWF, with a focus on the impacts on migrating birds. Data gathered from visual observations are analyzed. The data from the autumn monitoring in the years 2008 to 2013 are used to investigate the potential change in species composition, numbers, altitude or the flight direction of birds observed in these 6 years at SNWF. The variations in numbers of species, absolute number of birds, overall altitudes of flight and migratory direction of birds most sensitive to wind turbines do not indicate an adverse effect of the wind farm on diurnal migrating birds. The Turbine Shutdown System probably contributed to a reduced risk of collision during all years of operation within infrequent periods of intensive soaring bird migration and provided a safety mechanism to reduce collision risk for single birds and flocks of endangered bird species. The low number of victims of collision found during systematic searches for casualties under every turbine at an interval of 7 days or less in four autumn seasons does not provide evidence for additional mortality caused by SNWF that could be problematic to populations of any bird species migrating through the territory. The results to date indicate that SNWF does not constitute a significant obstacle or threat, either physically or demographically to any of the populations of diurnal autumn migrants observed in this study. The main results of the autumn monitoring of bird migration in the vicinity of SNWF in previous years are published at: The results of our study may contribute for the future understanding of cumulative impact of wind parks and habituation process in different bird species including thus with high conservation value.
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The first radar observations of bird migration in Bulgaria were carried out in the periods 25.08 - 13.10. 1982 and 22.08 - 8.10.1983 using the radar systems of Bourgas and Varna airports (radars Plessey with 4 ranges -15, 30, 60 and 120 km, wave lenght 10 cm and velocity of rotation 15 revolutions per minute). Radar research was pursued by visual observations, realised from Bourgas and Varna airports and neighbouring hills. As a results the routes of 341 flocks of soaring birds were traced of and put on maps (269 flocks of White Stork, 46 - of Great White Pelican, 13 - of Black Stork, 12 - of Common Crane etc) .
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Autumn nocturnal migration of waterbirds (Anseriformes and Charadriiformes) in North- Eastern Bulgaria. Results of a moon-watch study on flight direction and density of nocturnal migration of waders and waterfowl during 23 nights in autumn in NE Bulgaria are presented. Specific composition of possible nocturnal migrants is analysed. The seasonal changes in the mean flight direction of nocturnal migration were caused by differential passage of species with different wintering areas. The average density of nocturnal migration of waterbirds for the period of observations is presented. The moon-watch observations in autumn in the central part of the Lower Danube Plain revealed that nocturnal passage of waterfowl and waders goes along the general migration direction to the winter quarters, and not along the Danube river. Key words: Autumn, Balkan Peninsula, flight direction, migration density, migration traffic rate, moonwatch method, NE Bulgaria, seasonal changes.
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Understanding and reversing the widespread population declines of birds require estimating the magnitude of all mortality sources. Numerous anthropogenic mortality sources directly kill birds. Cause-specific annual mortality in the United States varies from billions (cat predation) to hundreds of millions (building and automobile collisions), tens of millions (power line collisions), millions (power line electrocutions, communication tower collisions), and hundreds of thousands (wind turbine collisions). However, great uncertainty exists about the independent and cumulative impacts of this mortality on avian populations. To facilitate this understanding, additional research is needed to estimate mortality for individual bird species and affected populations, to sample mortality throughout the annual cycle to inform full life-cycle population models, and to develop models that clarify the degree to which multiple mortality sources are additive or compensatory. We review sources of direct anthropogenic mortality in relation to the fundamental ecological objective of disentangling how mortality sources affect animal populations.
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The bird migration monitoring in the AES Geo Power Wind Park territory, Kaliakra region in autumn 2008
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Saint Nikola Wind Farm bird migration monitoring in autumn 2009
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Bird migration monitoring in the AES Geo Power Wind Park territory, Kaliakra region, in autumn 2011 and an evaluation of potential barrier effect after two years of operation
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Bird migration monitoring in the AES Geo Power Wind Park territory, Kaliakra region, in autumn 2012 and analisis of potential effect after 3 years of operation