j. RaptorRes. 34(4):293-298 ¸ 2000 The Raptor Research Foundation, Inc.

NEST FEATURES AND NEST-TREE CHARACTERISTICS OF SHORT-TOED EAGLES (CIRCAETUS GALLICUS) IN THE DADIA-LEFKIMI-SOUFLI FOREST, NORTHEASTERN GREECE

DIMITRIS E. BAKALOUDIS 1 Schoolof Animal and MicrobialSciences, Unive•xity of Reading,Whiteknights, P.O. Box228, Reading,RG6 6AJ, U K

CHP. ISTOS G. VLACHOS Departmentof Forestryand Natural Environment,Aristotle University of Thessalonihi,P.O. Box 241, Thessalonihi54006, Greece

GRAHAMJ. HOLLOWAY Schoolof Animal and MicrobialSciences, University of Reading,Whiteknights, P O. Box228, Reading,RG6 6AJ, U K

AI3STP•ACT.-•Dataon nest features and nest-tree characteristicsof 29 nest trees of Short-toed Eagles ( Circaetusgallicus) were comparedwith the samenumber of paired, randomly-selectedtrees in the Dadia- Lefkimi-Soufliforest complex,northeastern Greece. Short-toedEagles usually nested in Calabrianpine (Pinusbrutia, 83%) treesthat were either dominant(87%) or intermediate(13%) in the canopy.Most nestswere in the largesttrees in termsof height (i = 13.8 _+0.4 m, _+SE)and diameterat breastheight (i = 49.7 + 1.6 cm) in stands.Nests were located in the loweror middlethird of the canopyat a mean height of 8.6 + 0.41 m and on horizontal branches at a mean distance of 133 cm _+ 12.4 cm from trunks. A tendencyfor building nestson the south-facingside of canopiesof nest trees was detected (mean angle = 178ø, angular deviations = 58ø). Short-toedEagles selected nest trees that provided them with easyaccess while also providing protection from predators and inclement weather. KEYWORDS: Short-toedEagle, Circaetus gallicus; nest features; nest-tree characteristics; Greece.

Caracteristicasdel nido y de los firbolescon nido de Circaetusgallicus en el bosqueDadia-Lefkimi-Soufli en el noreste de Grecia

REst3MEN.--Comparamoslos datossobre las caracteristicasde 29 nidos de Circaetusgallicus con el mismo nfimero de firbolesseleccionados al azar en el complejo de bosquesde Dadia-Lefkimi-Souflien el norestede Grecia. Circaetusgallicus anida usualmenteen firbolesde Pinus brutia83% los cualesfueron dominantes(87%) o intermedio (13%) en el dosel. La mayoriade los nidos se encontraronen los firboles mas grandes en t6rminos de altura (i = 13.8 + 0.4 m, +_SE) en los rodales. Los nidos fueron localizadosen la parte baja y el tercio medio del dosel a una altura media de 8.6 + 0.41 men ramas horizontales a una distancia media de 133 _ 12.4 cm del tronco. Se detect6 la tendencia de construir los nidosen el costadosur del dosel (mean angle = 178ø, angular deviations = 58ø). Circaetusgallicus seleccion6firboles que le proporcionaronun accesofftcil, como tambi6n protecci6nde losdepredadores y del inclemente clima. [Traducci6n de C6sar Marquez]

The Short-toedEagle ( Circaetusgallicus) is a tree- evergreen oak and mixed deciduouswoodland in nesting accipitrid (Cramp and Simmons 1980), central Italy (Petretti 1988), mixed conifer-decid- nesting in a variety of forest types, such as open uous forests in north-western Italy (Bocca 1989), coniferousforests in France (Thiollay 1968), dense and dry pine forestswith mosses(Sphagmum spp.) in the ground layer in Belarus (Ivanovsky1992). Despite considerable interest in the ecology of • Present address:Aristotle Universityof Thessaloniki, Department of Forestry and Natural Environment, Lab- Short-toed Eaglesin Mediterranean countries,few oratory of Wildlife and Freshwater Fisheries, P.O. Box studies have been conducted to describe the struc- 241, Thessaloniki 54006, Greece. ture of nest trees favored by the species(Petretti

293 294 BAKALOUDISET AL. VOL. 34, NO. 4

1988, Vlachos and Papageorgiou1994). No previ- ritories including occupied and old nests.Data on nest- ous studieshave been attempted to describe and tree characteristicswere collected during August and Septemberof 1996-97 after fledging.We recorded the compare actual nest trees with availabletrees. following information to describe each nest tree: tree A detailed analysisof Short-toedEagle nest trees species,crown class (dominant, intermediate, or sup- in the Dadia-Lefkimi-Soufli forest complex was car- pressed), trunk shape (straight, slightlycrooked, crook- ried out to determine the most important char- ed, forked, pitchforked, or without top), and canopy shape (condensed,dense, slack,or light). The condition acteristicsdetermining the choice of nest trees. of nest trees was describedas good, medium (evidence The aims of this studywere to describenest struc- of fire on bark), or bad (both evidenceof fire and epi- ture and to evaluate nest-tree characteristics of phytic growth). Nest-tree brancheswere measured and Short-toed Eaglesby comparing actual nest trees classifiedaccording to their density(I-->20 brancheson the trunk, 11--10-20 branches on the trunk, or III-•<10 with randomly-selectedtrees. branches on the trunk) and their size as (thick-•>50% of branches with a diameter >12 cm, medium-->50% STUDY AREA of branches with a diameter 8-12 cm, or thin-->50% of The studywas conducted in the Dadia-Lefkimi-Soufli branches with a diameter <8 cm). Diameter at breast (D-L-S) forest complex, in the central part of EvrosPre- height (dbh) wasmeasured using a dbh tape and the age fecture, northeastern Greece (40ø59'-41ø15'N, 26019'- was determined using an increment core by counting 26ø36'E). The region is on the eastern edge of the Ro- growth rings. Height of nest trees, height of nestsabove dopi mountainchain in westernThrace. Elevations range ground, and height to living canopywere measuredwith from 20-700 m and steep-sidedvalleys crisscross the area. a Blumme-Leissaltimeter (accuracy+0.25 m). Canopy The climate is submediterranean and mean monthly height of nest trees was estimated by subtracting the temperaturesin the area range from 25øCin July to 4øC height of the bottom of the canopyto the ground from in January.Mean annual precipitationis 664 mm. North- the height of the tree. Each nestwas assigned to the low- erly winds predominate during the year following the er, middle, or upper third of the canopy. north-south orientation of the Evrosvalley. In order to compare nest-treecharacteristics within the The structureand compositionof the vegetationin the same forest stand, the same number (29) of nonnest D-L-S forest complex are the result of a combinationof trees were randomly selected from neighboring areas. climate, soils,and intensivepast human influence (Dafis Each random tree was situated from 70-400 m from nest 1973). The studyarea is coveredby a mosaicof different trees. Three stepswere followed to establisheach ran- habitat types, such as agricultural lands, grasslands, dom tree. First, the area centered on the nest tree was shrublands,rocky areas,pine forests,oak forests,degra- divided into four quadrants (1 = northeast, 2 = south- dated oak forests,and mixed pine-oak forests.The main east, 3 = southwest,and 4 = northwest) and one of these overstorytree speciesare pines,including Calabrian pine was randomly selected.Secondly, two randomly-selected (P•nusbrutia) and black pine (P. nigra). The understory numbers between 0-400 were selected to calculate the is mixed with pines, oaks (Quercusconferta, Q. pubescens,distance of the random point along the north-southaxis Q. sessiliflora,and Q. cerris),and various shrub species and the east-westaxis. The intersectionof lines extending ( Phyllireamedia, Arbutus andrachne, Erica arborea,Juniperus from these points identified the location of the center of oxycedrus,Carpinus orientalis, Ost•ya carpinifolia, and Fraxi- the random tree. Finally,the closestdominant tree to this nusornus). Approximately 19.5% (7250 ha) of the 37 156 centered point that wassimilar in dbh with the nest tree ha studyarea consistsof two core areasthat were estab- was selected and defined as the random nest tree (Titus lished as protected areasfor birds of prey in 1980. and Mosher 1981). When random points identified The studyarea supportsa remarkablediversity of wild- points in nonforested areas such as grasslands,shrub- life includingBlack Vultures (Aegypiusmonachus), Griffon lands, and/or cultivated areas, or in an area with only Vultures (Gypsfulvus), LesserSpotted Eagles (Aquila po- young trees,they were rejectedand the aboveprocedure marina), Imperial Eagles(Aquila heliaca),Booted Eagles was reinitiated. The same measurements were made on ( H•eraaetuspennatus), wolves ( Canislupus), jackals ( Canis the randomly-selectedtrees as nest trees,apart from var- aureus),wild cats (Felissylvestris), brown hares (Lepuseu- iables concerning nest characteristics. ropaeus),wild boars (Sus scrofa),large whip snakes(Col- Nest features were describedquantitatively in terms of uberjuffularis), grasssnakes (Natrix natfix), dice snakes the distance to the trunk of the tree in cm, the diameter (Natrix tesselata),nose-horned vipers ( Viperaammodytes), of branchessupporting nests against trunks in cm, max- and green lizards (Lacerta viridis) (Bakaloudis et al. imum and minimum diameter axis of nestsin cm, depth 1998). of nest cups in cm, and the height of the nest in cm. Nest orientation was determined as the mean flying di- METHODS rection to and from the nest, and nest orientation in re- As many occupiedShort-toed Eagle territories as pos- lation to trunk was determined as the angle between a siblewere locatedin the studyarea during the 1996-97 line joining the nestwith the trunk and magneticnorth. field seasonsusing (a) historicaldescriptions of tradition- Nest orientation and nest orientation in relation to the al nestingsites, (b) territorial behaviorsof breedingpairs tree trunk were measuredwith a compass,recording the noted from high vantage points, and (c) extensiveex- angle in degreesfrom magnetic north. ploratorysurveys on foot (Fuller and Mosher 1987). A All variableswere tested for heterogeneityof variances total of 29 nestswere located in 22 Short-toedEagle ter- using Bartlett's test (Zar 1996) and for normality using DECEMBER 2000 NESTS OF SHORT-TOED EAGLES IN G•ECE 295

Table 1. Characteristicsof 29 Short-toed Eagle nests in the Dadia-Lefkimi-Soufiiforest complex, northeastern Greece.

VARIABLE MEAN -----SE RANGE CV

Height of nest above ground (m) 8.67 m 0.41 5.5-12.25 20.47 Diameter of branch supporting the nest (cm) 12.46 m 0.91 7.5-26 31.71 Distance from trunk (cm) 133.6 m 12.4 45-231 38.72 Diameter of nest (cm) max. 61.75 m 1.42 8-74 10.26 Diameter of nest (cm) min. 48.44 + 1.06 40-59 9.52 Depth of nest-cup (cm) 7.17 -+ 0.43 5-13 26.63 Height of nest (cm) 17.13 --- 0.93 12-26 23.74 Orientation of nest in relation to trunk (ø) 178 Orientation of nest (ø) 171

Anderson-Darling test. Variables that did not meet the angle = 171ø, s = 53ø, r = 0.57) and the distribu- assumptionsof homoscedasticityand normality were log- tion of orientation deviatedsignificantly from ran- transformed prior to parametric analysis.Normally-dis- tributed variables were analyzed using paired-sample t- dom (Rayleigh'stest: z = 9.34, P < 0.001; Fig. lb). tests,but those not meeting normality assumptionsafter Nestsgenerally were constructedusing dead pine transformationwere analyzed using the nonparametric twigs,with or without needles,and oak twigsmea- equivalent Wilcoxon matched-pair test. Nominal vari- suring 5-15 cm long and 1-3 cm in diameter. Nest ableswere compared using chi-squareanalysis. We used Kolmogorov-Smirnovtests to test for uniformity in nest cupswere lined with green pine needlesand green location in nest trees.Variables expressed as percentages oak leaves.Materials were added to nestsby adult were arcsine transformed to standardize variance. Circu- eaglesduring the breeding seasonuntil young ea- lar variableswere analyzedusing Rayleigh'sz test for cir- gles fledged from nests.Nests measured on aver- cular uniformity (Batschelet 1981, Zar 1996). All statisti- age 61.7 + 1.4 X 48.4 --- 1.1 cm (N = 29). Short- cal analyseswere performed using the Minitab statistical software (version 12) and differences were considered toed Eaglestend to build new nestseach breeding significantwith ct = 0.05. season.In a sample of 35 nesting attempts in the study area during 1996-97, seven pairs repaired RESULTS and reusedthe samenest for two consecutiveyears Three types of Short-toed Eagle nestswere re- and three pairs used the same nest for more than corded in the studyarea accordingto their position two years (unpubl. data). within the canopy of nest trees. Type I nestswere Short-toedEagles nested exclusively in Calabrian located in the lower third of the canopyon large, (83%) and black (17%) pines.All nest treeswere horizontal forked branchesand awayfrom trunks. alive and fell into the largest diameter size classes. Type II nestswere similar, but were located in the The structure of nest trees was similar to random middle third of the canopy,and Type III nestswere nest trees (Table 2). We could not detect a differ- locatedon the top of relatively-flatcanopies near to ence between nest tree and randomly-selected trunks and open from above.Nests were not distrib- trees in terms of their dbh, height, canopyheight, uted uniformly acrossthe three nest types(Kolmo- or age. Nest treeswere either dominant (87%) or gorov-Smirnovtest; Dm= = 7, P < 0.05) and were intermediate(13%) in the canopy;random trees more often located in the lower or middle third were all dominant (2 x 2 contingencytest, X2 = than the upper third of the canopy. 2.071, df = 1, P = 0.150). Nest trees had either Short-toedEagles had a tendencyto build nests slightlycrooked (90%) or straight (10%) trunks, on the south-facingsides of the canopy (mean an- which was not significantlydifferent from random gle = 178ø, angular deviations = 58ø, measureof trees (93% slightlycrooked, 7% straight) (2 X 2 concentration r = 0.49; Table 1), which was signif- contingencytest, X2 = 0.25, df = 1, P = 0.61). Ad- icantly different from a uniform distribution (Ray- ditionally, there were no differences between nest leigh's test: z = 6.84, P < 0.001; Fig. la). The po- trees and randomly-selectedtrees in canopyshape sition of each nest offered incoming eagles a (2 X 3 contingencytest, X2 = 3.39, df = 2, P = particular direction of approach to the nest. The 0.18) or the condition of the trunk (2 X 3 contin- mean orientation of nests was also south (mean gency test, X2 = 0.9, df = 2, P = 0.63). However, 296 BAKALOUr•S ET AL. VOL. 34, NO. 4

N (a) Table 2. Characteristics of 29 Short-toed Eagle nest trees and 29 randomly-selectedmature trees in the Dad- ia-Lefkimi-Soufli forest complex, northeastern Greece (i NW-- i •,.NE + SE). P-value indicates statisticalsignificance of differ- 178 ø ence between the pairs of means. $ = 58 ø r= 0.49 VARIABLES NEST TREE RANDOM TREE P-VALUE w E dbh (cm) 49.7 + 1.6 47.9 + 0.6 0.66a Height (m) 13.8 +_0.4 14.2 + 0.4 0.38 Canopy height (m) 5.8 -+ 0.3 6.0 +_0.2 0.38 Age (years) 87.5 +- 3.1 85.3 --- 3.0 0.51 SW'•• •'SE Value based on paired sampleWilcoxon test. S

in our study area. Calabrian pine trees generally have only a few, thick branches and an oval-shaped canopy.Black pines have many more and thinner branches with a relativelyflat canopy.These differ- ences may explain the Short-toed Eagle's prefer- ence for Calabrian pines for nesting. In the same studyarea, similar findingswere alsodemonstrated by Vlachos and Papageorgiou (1994) who found (b) N that 80% and 20% of nests were built on Calabrian 12

10 and black pines, respectively.In Belarus, Short- toed Eagles nest exclusivelyin pines (Ivanovsky 1992). In northwestern Italy, they nest in Larix de- cidua and Pinus silvestris(Bocca 1989) and in cen- s = 53 ø tral Italy they nest in evergreen oak and deciduous • r=171o 0.57 trees (Petretti 1988). NW NI All nest trees were dominant with mean height and mean height of canopy of 13.8 and 5.8 m, re- spectively.Nest trees were also mature ranging from 72-135-yr old and they belongedto the high- W;SW• •Ax SE '.Eest diameter size classes with a mean dbh of 49.7 cm. Short-toed Eagles showed a preference for S building their nests in trees containing thicker branches and >10 branches per trunk. Trees with F•gure 1. (a) Orientation of Short-toed Eagle nestsin relation to nest-tree trunk and (b) orientations of flight this structure probably provide greater shelter path of Short-toedEagles to and from nestsin the Dadia- from predators and inclement weather while, at Lefkimi-Soufli forest complex (N = 29). the same time, provide support for nests (Solonen 1982). Such trees are the result of a lack of com- petition during early successionalstages (Dafis the majority of nest trees had many (42%) and 1990) or from varying intensifies of competition some (55%) branches,as opposed to random trees experienced over time (Begon et al. 1996). which had only some (65%) and few (28%) Short-toed Eaglespreferred to build their nests branches(2 X 3 contingencytest, X2 = 12.84, df on the south-facingside of the canopyof nest trees. = 2, P = 0.002). Branches were also thicker in nest We suggestseveral reasons they do this. First, the trees than in random trees (2 X 3 contingencytest, strong relationship between nest position in rela- X•= 9.68, df = 2, P = 0.008). tion to trunk and slope orientation offers a partic- DISCUSSION ular direction for adults to access nests (Newton Short-toed Eagleswere found to use mostlyCal- 1979, Siegand Becker1990) and providesa favor- abrian (83%) and black (17%) pines for nesting able setting for fledglingswhen they first fly from DECEMBER2000 NESTS OF SHORT-TOED EAGLES IN GREECE 297 nests. Petretti (1988) also noted that 42.8% of clement weather (Colias and Colias 1984). In the Short-toedEagle nestsin Italy were situatedon lat- Dofiana National Park, Spain,where westerlywinds eral branchesoverlooking steep slopes.Secondly, prevail, Black Kites (Milvus migrans)build their a preferred orientationfor nestshas also been ob- nests on the leeward sides of tree crowns maximiz- served in several raptors and may be related to ing the sheltering effect of trees (Vinuela and Sun- breeding performance (Vinuela and Sunyer1992) yer 1992). At Sagehen Creek in California, where by providinga favorableenvironment both for the inclement weather is mainly from the south,Amer- incubating female and nestlings.The main mete- ican Kestrels (Falcosparverius) situate their neststo orological factors that might influence nest orien- avoid this cold direction (Balgooyen1976, 1990, tation and reproductive successare temperature Raphael 1985). Similarly, Olsen and Olsen (1989) early in the breeding season,direct solarradiation in Canberra, Australia, noted that only 10.3% of during hotter days,and avoidanceof other inclem- Peregrine Falcon (Falco peregrinus)nests faced ent conditions.In D-L-Sforest complex, Short-toed southwestwhere most inclement weather originat- Eaglesprobably gain warmth in the beginning of ed. breeding seasonwhen temperaturesare still low by In our study,nest features of Short-toed Eagles situatingnests to the south sidesof nest trees. Sim- agreed with those reported in previous studies. ilarly, Ivanovsky(1992) in Belarus,found that nests Newton (1979), Petretti (1988), and Vlachos and were directed towards the south or southeast when Papageorgiou (1994) noted the tendency for they were situated below the top of trees. Mosher Short-toed Eagles to build small nests for their and White (1976) in Alaska and Poole and Brom- body size, and to build a new nest in a different ley (1988) in the centralCanadian Arctic noted the place each year. Petretti (1988) reported a total of tendency for Golden Eagles (Aquila chrysaetos)to 39 nestingattempts, but the samenest wasused in place their nestsin a southeasterlydirection and two consecutiveyears twice and for three consec- Buchanan et al. (1993) have recorded a mean utive years only once. Ivanovsky (1992) reported southeasterlydirection for Spotted Owl (Strix occi- that each pair had 1-9 alternate nests,and the dis- dentalis) nests in the Cascade Mountains in Wash- tance between them varied from 300-1500 m. Ea- ington for Spotted Owl nests.Additionally, Tjern- gles in our study differed in that they tended to berg (1983) in Sweden, has mentioned the maintain the samenests for longer periods of time, preferenceof Golden Eaglesto breed on cliffsfac- or to use another nest in close proximity to the ing south or southwest. first. This may have been due to nest site compe- Eighty-sixpercent of the nestswere locatedwith- tition with other raptors.The D-L-Sforest complex in the foliage of nest trees on large horizontal supportsa diverseconcentration of raptors which branches at a mean distance of 133 cm from possibly creates strong interspecific competition trunks. Shadowed by a roof of branches from for nesting sites (Vlachos 1989). Another expla- above,these nestsprobably provide both conceal- nation is that Short-toedEagles are possiblyat car- ment from other avianpredators (Newton 1979) rying capacityin the D-L-S forest complex (Hall- and direct insulation from the sun. Short-toed Ea- man 1979) and so remain, year after year,at the glesbuild their nestsin foliage to protect incubat- same nest sites because no other sites are available. ing females, eggs, and nestlingsfrom aerial avian We observed Short-toed Eagles frequently car- predators (e.g., Eagle Owls [Bubobubo], Common rying green twigsto their nests,a behavior that has Ravens [ Corvus corax], and Hooded Carrion Crows alsobeen noted by Petretti (1988). Newton (1979) [Corvus coronecornix] ), which were common in the reported this habit for other raptors,and many ex- studyarea. In addition, branchesabove nests pro- planationsincluding nest sanitation and the main- vide cover from direct solar radiation minimizing tenance of optimum humidity have been suggested thermal stressin newly-hatchednestlings, especial- for this behavior.The most widely acceptedexpla- ly during the hottestdays when, in somecases, the nation is that raptors bring green vegetation to temperaturerises to 40-43øC. their nests to advertiseterritory occupancy (New- In our study area, the predominant winds are ton 1979). A further explanationis that the contin- northerly and the majority of the storms arrive ual addition of nesting material increasesthe size from the north (Flokas 1990). Overall, the place- of the nest to accommodatethe increasingsize and ment of nestsby birds oppositeto prevailingwinds activityof the nestlings,particularly when they be- and storms may be critical to avoid the most in- gin to exercisetheir wings(Newton 1979). Perhaps 298 BAKALOUDIS ET AL. VOL. 34, NO. 4 this is more important for Short-toed Eagles be- Millsap, K.W. Cline and D.M. Bird [EDS.], Raptor causethey build very small nestsin comparisonto management techiquesmanualß Natl. Wildl. Fed., Sci. their size. Tech. Ser. No. 10. Washington, DC U.S.Aß HALLMAN, B.C.G. 1979. Guidelines for the conservation ACKNOWLEDGMENTS of birds of prey in Evros. IUCN/WWF Rep. 1684, We are grateful to K. Bakaloudis, S. Alatzias, P. Gou- IUCN/WWF, London, U.K. d•akas, M. Tsakaldimi, and K. Poirazidis for field assis- IVANOVSKY,V.V. 1992. Short-toed Eagle in Belarus:cur- tance, and to the Ministry of Agriculture, General Sec- rent statusand ecology.Pages 69-77 in E.N. Kuro- retariat of Forests and Natural Environment, for chkin [ED.], Modern ornithology 1991. Nauka Pub- permissionto carry out this study.G.R. Bortolotti and an lishers, Moscow, Russia. anonymousreviewer kindly made many valuable recom- MOSHER,J.A. AND C.M. WHITE. 1976. 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