Increase of the Population of the Eastern Imperial Eagle (Aquila Heliaca) in Bulgaria

ACTA ZOOLOGICA BULGARICA Acta zool. bulg., Suppl. 3, 2011: 41-54

Increase of the Population of the Eastern Imperial Eagle (Aquila heliaca) in Bulgaria

Dimitar A. Demerdzhiev1, Gradimir Zh. Gradev2, Stoycho A. Stoychev3, Ivelin I. Ivanov4, Tzeno Hr. Petrov5 and Simeon A. Marin4

1 31 Bulgaria Blvd., 4230 Asenovgrad, Bulgaria; E-mail: [email protected]; www.bspb.org; www.saveraptors.org 2 Green Balkans NGO; 160, Shesty Septemvry Blvd., Plovdiv 4000, Bulgaria; E-mail: [email protected] 3 BSPB/BirdLife Bulgaria; Haskovo 6300, P.O.Box 130, Bulgaria; e-mail: [email protected]; www.bspb.org 4 Green Balkans NGO; 9, Stara Planina Str., Stara Zagora 6000, Bulgaria; E-mails: [email protected]; [email protected] 5 3 Nikola Vapcarov Str., Asenovgrad, Bulgaria; E-mail: [email protected], www.bspb.org

Abstract: Since 2000, the systematic conservation activities have resulted in an improved status of the Bulgarian population of Eastern Imperial Eagle (Aquila heliaca Sa v ign y 1809). The population is estimated at 25-30 pairs. In the period 2001-2009, 13 newly occupied and 3 reoccupied territories were recorded. In 2009 the number of known occupied territories increased to�� 20. �O��ccu��pie�d�� territories, bree�d��ing pairs, an�d�� pop�u��la� tion breeding parameters were recorded on annual basis. The recorded data included adult survival rate and age structure of the breeding population. The ��a�v�erage�� v�al��u�es�� of the breed�ing�� parameters of the popu�� lation for the period 2000-2009 were as follows: productivity 0.90±0.23; breeding success 1.01±0.26; fledglings success 1.56±0.25; and success rate 64.45% ±11.52. Nest guarding, rehabilitation of injured birds and subsequent release, “moving of pairs”, supplementary feeding, construction of artifiial nests, increase of the awareness among local communities and authorities, nesting habitat management, ringing of nestlings, satellite and radio tracking, and purchase of land around the nests have been implemented for the conservation of the species. The main threats are: habitat loss, disturbance, shooting, poisoning, and natural disasters.

Key words: population growth, Eastern Imperial Eagle, conservation, breeding parameters, Bulgaria

Introduction

The Eastern Imperial Eagle is�� c��lassi�f��e�d as ��vu��lner� 2002, Ho r v a th et al. 2002, Ho r v a th et al. 2011, able on a global scale (IUCN 2009) and threatened Da n k o et al. 2011, Wich m a nn 2011, Ve t r o v , at European level (Tuc k e r , He a th 1994). The species Mi l o b o g 2008). is listed in Annex I of the Birds Directive, Appendix At the end of the 19th and the beginning of the I of CITES, and Appendix II of the Bonn and Bern 20th centuries the species was abundant and wide- Conventions. At national level, the species is included spread throughout the country (Fa r m a n 1869, in Annexes II and III of the Biological Diversity Act, as El w e s , Buc k l e y 1870, Ra d a k o ff 1879, Al l e o n well as in the Red Data Book of Bulgaria (in press). 1886, Hr i s t o v ich 1890, Re i s e r 1894, Le v e r k uhn Increased numbers of Eastern Imperial Eagles 1907). The subsequent period of signifiant decline were reported in various parts of the species’ range of the Eastern Imperial Eagle population turned the (Ka r y a k in 1998, 1999, 2008, Ka r y a k in et al. 2008, species into one of Bulgaria’s rarest birds (Pa t e v Be l i k , Ga l u s hin 1999, Be l i k 2008, Ba g y u r a et al. 1950). Mich e v , Pe t r o v (1979) ��reporte� the o��ccu�r�

41 Demerdzhiev D., G. Gradev, S. Stoychev, I. Ivanov, T. Petrov and S. Marin rence of the species in 19 localities in the country for One hundred and twenty-fie 10x10 km UTM the period 1970-1978. Between 1980 and 1993 the grid squares in the areas harboring breeding Eastern species was reported in 35 localities; however, there Imperial Eagles were inspected every year or once were only nine cases of confrmed breeding (Pe t r o v every ��two�� years�� sear��c�hing�� for�� newly�� o��ccu��pie�d�� ter� et al. 1996). F�or�� that period� ��the popu�lation�� was es� ritories. In addition, 150 UTM grid squares, where timated at 15-20 breeding pairs. With the intensifed the species was recorded during the breeding sea� ornithological �� resear�ch after 1990 an�� the�� consist�� son with varying degrees of reliability of breeding, ent ��st��ud��ying ��of�� the ��Eastern Imperial ��Eagle ��d��istrib��u� or which represent suitable habitats, were visited at tion, threats, and numbers during the period 1994- least once during the period�� 200�0��-��200��9��. ��The ��inspec�� 2002 (St o y ch e v 1997, Pe t r o v 1999), the number tions involved transect methods used mainly along of known pairs reached 13. For the same period the river valleys or streams, or examination of high and/ population was estimated at 20-25 pairs (St o y ch e v or single trees in open habitats. Another method used et al. 2004) and 30-40 pairs (Na n k in o v et al. 2004). during the inspections was observations from view If a population of large and long-lived raptors is point (Bibb y et al. 1999, Аnd e r s e n 2007). ��The ��st��ud� to grow, it must have high survival rates of adult and ies were carried out mainly in the period February- subadult ��in��d�i�v�i�du��als��,�� presen��c�e of floatersfl oaters,,�� goo�� good� ��breed�� May, when trees were not in full leaf and the nests ing success,�� a�v�ailability�� of su�itable�� habitats �c��ompris� could easily be seen. Observations were also carried ing breeding ��an��d�� foraging�� sites��,�� age�� of�� f��rst�� repro��duc� out in June and July, monitoring the eagles’ behavior tion and maturity, and mitigation of major limiting in order to locate their nests. The degree of certainty factors (Ne wt o n 1979, Ka t z n e r et al. 2006). of breeding is according to Ha g e m e j e r , Bl a i r 1997. The systematic research implemented over the During�� the ��bree�d��ing ��perio�d�� (��F��ebr�u��ary�-�A�u�g�u��st��)�� mon� past decade revealed an obvious increase in the Eastern itoring of occupied nests was carried out twice or Imperial Eagle population in Bulgaria.�� Newly�� o��ccu� three times a month. During the autumn and winter pied�� territories�� were�� re��c�or��d�e�d�� in�� hilly�� an��d�� lowlan��d�� ar�� period the breeding territory of each pair was visited eas of the Sakar and the Western Strandja Mountains at least once a month.�� Risky ��nests�� sit�u��ate�d�� near ��ar� as well as the ��T��u�n�d��ja ri�v��er �v��alley, while loss of ter� able ��lan��d��s ��or�� roa��d��s�� were�� g��u��ar�d�e�d�� du��ring ��the�� bree��d� ritories was recorded in the mountain areas (Hr i s t o v , ing season by volunteers of the two organizations to St o y n o v 2002, De m e r d z hi e v 2004, De m e r d z hi e v increase the breeding success. In cases when a pair m a nu s c r ipt , Ang e l o v 2009). The species’ population bred in an unsuitable place, where the chances of is estimated at 25-30 pairs, as 20 breeding territories raising chicks were poor, the access to the nest was occupied by pairs were known in 2009. hindered so that birds could not alight on the nest. Data analyses Material and Methods Occupied territories, breeding pairs, and population breeding parameters were recorded on an annual ba� Field surveys sis. The recorded data included adult survival rate Since 20002000,, the researc�h and� � �c��onser�vation a�c��ti�v�i� and�� age ��str��uc��t�u�re�� of�� the ��bree�d��ing ��pop�u��lation. The es� ties implemented by the Bulgarian Society for the timates of the annual mortality of breeders (adult and Protection of Birds and Green Balkans NGO have subadult) were based on the replacement of birds in improved the status of the Eastern Imperial Eagle pairs. The new partner is considered to replace a in Bulgaria. The intensity of the monitoring and the dead mate.�� Howe�v��er,�� this�� assessment�� is�� not�� an�� abso�� quality ��of�� the ��gathere�d� �d��ata ��were impro�v�e�d��, th�u��s i�d��en� lute ��v��al�u��e ��du��e ��to�� the�� fa��c�t�� that�� sometimes�� it is impos� tifying the dynamics of the species’ population. The sible to record the replacement of a partner from the systematic regional studies carried out by the experts pair by an individual of the same age (Fe r r e r 2001). of these two organizations every year minimized the Breeding Eastern Imperial Eagles fo��u�n�d�� d� ea��d� � du��r�� risk of leaving territories occupied by eagles unde� ing the study period were also reported��. ��The i�d��enti� tected. This method makes it possible to record the fiation of plumage is according to Fo r s m a n (2005). actual situation of the population (Ne wt o n 1979). Considering the different opinions regarding the

42 Increase of the Population of the Eastern Imperial Eagle (Aquila heliaca) in Bulgaria number of plumages of the Imperial Eagle (Cl a r k vere decline, and by the end of 1970s there were 2004, Fo r s m a n 2005), and the vaguely determined only 3 certain localities of this species situated in marks of the last, sixth plumage by Fo r s m a n (2005), mountain areas of 400 m to 1.200 m a.s.l. (Mich e v , the birds at that age (6th calendar year�)�� were �c��onsi��d� Pe t r o v 1979). The gradual recovery of the Imperial ered adults.�� The ��pairs ��were ��d�i�v�i�d�e�d�� into ��three ��cate�� Eagle population in Bulgaria began after the socio- gories: adult – consisting of two individuals in adult economic changes and the adoption of extensive plumage;�� mixe�d�� –� �c��onsisting ��of�� an ��in�d�i�v�i��du��al ��in ��im� agricultural practices in the 1990s. The species is mature plumage (second-ffth) and an adult partner distributed mainly in SE Bulgaria. Since the 1960s, (from sixth plumage up); and immature – consisting there has been no confrmed breeding of this species of two individuals in immature plumage. in northern Bulgaria. In the period 2000-2009 there We estimated the productivity (number of were 25 known breeding territories occupied over fledglings per occupied territory)��,�� the bree�d��ing s��uc� the years by 24 pairs1 (Fig. 1). cess (number of fledglings per breeding pair), and The area with the greatest number of nests is the fledglings success (number of fledglings per suc� the Sakar Mountains and the lower reaches of the cessful pair) for the period 2000-2009, including 148 Maritsa River, harboring 1��1�� known nests. The habi� breeding attempts. For the period 2000-2009, we also tat of the pairs (n = 8) breeding in the Southern Sakar estimated the value of the success rate (frequency of Mountains is represente� by some 40% of aban� breeding attempts with at least one fledged chick), doned areas, grasslands, signifiant overgrowth of including 132 breeding attempts. scrubs and small trees, midsized pastures and forests, Statistic�� pro�c��essing ��of� �d��ata ��was �c��arrie�d�� o�u��t �u�s� 50-250 m a.s.l.. In the Northern Sakar Mountains, ing the program Statistica for Windows, Release the ��three�� bree��d��ing ��pairs�� are�� fo�u�n�d�� in�� habitats �char�� 7.0 (STATSOFT Inc . 1984-2004). The comparison acterize� by some 40% of aban�d��one� areas or ar� of the breeding parameters was based on the para� able lands, signifiant representation of pastures metric One-way АNOVA analysis with post-hoc and vineyards and some scrub patches, 100-250 m LSD-test. In the analysis, the breeding pairs were a.s.l.. The area with the second greatest number of presented in groups based on the geographical nests is the neighboring hilly region of the Dervent regions, corresponding almost entirely to their Heights – Western Strandzha, where 5 confrmed habitat preferences. Тhe two pairs in Sredna Gora breeding pairs were recorded. The terrains used by and the only pair in the Eastern Rhodopes were unit� Imperial Eagles breeding in this area�� are�� character�� ed in one group (mountain-wooded region) due to ized�� by�� more�� than�� 50 ��%�� of�� aband�one��d�� areas��,�� insig�� nifiant representation of pastures and grasslands, the similarity in their habitats (D�e m e rd Dz hi H Ie v � m a Nnu U �- and a low percentage of forest coverage, 250-280 m s c r ipt ).�� The ��d��ata ��was�� analyze�d�� for�� normal ��d��istrib��u� tion through the Shapiro-Wilk test (SHAPIRO et al., a.s.l. To the north of these pairs, in the Tundja river 1968). Results with p<0.05 [α=5%] were considered valley, fie breeding pairs are recorded, situated in signifiant. lowlands or low hilly treeless areas, between 130- 250�� m�� a.s.l. ��The habitats �c��onsist of abo�u��t ��70% of�� ar� able lands and abandoned areas, small pastures and Results grasslands��, agri��cu��lt��u�ral�� c�rops,�� and� ��insignifi��ant rep� resentation of tree-bush vegetation.�� The ��pairs ��bree��d� Breeding distribution and habitat performance ing in these regions, constituting 87.5% of all known At the end of the 19th and the beginning of the 20th pairs, could be considered as a subpopulation of the centuries the species was reported by many au� species (St o y ch e v et al. 2004). A breeding group, thors as abundant and wide-spread (Fa r m a n 1869, consisting of only 2 breeding pairs, was located in El w e s , Buc k l e y 1870, Ra d a k o ff 1879, Al l e o n the Sredna Gora Mountains. There was one breeding 1886, Hr i s t o v ich 1890, Re i s e r 1894, Le v e r k uhn territory known in the Eastern Rhodope Mountains, 1907). During the following decades the Eastern probably remaining from a disappearing breeding Imperial ��Eagle ��pop�u��lation ��in ��B�u��lgaria ��s�u��ffere�d�� se� group of Imperial Eagles (Hr i s t o v , St o y n o v 2002,

1 One of the breeding pairs occupied two different territories over the years.

43 Demerdzhiev D., G. Gradev, S. Stoychev, I. Ivanov, T. Petrov and S. Marin

Fig. 1. Distribution of the occupied breeding territories in the periods 1990-1999 (A) and 2000-2009 (В); ● – one nest; ▲ – two nests

44 Increase of the Population of the Eastern Imperial Eagle (Aquila heliaca) in Bulgaria

De m e r d z hi e v 2004, De m e r d z hi e v manuscript). The Annual survival rate of breeders varied from Imperial Eagles breeding in these two mountains be� 0��.��875 ��to ��1. ��As a whole, the s�u�r�v�i�v��al rate of bree��d� long to the mountain-wooded habitat, characterized ers ±SD for the period 2000-2009 was 0.954±0.039. by 30% to 70% of forests, agricultural crops, and The survival rates of breeders were found to be not low representation of abandoned areas and pastures, dependent on the sex of the bird. The�� ann��u��al ��mortal�� 330-1.100 m a.s.l. ity of breeders of the Imperial Eagle population in There were also observations of single birds and Bulgaria varied from 0 to 12.5%, i.e. an average of pairs in northern Bulgaria, the Western Rhodopes, 4.56% ±3.92 for the study period. and the Western Balkan Mountains, but breeding Estimation of the mean value of productivity, was not proven (St o y ch e v et al. 2007). For the pe� breeding success, ��an�d flfle �ed��glings s��ucc��ess for the pe� riod 2000-2009, there were 24 cases of certain, three riod 2000-2009, including 148 breeding attempts, is of probable, and six of possible breeding. presented in Table 1. Based on this data, the Bulgarian population In general, the a�v��erage �v��al�ues of the bree��d� for the period 2002-2009 was estimated at 25-30 ing parameters of the Eastern Imperial Eagle pop� breeding pairs. ulation for the period 2000-2009 were as follows: Occupation of new breeding territories by Productivity (P) 0.90±0.23; Breeding Success (BS) Imperial Eagles was recorded after 2001. The number 1.01±0.26; and Fledglings Success (FS) 1.56±0.25. of territories occupied by pairs increased from 8 to The dynamics of the breeding parameters over the 20 between 2000 and 2009 (Fig. 2). years was monitored as well (Fig. 3). The lowest values of the breeding success were Breeding parameters recorded in 2003, when the percentage of immature During the perio� 20020000��-�2009��2009,��, 63 �d ��ifferent ter� breeders was highest (Fig. 4). Maximum values of ritorial individuals, of which 13 replacements and 2 breeding success were recorded in 2005, 1.58. discovered dead breeders, were recorded in 25 occu� The success rate varied from 44.4% to 80%, i.e. pied territories. In two other cases, the replacement a mean value of 64.45% ±11.52. of a partner was not related to a dead mate, because Comparing the breeding parameters of Eastern it was recorded that the newcomer had displaced the Imperial Eagles breeding in different regions, statis� previous breeder (De m e r d z hi e v m a nu s c r ipt ). These tically signifiant differences (��p��<��0.05�)�� were i�d��enti� two cases were excluded from the mortality analysis. fed in productivity, breeding success, and fledglings

Number of territories occupied by pairs Number of pairs s tart incubating 25

20 s

r 15 i a P 10

0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

Years

Fig. 2. Eastern Imperial Eagle population dynamics in Bulgaria

45 Demerdzhiev D., G. Gradev, S. Stoychev, I. Ivanov, T. Petrov and S. Marin

Table 1. Descriptive statistics of breeding parameters. P = Productivity; BS = Breeding Success; FS = Fledglings Suc� cess.

Sum Mean Error Valid N Valid Std.Dev. Variable Standard -95,000% Minimum +95,000% Maximum Confidence Confidence P 10.00 0.90 0.73 1.06 8.99 0.67 1.46 0.23 0.07 BS 10.00 1.01 0.82 1.20 10.09 0.67 1.58 0.26 0.08 FS 10.00 1.56 1.38 1.73 15.56 1.11 2.00 0.25 0.08

P roductivity B reeding s ucces s F ledgling s ucces s

2,50

2,00

1,50

1,00

0,50

0,00 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

Years Fig. 3. Dynamics of the breeding parameters of the Eastern Imperial Eagle population in Bulgaria for the period 2000-2009

Breeding success Success rate Immature breeders %

1,80 s s

e 1,60 c c

u 1,40 s

g 1,20 n i

d 1,00 e e r

b 0,80

f o

0,60 e u l 0,40 a V 0,20 0,00 Years

Fig. 4. Dependence of the breeding success on the percentage of immature breeders

46 Increase of the Population of the Eastern Imperial Eagle (Aquila heliaca) in Bulgaria

Table 2. Comparison of productivity (PR), breeding success (BS), and fledglings success (FS) of pairs breeding in different regions: Sredna Gora/Eastern Rhodope (SG/ER), Dervent Heights/Western Strandzha (DH/WS), Southern Sakar (SS), Northern Sakar (NS), and the Tundja river valley (TV) (* statistically signifiant difference; ** statistically highly signifiant difference; *** statistically very highly signifiant difference). (One-way АNOVA analysis)

Productivity (PR) Region vs. region N recorded cases N recorded cases P SG/ER vs. DH/WS 22 24 0.001315** SG/ER vs. SS 22 63 0.871861 SG/ER vs. NS 22 21 0.021694* SG/ER vs. TV 22 18 0.542721 DH/WS vs. SS 24 63 0.001615** DH/WS vs. NS 24 21 0.322986 DH/WS vs. TV 24 18 0.000283*** SS vs. NS 63 21 0.027464* SS vs. TV 63 18 0.436376 NS vs. TV 21 18 0.005527** Breeding Success (BS) Region vs. region N recorded cases N recorded cases P SG/ER vs. DH/WS 17 24 0.013225* SG/ER vs. SS 17 56 0.925068 SG/ER vs. NS 17 21 0.111362 SG/ER vs. TV 17 14 0.410602 DH/WS vs. SS 24 56 0.008641** DH/WS vs. NS 24 21 0.362624 DH/WS vs. TV 24 14 0.001692** SS vs. NS 56 21 0.085169 SS vs. TV 56 14 0.451634 NS vs. TV 21 14 0.020528* Fledglings Success (FS) Region vs. region N recorded cases N recorded cases P SG/ER vs. DH/WS 11 22 0.032833* SG/ER vs. SS 11 29 0.06554 SG/ER vs. NS 11 17 0.105699 SG/ER vs. TV 11 9 0.420965 DH/WS vs. SS 22 29 0.746605 DH/WS vs. NS 22 17 0.611724 DH/WS vs. TV 22 9 0.004929** SS vs. NS 29 17 0.846432 SS vs. TV 29 9 0.010944* NS vs. TV 17 9 0.020143* success. No signifiant difference was recorded in indicator showed statistically highly signifiant dif� the s��uccess rate.rate. Statisti��c��ally � �v ery highly signi�f�� ferences (p<0.01) between mountain wooded areas cant differences in productivity were recorded be� and the area of Dervent Heights/Western Strandja. tween the pairs in the region of the Dervent Heights/ These differences were also valid for Dervent Western Strandja Mountains and those inhabiting Heights/Western Strandzha and Southern Sakar, as the Tundja river valley (p<0.001) (Table 2). This well as Northern Sakar �� an�d the T�u�n�dja ri�v��er �v��al�

47 Demerdzhiev D., G. Gradev, S. Stoychev, I. Ivanov, T. Petrov and S. Marin ley. Signifiant differences (p<0.05) were recorded ling success 1.59±0.38, but their success rate was the between pairs in the Sredna Gora/Eastern Rhodope lowest (48.69% ±22.76). Mountains and Northern Sakar, and between those For�� the�� ten�� years��’�� st��ud��y ��perio��d��, ��bree��d��ing ��imma�� breeding in Southern Sakar and Northern Sakar. ture eagles were not recorded in only 16.7% of the Regarding the breeding success ��(��Table ��2)�,�� sta� occupied territories. The presence of immature male tistically highly signifiant differences (p<0.01) birds (57%) in pairs was a bit higher than that of were recorded between Imperial Eagles breeding in immature females (43%). The presence of immature Dervent Heights/Western Strandzha and Southern birds in pairs was recorded after 2001 (Fig. 5). The Sakar, as well as between those in Dervent Heights/ maximum number of pairs consisting of an adult and Western Strandzha and the Tundzha river valley. an immature bird was recorded between 2003 and The ��d��ifferen�c��e�� in�� this�� in��d�i�c�ator�� between�� the�� mo��u�n� 2005, as in 2004 the number of pairs involving two tain wooded territories and Dervent Heights/Western adult individuals was almost equal to the number of Strandzha, and between Northern Sakar and the mixed pairs.�� Ele�v��en immat�u��re pairs o��ccu��pie�d� �d��iffer� Tundja river valley was signifiant. ent territories between 2002 and 2009. Eight of these Statistically highly signifiant differences in pairs were recorded in newly occupied and three in the fl fle e�dglings s��uccess (p(�p��<��0.01�) were re��c��or�d�e� be�� reoccupied territories. Since 2005, the number of tween Dervent Heights/Western Strandja and the adult pairs has been increasing. Tundja river valley, while those between Sredna Gora/Eastern Rhodope and Dervent Heights/Western Strandja and between the Tundja river valley and the Discussion two regions in the Sakar Mountains was signifiant Breeding distribution and habitat performance (p<0.05) (Table 2). The breeding parameters indicate highest val� The existing data on the breeding of the species in ues of the pairs breeding in Dervent Heights/Western the past, when it was widespread, is related to vari� Strandja, where during the period 2000-2009 with ous habitat types (Hr i s t o v ich 1890, Re i s e r 1984, n=24 occupied territories the mean value of the Le v e r k uhn 1907). This was followed by a period breeding success and productivity was 1.58±0.38, of dramatic decline between the 1950s and 1980s, the mean fledgling success 1.7±0.40 and the mean when�� bir�d��s of prey were �d�e�c��lare�d�� a pest an�d�� a �c��am� success rate 94.17% ±12.45. These are followed by paign for their extermination was launched (Pe t r o v the pairs breeding in Northern Sakar (n=21 cases of et al. 1996). This period is also related to a change occupied territories), as the mean productivity and in traditional farming, which resulted in serious frag� breeding success was 1.35±0.77, the mean fledgling mentation and loss of habitats, particularly evident in success 1.56±0.64 and the mean success rate 83.34% the plains.�� In�� the ��1960��s��, ��as�� a ��res�u��lt ��of�� h�u��man ��pres� ±20.4. The breeding success of the pairs (n=22) in sure, the species disappeared in most of its lowland the mountain-wooded areas of the Sredna Gora and localities, where it was easily accessible, and during Eastern Rhodope Mountains was not so good, as the next decade its nesting distribution was present the mean value for the study period was 0.97±0.97. mainly in mountains, where it had survived probably They had low fledgling success 1.17±0.94 and low due to the sparsely populated and not so accessible productivity 0.76±0.67. Their mean value of suc� regions (Mich e v , Pe t r o v 1979, 1985, Si m e o n o v et al. cess rate was 61.11% ±39.75. The lowest breeding 1990). Between 1970 and 1980, the Imperial Eagle success (0.65±0.44), fledgling success (0.88±0.64) was recorded in 21 localities, 76% of which were in and productivity (0.58±0.43) were recorded for pairs the mountains, including all certain ones (Mich e v , (n=18 cases) nesting in the Tundja river valley. Low Pe t r o v 1979, St o y ch e v et al. 2007, De m e r d z hi e v , values of mean breeding success (0.81±0.43) and m a nu s c r ipt ). During the next twenty years, 15 certain productivity (0.73±0.43) were observed with the breeding localities were known, 53%�� of�� which�� locat�� breeding group in the Southern Sakar Mountains, ed in the low hilly areas of the Sakar and the Western where 63 cases of occupied territories were record� Strandja Mountains (Da r a k chi e v , 1988, (Pe t r o v et ed. The birds nesting in this region had mean fledg� al. 1996, St o y ch e v 1997, St o y ch e v et al. 2004).

48 Increase of the Population of the Eastern Imperial Eagle (Aquila heliaca) in Bulgaria

Adult pair Mixed pair Immature pair

10 s r i 8 a P 6

0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 Years

Fig. 5. Age structure of the Eastern Imperial Eagle breeding population for the period 2000-2009

The recovery of the population started in the last decade of the 20th century was probably related Sakar and the Western Strandja Mountains, where to the existence ��of a stable Imperial Eagle pop�u��la� the species had survived in the sparsely populated tion in European Turkey (De m e r d z hi e v et al. 2011). border areas. The expansion of the population in SE The studies carried out in 2008 and 2009 in Turkish Bulgaria involves northward and westward coloni� Thrace as ��c�ertaine�� an ob��v��io�usly healthy an�� rela�� zation of new regions, holding many territories suit� tively abundant Eastern Imperial Eagle population, able for breeding. which gives us reason to presume that the pairs According to Ar a b a d z hi e v (1962) the Eastern breeding in SE Bulgaria represent the periphery of Imperial Eagle was found in the Sakar and the this Thracian population of Imperial Eagle expand� Strandja ��Mo�u��ntains ��till abo�u��t ��1940��, an�d�� then it �d��isap� ing north-westwards. peared��. This��,�� howe��v�er��,�� is�� at �v��arian�c��e with the infor� At the same time ��the ��d��egra�d��ation ��of�� the territo� mation from the local people, who know the species ries in the mountain-wooded habitat type that started quite well. According to them, there have been no pe� some twenty years ago continues after 2000. In the riods, when there were no Imperial Eagles (Pe t r o v , Eastern ��Rho��d��ope ��Mo��u��ntains, where only one bree��d� St o y ch e v 2002). The studies carried out in SE ing pair was recorded during the period 2000-2009 Bulgaria by different ornithologists during the 1970s (De m e r d z hi e v 2004), since 2004 this territory has and 1980s presumed the existence of 3-4 pairs in the been occupied by the male eagle only. A decrease in Sakar Mointains and 3-5 pairs in the Dervent Heights the number of Imperial Eagles inhabiting this moun� and the Western Strandja Mountains (Na n k in o v 1981, tain was recorded as early as the 1990s (Hr i s t o v , La m bu r o v 1985, Da r a k chi e v 1988). St o y n o v 2002). One of the two bree ��d�ing territo�� By 2000, six of all 8 occupied territories were ries in the Sredna Gora Mountains, which has been situated in the Sakar and the Western Strandja known since 1978 (Pe t r o v 1981), was not occupied Mountains.�� In�� the ��perio�d�� 200�1��-��200��9,�� 1��3�� newly ��oc�� by birds in�� 2009. ��The Imperial Eagles in this terri� cupied and 3 reoccupied territories were recorded. tory have not bred since�� 2004. ��A loss of a �‘��mo�u�n� Annually, zero to three new territories were o��ccu� tain type’ territory was also recorded in 1998 in the pied��, ��an ��a�v��erage ��of�� 1��.��7��8��±0.97�� du��ring ��the ��st��ud��y�� pe� Eastern Balkan Mountains (Ang e l o v 2009). In 2009 riod��, all�� of�� them�� sit��u�ate��d�� in�� lowlan��d�� an�d�� hilly are� only one pair nested in mountain habitat type. as at an altitude of 50 m to 280 m in SE Bulgaria. The species is often found in open plain areas The stabilization of the population in SE Bulgaria when�� the�� pop��u��lation ��is�� ab��u�n�d�ant�� an��d�� not�� perse��cu�t� in the 1990s and the subsequent increase during the ed (Ka t z n e r et al. 2003). The expanding Panonian

49 Demerdzhiev D., G. Gradev, S. Stoychev, I. Ivanov, T. Petrov and S. Marin

(Hungary, Slovakia) population of the Eastern the pairs had three chicks per pair, while in Bulgaria Imperial Eagle is also �c��hara�c��terize�d by re��-c��oloni� the pairs with two-chick broods were 40%, and those zation of lowland territories (Da n k o , Ch a v k o 1996, with three chicks only 6.9% (�De m e rd Dz hi H Ie v � m a Nnu U �- Ba g y u r a et al. 2002, Ho r v a th et al. 2011, Da n k o et s c r ipt ). Higher breeding success was recorded in the al. 2011). The Spanish Imperial Eagle (Aquila adal- population of the species in NW Kazakhstan – from berti Br e h m , 1861),�� whi�c��h, in an in�c��reasing pop�u��la� 1.3 to 2 for the period 1990-2002 (Br a gin , Ka t z n e r tion, occupies lowland territories, shows�� similar�� hab�� 2004) and for the Slovakian population for the period itat preferences (Go n z a l e z et al. 2008). As the living 2004-2007 (mean value 1.35) (Da n k o et al. 2011). conditions change, each habitat type can be crucial The lowest value of breeding parameters of for the preservation of the population. According to pairs nesting in the Tundja river valley was probably Go n z a l e z et al. (2008), all habitat types used by the due to the inexperience of the breeding birds occupy� Spanish Imperial ��Eagle,�� in�c�l��ud��ing ��also ��those ��harbor� ing new territories. In the period 2002-2009, 50% of ing few pairs, should be considered important for the the pairs that had occupied breeding territories, con� species conservation. sisted of partners in immature plumage. The region Breeding parameters is characterized by plains, considerable open areas and arable lands, and the nests of the Imperial Eagle Since the Imperial Eagle is a species with �‘��K��’ �d��emo� pairs are built on single trees or in isolated groups of graphic strategy, characterized by low reproductive trees, visible kilometers away, thus often subject to potential, balanced with signifiant life expectancy human disturbance. The low values of the breeding of breeding individuals, the survival of adults is the success and the productivity recorded for the pairs most important factor affecting the population growth breeding in the Southern Sakar Mountains were also (Ne wt o n 1979, Ka t z n e r et al. 2006, So utu l l o et al. due, to a certain extent, to human disturbance. Some 2008). With stable populations the annual mortality of the pairs breeding in the area are situated in the of adults is equal to renewability (Ric k l e f s 1973, immediate proximity of settlements or roads; being Ne wt o n 1979). often disturbed, they fail to raise chicks. However, The mean survival rate of breeders recorded some of the pairs nesting in this area occupied ter� for the period 2000-2009 was similar to that of the ritories of low quality with considerable overgrowth increasing population of the Spanish Imperial Eagle and not so good food resources (�De m e rd Dz hi H Ie v ��, m a Nn �- r t e g a (O et al. 2009). u s c r ipt ). Some of the birds breeding in this area have The annual mortality of breeders was lower than also been infertile for many years. The pairs breed� that of the declining local population of the Spanish ing in the Northern Sakar and the Western Strandja Imperial Eagle in Doñana (Fe r r e r 2001). High adult Mountains, occupying territories providing better mortality was recorded in the Eastern Imperial Eagle conditions and being less exposed to disturbance, population of the Naurzum Reserve (Kazakhstan) for had highest values of the breeding parameters. The the period 1999-2002, probably because this was a disappearing pairs in the mountain-wooded habitat migrating population (Rudnic k et al. 2005). The mean type, usually occupying territories of lower quality, values of the breeding parameters for the period 2000- also had lower values of the breeding parameters. 2009 indicated the good health of the population, The age of frst breeding is influenced by habitat which is a precondition for its growth. The population heterogeneity and population density (Kr ug e r 2005). of Imperial Eagles in Hungary had better breeding suc� In the raptor breeding populations, variable percent� cess and fledgling success for the period 2001-2009, age is generally made up of individuals in non-adult respectively the mean values of 1.15 and 1.72, which plumage (Ne wt o n 1979). Breeding of non-adults was probably due to the higher percentage of three- within the population is determined by two main fac� chick broods (Ho r v a th et al. 2011). The mean success tors: 1. Increased adult mortality enables younger rate for the period 2001-2009 in the Hungarian popu� birds to breed replacing dead adults (Ba l b o ntin et al. lation was 67%, as for the Bulgarian population it was 2003, Fe r r e r 2001, Fe r r e r et al. 2003); 2. Increased similar 64%. For the same period, however, 48% of resource availability encourages non-adult breeders the pairs in Hungary had two chicks each, and 14% of (Wy l l i e , Ne wt o n 1991, Br o m m e r et al. 1998).

50 Increase of the Population of the Eastern Imperial Eagle (Aquila heliaca) in Bulgaria

High�� a��du��lt ��mortality an�d�� a�v��ailability of forag� territory ��in the Western Stran�d��ja Mo�u��ntains was re� ing and nesting sites can account for the presence corded during the study period. One of them was an of�� non��-��a��du��lt ��bir�d��s�� in ��pairs.�� In�� the ��f��rst� �c��ase,�� a sig� adult found dead under the nest, and the other poi� nifiant part of the pairs were “mixed”, consisting soned bird was a fledgling found in the nest. One of an adult and an immature bird replacing a dead year later the breeding territory was occupied by a mate (Fe r r e r 2001, Fe r r e r et al. 2003). On the new immature pair. One case of direct persecution other hand, increased resource availability and va� was reported also in the Strandja Mountains when a cant territories could encourage non-adults to breed local shepherd killed an eagle near the nest and then (Wy l l i e , Ne wt o n 1991, Br o o m e r et al. 1998). In cut the bird’s legs (one of the legs was provided to these cases, pairs consisting of two immature birds the National Museum of Natural History). The bird colonize new territories. The peak of ‘mixed pairs’ in was probably poisoned, because it could not take off 2004 was defnitely related to the higher mortality of from the ground. An immature Imperial Eagle shot breeders recorded for that year (9.7%).�� The ��appear�� with 12 pellets was recorded during the study period. ance of immature pairs after 2002 was related to the There was one recorded case of nest robbing in the colonization of new territories, indicating population Tundja river valley, when local youths took the eggs growth. With the increase of the Spanish Imperial at Easter time. Eagle population, non-adult pairs occupy new ter� Electrocution or collisions represent potential ritories (Go n z a l e z et al. 2006, Or t e g a et al. 2009). threats. One of the juvenile Imperial Eagles tagged with satellite transmitters was found electrocuted Threats and conservation at a distance of 1.5 km from its nest. The power The loss of breeding and feeding habitats is one of line network in Bulgaria includes many dangerous the main threats. Illegal felling of high trees deprives structures posing risks to birds (St o y ch e v , Ka r a f e i z o v the Imperial Eagle of suitable nesting substrate. Most 2004). The study on the risky ��20 kV�� power lines c�ar�� of the nests are built on Poplar trees (Populus sp. L.), ried out in 2004 within four Important Bird Areas often near roads, where the trees are easily accessible. (IBAs)�� of�� signi�fi��an�c��e for the bree�d��ing of the spe� With the increase of the population, the colonization cies, or in temporary settlement areas, revealed high of new regions can be hindered if high single trees in mortality rates of raptors caused by electrocution suitable breeding territories are cut. Planned clearing (De m e r d z hi e v et al. 2009). of big forest areas also has a negative effect on the po� Construction of wind farms and solar parks tential nesting substrate of the species.�� Habitat frag� is another potential threat to Imperial Eagles. The mentation is perhaps the most serious factor, which green ��energy�� be��c��oming ��in��c��reasingly ��pop��u��lar in re� could negatively affect the population in the future. cent years, involving the construction of large-scale Tilling ��v��ast ��areas ��aban�d��one�d�� for many years or tra�d�i� wind farms or solar facilities result in devastation of tionally used as pastures in the Sakar and the Sredna eagles’ habitats and key prey species; these innova� Gora�� Mo�u��ntains ��an�d�� t�u��rning ��them ��into ��v��ineyar�d��s,�� or� tions could also be a direct cause of bird mortality. chards, or arable lands result in decreased numbers of There are investment plans for the construction of prey species. Disturbance during the breeding season wind farms or solar parks within the territories of ten is another important threat. In the Tundja river valley, Imperial Eagle pairs breeding in Bulgaria. the Sakar and the Western Strandja Mountains, the Natural disasters represent another important nests are situated in open plains and sometimes close reason for bird mortality during the fledging period. to agricultural felds and roads. Eagles are used to the Nine cases of chicks falling off the nests in storms presence of local shepherds and let them come close, were recorded during the period 2000-2009; these often even under the nest tree, while incubating (own incidents ��c�a�u��se�d�� the �d��eath of fo�u��r eaglets an�d�� per� data). Farming activities involving more people and/ manent injury of one. or agricultural machinery result in high disturbance Conservation activities implemented by both and brood loss. organizations – BSPB and Green Balkans, included: One� �c��ertain � �case of phosphoroorgani�� pesti�� guarding of endangered nest sites; awareness raising cide poisoning of Imperial Eagles from a breeding campaigns; replacement of nests built at endangered

51 Demerdzhiev D., G. Gradev, S. Stoychev, I. Ivanov, T. Petrov and S. Marin sites; construction of artifiial nests; rehabilitation of The eagles breeding in the Western Strandzha injured nestlings fallen from the nests; restriction of Mountains had higher breeding success, hence high� forestry operation and agriculture feld work; supple� er productivity, than the pairs in the other regions. mentary feeding; ringing of nestlings; satellite and The presence of immature pairs in the popula� radio tracking; educational activities; purchase of tion is related to newly occupied or reoccupied ter� land around Imperial Eagle nests; planting of Poplar ritories. trees in good nesting habitats; and prevention of Imperial ��Eagle�� habitats ��in ��B�u��lgaria ��are ��ins�u�f� damage caused by European Sousliks (Spermophilus fiiently protected. citellus Linn a e u s , 1766). All these systematic conservation activities have undoubtedly contributed to the population sta� Acknowledgements: We would like to thank the following bilization and the subsequent increase.�� Habitat �c��on� institutions and organizations for their fnancial support of the servation is of key signifiance for the stability and Eastern Imperial Eagle research and conservation activities: the the continuous increase of the population. Currently, Bulgarian Ministry of Environment and Waters, Whitley Laing Foundation, People’s Tru�st for End�angere��d� Spec�ies, EURO� none of the active Imperial Eagle nests is situated NATUR, Vogelpark Walsrode Fonds GmbH, CBD-Habitat. within a protected area, as only an insignifiant part Out thanks also go to Ivaylo Angelov, Nikolai Terziev, of the hunting territories of two Imperial eagle pairs Georgi Popgeorgiev, Prof. Zlatozar Boev, Vladimir Trifonov, Nedko�� Ne��d�yalko��v��,�� Atanas�� Demer��d��zhie�v��, Georgi�� Georgie��v��, Dim�� is protected. More territories inhabited by Imperial itar Plachiyski, Georgi Gerdzhikov, Dobromir Dobrev, Vladimir Eagles should be protected to secure the stability of Dobrev, Kiril Metodiev, Vanyo Angelov, Silviya Dyulgerova, the population. Girgina Daskalova, Petar Yankov, Borislav Tonchev, Marin Kurtev, Borislav Borisov, Hristo Hristov, Hristo Nikolov, Ivaylo Klisurov, Konstantin Dichev, Dimitar Popov, Iliyan Stoev, Do� bromir Dobrinov, Dimitar Marinov, Konstantin Popov, Hristina Conclusions Klisurova, Victor Garcia Matarranz, Lyubomir Andreev for providing valuable information and support. The Eastern Imperial Eagle population in the coun� Special thanks go to Mr. Dave Doyle for his kind assis� try is increasing by an average of 1.78 pairs per year, tance and efforts invested in editing the English version of this the newly colonized territories being lowlands in SE paper. Without listing their names we would like to express our Bulgaria, while the number of mountain-wooded gratitude to all volunteers who spent many days in the feld, pairs is decreasing. guarding or searching for nests.

References

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Увеличаване на популацията на източния царски орел (Aquila heliaca) в България

Д. Демерджиев, Г. Градев, С. Стойчев, И. Иванов, Ц. Петров, С. Марин

(Резюме) След 2000 г., системните консервационни дейности довеждат до подобряване на популацията на Източния Царски орел (Aquila heliaca Sa v ign y 1809) в България. Популацията се изчислява на 25-30 двойки. През периода 2001-2009 г. са регистрирани 13 ново заети и 3 повторно заети територии. През 2009 г. броят на известните заети територии нараства до 20. Ежегодно са отчитани заетите територии, гнездящите двой� ки, гнездовите параметри на популацията, преживяемостта при възрастните индивиди и възрастовата структура на гнездовата популация. Средните стойности на гнездовите параметри на популацията за периода 2000-2009 г. са както следва: продуктивност 0.90±0.23; гнездови успех 1.01±0.26; размножите� лен успех 1.56±0.25; и успеваемост 64.45% ±11.52. За опазването на вида се изпълняват дейности като охрана на гнезда, рехабилитация на ранени птици и последващо връщане в природата, “преместване на двойки”, изкуствено подхранване, изграждане на изкуствени гнезда, повишаване на осведомеността сред местната общност и власти, управление на гнездови местообитания, опръстеняване на малки в гнезда, сателитно и радио проследяване и закупуване на земи около гнездата. Основните заплахи за вида са загуба на местообитания, безпокойство, отстрел, отравяне и природни бедствия.