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Acrocephalus 31 (145/146): 143−145, 2010
The Diet of a Lesser Spotted 
Eagle Aquila pomarina family in SE 
Bulgaria
Prehrana družine malega klinka~a Aquila 
pomarina v JV Bolgariji
Boyan Milchev¹, Dragan Chobanov² & Nikolay 
Tzankov³
 ¹  University of Forestry, Wildlife Management 
Department, Kl. Ochridski Blvd. 10, BG−1756 Sofia, 
Bulgaria, e−mail: boyan.m@abv.bg
 ²  Institute of Zoology, Tzar Osvoboditel 1, BG−1000 
Sofia, Bulgaria, e−mail: d_chobanov@hotmail.com
 ³  National Museum of Natural History, Tzar 
Osvoboditel 1, BG−1000 Sofia, Bulgaria,  
e−mail: n_tzankovbio@abv.bg
The diet of the Lesser Spotted Eagle Aquila pomarina 
during the breeding season predominantly includes 
small mammals, mainly voles Arvicolidae, followed 
by amphibians, small birds, and occasionally reptiles 
and large insects (Glutz von Blotzheim et al. 1971, 
Cramp 1980, del Hoyo et al. 1994). However, under 
the Mediterranean climate conditions, the diet can 
consist mainly of reptiles, followed by birds, insects 
and small mammals as demonstrated by a study 
carried out in Greece (Vlachos & Papageorgiou 
1996). The diet of this species in Bulgaria is generally 
unknown, with some available data only on the 
stomach contents of six specimens that included 
Common Vole Microtus arvalis, European Souslik 
Spermophilus citellus, unidentified lizard, Slow-worm 
Anguis fragilis and Marsh Frog Pelophylax ridibundus 
(Simeonov et al. 1991). Here we present data on 
the diet composition of a Lesser Spotted Eagle pair, 
breeding in SE Bulgaria that successfully raised its 
offspring twice, in 2000 and 2001.
The breeding territory of the studied Lesser Spotted 
Eagle pair is located close to the town of Burgas, SE 
Bulgaria (UTM NG39). It comprises Mandra Lake 
and the adjacent marshy area, the Izvorska river 
valley with arable lands, surrounded by low hills 
predominantly covered with dry pastures, wastelands 
and patches of oak forest. This region is situated in the 
Transitory Mediterranean Climate Zone (Galabov 
1982). The birds were not marked and occupied the 
same nest in the consecutive years. The distance from 
the nest to the forest edge was 100 m, measured by the 
GPS navigation device (Garmin eTrex Legend) and 
the computer software MapSource 6.11.6 (Garmin 
Ltd.). The percentage of major habitat types within 
the radius of 3 km around the nest, which corresponds 
to the mean activity range of the Lesser Spotted Eagle 
(Zub et al. 2010), were 77.4% open non-forest lands, 
10.6% forest, 8.9% wetlands and 3.1% urban lands 
(villages and main road networks). 
Pellets and food remains (single bones, skin, fur, 
feathers etc.) were collected from the nest and nearby 
resting places of adult birds during two visits per 
year, carried out in July and August 2000 and 2001. 
This corresponded to the second half of the breeding 
season (nestling period) and thus we minimized the 
possible negative impacts of the study on the breeding. 
The remains were identified by reference to our 
comparative collections kept in the National Museum 
of Natural History. Estimates of the minimum number 
of individuals (prey items, MNI) of vertebrates were 
based mainly on the remains of crania and cranial 
fragments, mandibles and pelvic bones, while the 
MNI of invertebrates was based on head fragments 
and mandibles. Difference in the number of prey 
items at the main animal group level in the two study 
years was tested using the χ² statistics. 
The Lesser Spotted Eagle diet composition was 
assessed on the basis of 110 prey items classified into 
27 different taxonomic categories (Table 1). The 
diet consisted of six main animal groups, among 
which small mammals (34.5%, range 25.4−46.8%) 
and insects (42.7%, range 27.7−54.0%) were most 
frequently identified in both years of the study. Far 
smaller was the share of reptiles, birds, amphibians 
and fish. Grasshopper Decticus albifrons (25.5%, 
range 17.0−31.7%) and vole Microtus arvalis / 
rossiaemeridionalis (21.8%, range 17.5−27.7%) were 
the most abundant species according to the number 
of prey items in our sample and the only ones that 
constituted over 10% of the total diet. 
In spite of prevalence of voles in the diet of Lesser 
Spotted Eagle throughout Europe, the latter did not 
predominate in the diet here as strongly as in the 
northern and more humid parts of the species’ range 
(Cramp 1980, del Hoyo et al. 1994). This was probably 
due to the fact that their numbers in SE Bulgaria are 
rather low (Straka & Gerasimov 1977), reflecting 
the opportunistic feeding habits of Lesser Spotted 
Eagle (Zub et al. 2010). Similarly, voles formed only 
28% prey items in the diet of Barn Owl Tyto alba, 
another species that largely preys upon voles, studied 
in the same area (Miltschev et al. 2004). The most 
numerous prey species, the adult grasshopper Decticus 
albifrons, is about 5 cm long and was also represented 
in considerable numbers in the diet of Black Storks 
144
B. Milchev, D. Chobanov & N. Tzankov: The Diet of a Lesser Spotted Eagle Aquila pomarina family in SE Bulgaria
Ciconia nigra (Miltschev et al. 2000) and Rose-
coloured Starlings Sturnus roseus (Miltschev & 
Tschobanov 2002) foraging in the same area. Given 
the fact that the studied eagle nest was situated close 
to the forest edge, our findings are in accordance with 
Table 1: Diet of a Lesser Spotted Eagle Aquila pomarina family, based on pellets and food remains, collected from the nest 
(nestling period) and nearby resting places of adult birds near Burgas (SE Bulgaria) in July and August, 2000 and 2001 (N – 
No. of prey items, % – percentage of prey items)
Tabela 1: Prehrana družine malega klinka~a Aquila pomarina, ugotovljena na podlagi izbljuvkov in ostankov hrane, zbranih na 
gnezdu (obdobje mladi~ev) in bližnjih po~ivali{~ih odraslih ptic pri Burgasu (JV Bolgarija) v juliju in avgustu 2000 in 2001 (N – 
{t. enot plena, % – odstotek enot plena)
Prey item (Taxon)/ 
Enota plena (Sistematska enota)
2000 2001 Total / Skupaj
N % N % N %
Erinaceus concolor 3 6.4 1 1.6 4 3.6
Talpa levantis 1 2.1 1 0.9
Neomys anomalus 1 1.6 1 0.9
Glis glis 1 2.1 1 0.9
Mus musculus / macedonicus 1 2.1 1 0.9
Sylvaemus flavicollis / sylvaticus 1 1.6 1 0.9
Microtus arvalis / rossiaemeridionalis 13 27.7 11 17.5 24 21.8
Rodentia spp. 3  6.4 2 3.2 5 4.5
Mammalia total / skupaj 22 46.8 16 25.4 38 34.5
Fringilla coelebs 1 1.6 1 0.9
Oscines spp. 4 8.5 1 1.6 5 4.5
Aves total / skupaj 4 8.5 2 3.2 6 5.5
Coluber caspius 2 4.3 2 3.2 4 3.6
Natrix tessellata 1 1.6 1 0.9
Natrix sp. 1 2.1 5 7.9 6 5.5
Lacerta viridis / trilineata 1 2.1 1 1.6 2 1.8
Reptilia total / skupaj 4 8.5 9 14.3 13 11.8
Pelophylax ridibunda 2 4.3 2 3.2 4 3.6
Amphibia subtotal 2 4.3 2 3.2 4 3.6
Carassius auratus 2 4.3 2 1.8
Pisces total / skupaj 2 4.3 2 1.8
Orthoptera
Decticus albifrons 8 17.0 20 31.7 28 25.5
Platycleis escalerai 1 1.6 1 0.9
Platycleis incerta / nigrosignata 3 6.4 1 1.6 4 3.6
Metrioptera roeselii / fedtschenkoi 2 3.2 2 1.8
Gryllotalpa sp. 1 1.6 1 0.9
Calliptamus italicus / barbarus 1 1.6 1 0.9
Coleoptera
Carabus coriaceus 2 3.2 2 1.8
Harpalus sp. 1 2.1 3 4.8 4 3.6
Aphodius sp. 2 3.2 2 1.8
Cetonia sp. 1 2.1 1 0.9
Cerambycidae 1 1.6 1 0.9
Insecta total / skupaj 13 27.7 34 54.0 47 42.7
Total / Skupaj 47 100.0 63 100.0 110 100.0
those of Zub et al. (2010) that Lesser Spotted Eagles 
nesting close to the forest edge and thus flying short 
distances between the nest and the hunting areas fed 
on smaller prey than birds nesting far from open non-
forest areas suitable for hunting.
145
Acrocephalus 31 (145/146): 143−145, 2010
The relatively high proportion of snakes of the 
genus Natrix probably reflects their high numbers in 
and around the wet zones in the hunting territory. 
They usually predominate in reptilian portion of the 
diet in both the northern and southern parts of the 
Lesser Spotted Eagle range (Cramp 1980, Vlachos 
& Papageorgiou 1996). Other main animal groups 
in the diet were merely supplementary. The remains 
of Goldfish Carassius auratus showed only heads 
with small fragments of the spinal column. These 
were rather taken accidentally − probably as carrion, 
reported as exceptional by Glutz von Blotzheim et 
al. (1971) and Cramp (1980). In spite of the presence 
of wetlands in the pair’s hunting territory, amphibians 
constituted only a small part of the diet. They are 
usually the second most important animal group in 
the diet of Lesser Spotted Eagle in Central and Eastern 
Europe, after small mammals (Glutz von Blotzheim 
et al. 1971). However, the amount of amphibians taken 
depends strongly on availability of voles. When vole 
populations are low, amphibians form up to 64% of 
the diet (Cramp 1980).
The difference in the proportion of the main six 
animal groups in the diet during the two consecutive 
years was statistically significant (χ²
5 
= 12.9, P = 
0.025). The increased taking of insects in 2001 was 
related to a significant reduction in the number of 
mammals in the diet composition. The feeding habits 
of Lesser Spotted Eagles are considered opportunistic 
(Zub et al. 2010). Changes in prey species numbers 
and its accessibility between years should be the 
reason for the considerable annual differences in the 
diet. However, there were no data available on the 
population dynamics of the potential prey species of 
Lesser Spotted Eagle in the study area to confirm this 
hypothesis.
Acknowledgements: We wish to thank N. Kodjabashev 
for the identification of the beetles. Thanks also to V. 
Georgiev and A. Kovachev for their assistance in the 
field.
Povzetek
Avtorji so v dveh gnezditvenih sezonah, v letih 2000 
in 2001, preu~evali prehrano družine malega klinka~a 
Aquila pomarina pri Burgasu (JV Bolgarija). Izbljuvke 
in ostanke hrane so v juliju in avgustu obeh let zbrali 
na gnezdu ter bližnjih po~ivali{~ih odraslih ptic, kar 
se je ~asovno ujemalo z drugo polovico gnezdenja 
(mladi~i v gnezdu). Sestavo prehrane so dolo~ili na 
podlagi 110 enot plena, ki so pripadale 27 razli~nim 
sistematskim enotam. Od glavnih živalskih skupin so 
v prehrani v obeh letih prevladovali mali sesalci (skupaj 
34,5 % enot plena) in žuželke (skupaj 42,7 % enot 
plena). Naj{tevil~nej{i vrsti sta bili kobilica primorska 
plenilka Decticus albifrons (25,5 %) in voluharica 
Microtus arvalis / rossiaemeridionalis (21,8 %). Razlika 
v {tevil~nosti {estih glavnih živalskih skupin med letoma 
raziskave je statisti~no zna~ilna. Ker je mali klinka~ 
prehranski oportunist, so razlike v sestavi prehrane 
med letoma verjetno posledica sprememb v {tevil~nosti 
posameznih vrst plena in njihove dostopnosti.
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Arrived / Prispelo: 7.7.2010
Accepted / Sprejeto: 22.6.2011