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10.2478/v10100-012-0008-6
A preliminary overview of raptor monitoring in Slovenia – an 
overview of methodologies, current monitoring status and future 
perspectives
Predhodni pregled monitoringa ptic roparic v Sloveniji – pregled metodologij, 
trenutnega stanja monitoringa in perspektive
Al Vrezec
National Institute of Biology, Večna pot 111, SI−1000 Ljubljana, Slovenia, e−mail: al.vrezec@nib.si
Slovenian Museum of Natural History, Prešernova 20, SI−1000 Ljubljana, Slovenia
Among 48 raptor species (birds of prey, owls, shrikes) recorded recently in 
Slovenia, some long-term monitoring activities are being conducted for more 
than half of them, mainly for conservation and research purposes. However, 
national coverage is achieved only in 15% of the species, whereas other 
monitoring programmes are more or less local. Two monitoring approaches are 
considered, the species specific approach and assemblage approach. Current 
ongoing monitoring programmes for raptors in Slovenia lack monitoring of 
breeding success, which is now confined to only a few owl species. Use of 
nestboxes should therefore be considered more broadly in the future for some 
species at least.
Key words: Slovenia, raptor monitoring, monitoring methodology, birds of 
prey, owls, shrikes
Ključne besede: Slovenija, monitoring ptic roparic, metodologija monitoringa, 
ujede, sove, srakoperji
1. Introduction
Despite a relatively long ornithological research 
tradition (Scopoli 1769) and certain conservation 
efforts for many raptor species in Slovenia (Beuk 
1920), the actual bird monitoring programmes 
and studies were embarked upon fairly recently, 
specifically in the 1980s. The aims of these monitoring 
programmes were quite different taking into account 
specific scientific (Tome 2009) or conservation based 
issues (Polak et al. 2004). They were designed either 
as broad international actions (Božič 2005) or as a way 
of bird popularization by monitoring of charismatic 
bird species (Denac, D. 2010). Therefore long-term 
data on bird or specifically raptor populations in 
Slovenia are of quite different quality and quantity 
based on species specific or assemblage-oriented 
surveys such as Farmland Bird Index counts (Kmecl & 
Figelj 2012). In terms of raptors, only few long-term 
monitoring results from Slovenia have been published 
(e.g. Denac 2003, Rubinić 2009, Tome 2009, 
Vrezec et al. 2009), leaving most of the collected data 
unanalysed and unpublished. 
The main aim of this study was therefore to 
inventory data collections in Slovenia appropriate for 
raptor monitoring purposes. I have taken into account 
the published and unpublished long-term data on 
population size (breeding and non-breeding) and 
breeding success, including survey methods overview, 
and identified strong and weak points of current 
monitoring programmes with future perspectives and 
needs. In the present preliminary overview of raptor 
monitoring in Slovenia, I have followed broader 
ecological definition of raptors including birds of prey, 
owls and shrikes.
2. Methods
For the purpose of this overview, an updated list of 
raptors recorded in Slovenia in the past 50 years was 
prepared. For each species the inventory of continuous 
or consecutive surveillances and especially long-term 
272
A. Vrezec: A preliminary overview of raptor monitoring in Slovenia – an overview of methodologies, current monitoring 
status and future perspectives
monitoring programmes was reviewed, taking into 
account the published data, unpublished reports, 
existing data bases or survey protocols.
3. Results and discussion
In the past 50 years, 49 raptor species have been 
recorded in Slovenia. Breeding has been confirmed 
for 27 of them (five species became recently extinct or 
breed irregularly or in very low numbers), at least 22 
species are regular migrants, and at least five species 
form regular wintering populations (Sovinc 1994, 
Geister 1995, Bordjan & Božič 2009, Hanžel & 
Šere 2011) (Table 1). From further analysis, 11 vagrant 
species have been excluded. For 71% of non-vagrant 
species, some long-term monitoring activities exist.
3.1. Monitoring schemes, data users
Monitoring of breeding populations was carried out 
for 58% of the breeders, but the actual breeding 
success was ascertained only for 27% of them. In 
raptor migration monitoring, 37% of the species were 
considered, and only 5% in wintering population 
monitoring (Table 1). However, the spatial coverage 
and time series differ greatly among species. 
The largest data set was obtained from regular 
ringing of migrating passerines (coordinated by the 
Slovenian Museum of Natural History) for the Red-
backed Shrike Lanius collurio, which started as early as 
in 1927, but systematically continued at a permanent 
bird ringing station in 1987 (Božič 2009, Šere 2009). 
Other monitoring programmes are much shorter and 
confined mainly to the last 20 years. They were mostly 
conducted by DOPPS - BirdLife Slovenia, Sečovlje 
Salina Nature Park and the National Institute of 
Biology for research, conservation and management 
purposes. 
Data users and monitoring programmes’ supporters 
are mainly governmental institutions from the field 
of nature conservation (Ministry of Agriculture and 
Environment, Institute of the Republic of Slovenia 
for Nature Conservation) and scientific research 
(Slovenian Research Agency, Ministry of Culture). 
Quite some monitoring efforts rely also on purely 
voluntary work. 
National coverage was achieved only in seven species 
(18%), mostly as breeding population monitoring. 
For 20 species (53%), the monitoring programmes 
were local (one or two sites). The latter were mainly 
migration monitoring programmes at specific sites, 
including monitoring of several migrating raptor 
species.
3.2. Monitoring methodology, key species and 
 key monitoring issues
Two monitoring approaches are considered in the 
scope of long-term data collection for raptors, species 
specific approach and assemblage approach. 
In the latter, raptors are target species of raptor 
migration monitoring, which is conducted at migration 
bottlenecks or other important migration sites, e.g. open 
wetlands, in Slovenia. Raptor migration monitoring has 
been conducted since 2005 on eight sites in Slovenia, 
but only on one more or less regularly within the 
scope of Natura 2000 network monitoring programme 
(Denac et al. 2010). This monitoring was conducted 
in spring and autumn and every raptor species was 
recorded, with Honey Buzzard Pernis apivorus, Griffon 
Vulture Gyps fulvus and Kestrel Falco tinnunculus as the 
most abundant raptors, the last two species as residents 
and not true migrants (Denac, K. 2010). 
Raptor migration is followed also within regular 
bird ringing programme coordinated by the Slovenian 
Museum of Natural History, but these data have not 
yet been fully evaluated for the monitoring purposes. 
Migration of raptors, mostly birds of prey, is 
Table 1: Overview of raptor monitoring in Slovenia (the number of species listed)
Tabela 1: Pregled monitoringa ptic roparic v Sloveniji (z navedenim {tevilom vrst)
Falconiformes Strigiformes Laniidae Total / Skupaj
No. of species 34 11 4 49
Breeders 15 9 3 27
Vagrants 10 1 0 11
Monitoring of breeding population 7 6 2 15
Monitoring of breeding success 2 5 1 8
Raptor migration monitoring 13 0 1 14
Monitoring of wintering population 1 0 1 2
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Acrocephalus 33 (154/155): 271−276, 2012
followed seasonally and annually also in the scope 
of waterbird counts at larger wetlands in Slovenia. 
This has been regularly conducted since 2002 (since 
1983 at only one site) on at least five sites, in which 
migrating as well as breeding and wintering raptor 
populations are considered, with Marsh Harrier Circus 
aeruginosus, Buzzard Buteo buteo, Red-footed Falcon 
F. vespertinus, Kestrel and Osprey Pandion haliaetus as 
the most abundant species (Bordjan & Božič 2009, 
Škornik 2009, Bordjan 2012). For the White-tailed 
Eagle Haliaeetus albicilla, the usefulness of large scale 
and non-targeted data from International Waterbird 
Census (IWC) counts has been shown. In Slovenia, the 
IWC has been continuously conducted on almost all 
water bodies since 1997 (Štumberger 1997). Despite 
winter counts, this survey appeared to be very useful 
for estimating breeding population trends of the 
White-tailed Eagle (Vrezec et al. 2009). An increase 
in winter population (estimated with TRIM software) 
corresponded very well to the increase of new nests 
found. 
Breeding population of some species is followed 
in consecutive periods, although not annually, for 
example for the Red-backed Shrike, where local 
population is surveyed approximately every five years 
(Denac 2003). Since 2007, breeding populations of 
some common raptors, e.g. Kestrel and Red-backed 
Shrike, have been followed by annual bird surveys 
conducted on 102 plots over the country as part of 
the Farmland Bird Index programme, conducted by 
DOPPS - BirdLife Slovenia (Kmecl & Figelj 2012). 
Collection of biological material (carcasses, eggs, 
feathers etc.) that might be an important source 
for with raptor monitoring, i.e. monitoring of 
contaminants in raptor tissues, is conducted by the 
Slovenian Museum of Natural History, but with no 
specific collection programme for raptors so far.
The species specific monitoring programmes 
are focused mainly on breeders (Table 2), with the 
exception of the Great Grey Shrike L. excubitor for 
which regular surveys of its winter numbers have 
been conducted since 2000, currently on two larger 
open areas in Slovenia at least, using the area count 
method (Bombek 2001). Some endangered raptor 
species have been included in the national monitoring 
scheme of qualification species of the Natura 2000 
network: Lesser Spotted Eagle Aquila pomarina, 
Peregrine Falcon F. peregrinus, Scops Owl Otus scops, 
Eagle Owl Bubo bubo, Ural Owl Strix uralensis and 
Lesser Grey Shrike L. minor (Rubinić 2009, Denac 
et al. 2010). However, the species specific monitoring 
programmes are focused mostly on territorial pair 
counts or chick presence in the nest at most, but 
rarely on other breeding and ecological parameters 
(Table 2). These were part of more detailed but local 
studies of feeding and breeding ecology in raptors (i.e. 
Long-eared Owl Asio otus, Tome 2003 & 2009) or 
research nestbox programme (i.e. Tawny S. aluco and 
Ural Owl, Vrezec 2007 & unpubl.).
Many monitoring programmes in Slovenia are 
part of a broad international cooperation, especially 
with BirdLife International. Migration monitoring 
was designed in cooperation with Austrian and Italian 
researchers (Mihelič & Genero 2005, Probst 
2010), whereas species specific monitoring of owls 
was developed in close cooperation with Finnish, 
Croatian, Italian, Austrian and some other researchers 
(e.g. Vrezec & Tutiš 2003). Currently, there is a 
bilateral project with Bosnia and Herzegovina going 
on, aimed at joint study of some owl species.
3.3. Strengths and weaknesses of current 
 monitoring programmes, future perspectives
Monitoring programmes should be cost-effective 
(McDonald-Madden et al. 2010) to ensure long-
term surveillance according to limited financial and 
human resources on one hand and its information 
efficiency on the other, which includes large scale 
and complex survey approach. Since raptors are 
charismatic and usually well known species, it is 
important to search for possibilities at least for 
their population monitoring in current ongoing 
monitoring programmes, e.g. population monitoring 
of the White-tailed Eagle in Slovenia (Vrezec et al. 
2009). In Slovenia, however, nearly a half of raptor 
species are currently not covered by any monitoring 
programme or only migrating population is 
monitored, while their breeding populations have not 
been taken into consideration. 
In Slovenia, monitoring of raptors’ breeding success 
is currently confined to just few owl species (Table 
2). The use of nestboxes is still underrepresented in 
raptor monitoring and research (Lambrechts et al. 
2012) and should be more broadly used. In general, 
the conservation needs for nestboxes in order to 
supplement nest sites for hole nesting raptors are low 
due to still well preserved forest stands in Slovenia, 
which provide enough natural possibilities for 
breeding. Currently, nestboxes are used for Kestrel, 
Barn Owl Tyto alba, Scops Owl, Tawny Owl, Ural 
Owl, Tengmalm’s owl Aegolius funereus and Little 
Owl Athene noctua, although mostly at the local level 
with low quantity and different success. However, 
the perspective of nestbox application in monitoring 
programmes is to recruit volunteers to maintain 
274
A. Vrezec: A preliminary overview of raptor monitoring in Slovenia – an overview of methodologies, current monitoring 
status and future perspectives
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Acrocephalus 33 (154/155): 271−276, 2012
different kinds of nestboxes for raptors. Based on 
Finnish raptor monitoring programme (Saurola 
2008), this provides good population as well as 
breeding success monitoring. 
In order to explain monitoring results, some key 
environmental parameters should be included in the 
monitoring programmes, which are considered in 
Slovenia only marginally for research needs (e.g. Tome 
2009). Especially, there is a need for monitoring of 
threats, which have been studied in Slovenia only 
preliminary, e.g. roadkill (Rubinič & Vrezec 2001) 
and electrocution (Rubinić 2009), but not followed 
by a long-term scheme and connected to population 
monitoring programmes.
The future perspectives of monitoring for raptors 
in Slovenia, largely stimulated by EURAPMON, are: 
(1) to collect current scattered data and to produce 
reliable national trends where possible, (2) to develop 
efficient field methods (survey, breeding success), (3) 
to start with nestboxes programme at the national level 
(volunteer-based), (4) to include ringing activity and 
advanced telemetry studies into raptor monitoring, 
(5) to include mortality monitoring or monitoring 
of threats, and (6) to start with systematic biological 
material collection of raptors for the purposes of 
monitoring with raptors. These issues should be largely 
enhanced by international cooperation at the point of 
general monitoring scheme establishment.
Acknowledgements: To accomplish this overview, 
several colleagues offered me great help in obtaining 
additional information on unpublished but ongoing 
monitoring programmes for raptors in Slovenia: 
Dominik Bombek, Dejan Bordjan, Katarina Denac, 
Dare Fekonja, Dr Primož Kmecelj, Dr Urša Koce, 
Tomaž Mihelič and Dr Davorin Tome.
4. Povzetek
Dolgoročni monitoring trenutno poteka za dobro 
polovico od 48 ptic roparic (ujed, sov, srakoperjev), 
zabeleženih v zadnjem obdobju v Sloveniji, predvsem 
za potrebe varstva in raziskovanja teh ptic. Vendar pa je 
na nacionalni ravni pokritih le 15 % vrst, medtem ko 
drugi programi monitoringa potekajo bolj ali manj na 
lokalno. V rabi sta dva pristopa monitoringa, in sicer 
vrstno specifični pristop in pristop na ravni združb. 
Sedanji programi monitoringa za ptice roparice v 
Sloveniji pa ne zajemajo monitoringa njihovega 
gnezditvenega uspeha, ki je trenutno omejen le na 
sove. V prihodnosti bi za nadaljnji razvoj monitoronga 
ptic roparic v Sloveniji morali razmisliti predvsem 
o: (1) zbiranju obstoječih a razpršenih podatkov, s 
katerimi bi lahko izračunali zanesljive populacijske 
trende vsaj za nekatere vrste, (2) razvoju učinkovitih 
terenskih metod (popisi, ugotavljanje gnezditvenega 
uspeha), (3) začetku programa z uporabo gnezdilnic 
na nacionalnem nivoju (s širšim vključevanjem 
prostovoljcev), (4) vključitvi obročkovalske 
aktivnosti in uporabe naprednih telemetrijskih 
tehnik v monitoring ptic roparic, (5) vključitvi 
monitoringa smrtnosti in dejavnikov ogrožanja v 
sheme monitoringa in (6) začetku sistematičnega 
zbiranja biološkega materiala ptic roparic za namene 
monitoringa onesnažil in strupov. Ti cilji morajo 
biti tesno povezani z mednarodnim sodelovanjem za 
postavitev nacionalne sheme monitoringa za ptice 
roparice v Sloveniji.
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International Symposium Dornbirn 2003. – Dornbirn.
Arrived / Prispelo: 27. 3. 2013
Accepted / Sprejeto: 1. 7. 2013