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Density, Nest Sites, Diet, and Productivity of Common Buzzards (Buteo Buteo) in the Italian Pre-Alps

Density, Nest Sites, Diet, and Productivity of Common Buzzards (Buteo Buteo) in the Italian Pre-Alps

j RaptorRes. 36(1):24-32 ¸ 2002 The Raptor ResearchFoundation, Inc.

DENSITY, NEST SITES, DIET, AND PRODUCTIVITY OF COMMON ( BUTEO) IN THE ITALIAN PRE-

FABRIZIO SERGIO 1 Edward GreyInstitute of Field Ornitholo•, Departmentof Zoolog,South Paths Road, OxfordOX1 3PS, U.K

ALBERTO BOTO, CHIARA SCANDOLAIL{, AND GIUSEPPE BOGLIANI Dipartimentodi BiologiaAnitaale, Piazza Botta 9, 27100 Pavia,

ABSTRACT.--Westudied a Common (Buteobuteo) population of 32-35 territorial pairs between 1993 and 1999 in a 113-km9 plot locatedin the central Italian pre-Alps.Density progressively increased from 28 to 31 pairs/100 km2. Territorial pairs were regularlydispersed with a mean distancef?om the nearest occupied nest of 1108 m (N = 108). Eighty-onepercent of 108 used nest siteswere on cliffs, while the remaining 19% were placedon mature trees.Each year, 16-21% of the nestsbuilt by Common Buzzardswere taken over by migratory Black Kites ( m}grans).Mean laying date was 9 April (earliest = 7 March, latest 30 April, N = 45). Mean clutch sizewas 2.32 (N = 19). Hatching successwas 91% (N: 33 eggst?om 14 clutches).Mean brood size at hatching was 2.14 (N = 14). Eighty-nine percentof the territorialpairs laid (N = 37) and 72% raisedat leastone chickto fledging(N = 100). Mean number of fledgedyoung was 1.07 per territorialpair (N: 100), 1.11 per reproductive pair (N: 33), and 1.49per successfulpair (N = 72), with no significantdifferences among years. Diet was dominated by medium to s•nall passetines,small ,and .Recorded densityand productivitywere comparableand often higher than those reported for other European populations. Human persecutionwas high until the 1970s,but is currentlyunimportant. Future conversion of young coppice standsto mature tbrest could further favor pre-Alpine populations of Common Buzzards. I•¾ WOP.DS: breedingsuccess; Buteo buteo; CommonBuzzard; density; diet; forestry; Italy; pre-Alps.

Densidad, sitiosnido, dieta y productividadde los gavilanescomunes (Buteo lmteo) en los Pre Alpes Italianos R•suM•N.--Estudiamosuna poblaci6nde gavilanescomunes (Buteo tmteo) de 32-35 parejasterritoriales entre 1993y 1999en una parcelade 113km 9 localizadaen lospre Alpesdel centrode Italia. La densidad incremento prog7-esivamentede 28 a 31 parejas/100 km•. Las parejasterritoriales estuvieron dispersas regularmente con una distanciamedia al nido mas cercanamenteocupado de 1108 m (N --- 108). Ochenta y uno pot ciento de los 108 sitiosnidos usadosestaban en cornisas,mientras que el restante 19% estabanubicados en firbolesmadufos. Cada afio, 16-21% de los nidos construidospot gavilanes comunes tornadosen posesi6npot nfilanos negros migratorios (Milvus migrans).La fecha media de posturafue 9 de abril (los primeros = 7 marzo, los mas tardios30 de abril, N = 45). E1tamafio medio de la posturafue 2.32 (N = 19). E1 6xito en la posturafue 91% (N = 33 huevosde 14 nidadas).E1 tamafio medio de la nidada en la posturat•e 2.14 (N = 14). Ochentay nueve pot ciento de las parejas tcrritorialespusieron huevos (N = 37) y 72% sacaronadelante al menosun polluelohasta volant6n (N = 100). E1numero promediodcj6venes volantones fue 1.07 pot parejaterritorial (N = 100), l.ll pot pareja reproductiva(N = 33), y 1.49 pot pareja exitosa(N = 72), sin difercnciassignificativas entre aftos.La dieta fue dominadapot passeriformesmedianos a pequefios,pequefios mamfferos, y culebras. La densidady productividadregistradas rueton comparablesy a menudo mas altas que aquellasrepor- tadaspara otraspoblaciones europeas. La persecuci6nhumana fi•e alta hastalos 70's, actuahnenteno es importante. La futura conversi6nde los bosquecillosj6vencs a bosquesmadufos podria favorecer mayormente alas poblacionespre-alpinas de gavilanescomunes. [Traducci6n de C6sarMftrquez]

• Presentaddress: Raptor ConservationResearch Unit, MuseoTridentino di ScienzeNaturali, Via Calepina14, 38100 Trento, Italy. E4nail address:[email protected]

24 M•CH 2002 BREEDING ECOLOGY 25

The Common Buzzard (Buteo buteo)is one of the wet springsand dry summers (Pinna 1978). Further dc- most abundant European raptors (Bijlsma 1997). tails on the area can be found in Sergio and Boto (1999) Except for a possibledecrease in (Ryttman METHODS 1994), its populations are generally stable or in- Common Buzzards were surveyed between 1993 and creasing, and in some areas still recovering from 1999. We censusedterritorial pairs during the pre-incu- declinescaused by pesticidepoisoning and human bation period, between I February and 15 April, by ob- persecution in the 1950s and 1960s (Taylor et al. servingterritorial displaysand transfersof nest material. 1988,Bijlsma 1997). Factorscurrently limiting den- Common Buzzards typically refurbish many alternate nestseach year,before selectingthe one which they even- sity,productivity, and range expansion,include low tually use (Cramp and Simmons 1980). We put effort availability of food and nest sites, direct persecu- into finding all the active alternate nestsof each pmr tion, and poisoning (Newton et al. 1982, Elliott every year. An alternate nest was defined as active when and Avery 1991, Gibbons et al. 1994, Graham et al. it contained greenery or freshlybroken branchesduring 1995). the preincubation period, and was defined as used when eggswere laid in it. In Italy, the Common Buzzard occurs from sea Whenever possible, nests were visited at least three level to an elevation of 1800 m in the Alps (Canova times: (1) about a week after the mean local laying date 1992). However, despite its abundance and wide to asscssclutch size; (2) just after hatching to estimate distribution, the ' breeding ecology and hatching success,brood size, and hatching date; and (3) when the nestlings were older than 45 d to record the population trends are virtually unknown. The few number of fledgedyoung (nestlingsusually fledge at 50- existing estimatesrefer mainly to the densityof ter- 55 d; Cramp and Simmons1980). Nestswere checkedby ritorial pairs and are usuallybased on low sample climbing the nest tree, descendingcliffs with a rope, or sizes(Canova 1992). In this paper,we present data watchingthe nest from a vantagepoint up the slopewith a 20-60X telescope.To minimize the risk of disturbance, on density,nest spacing,diet, and productivityof nest desertion, or /chick by Black Kites a sedentarypopulation of Common Buzzardsstud- (Milvus migrans)or Ravens(C0rvus corax), only neststhat ied for sevenyears in the Italian pre-Alps. could be checkedvery rapidly were visited during incu- bation/early hatching. Thus, estimates of clutch size, STUDY AREA hatching success,number of laying pairs and brood size representeda subsampleof nests.Hatching date was es- The studyarea is a 113-km2 plot locatedalong the Ital- timated by backdating from the development of ian margin of Lake Lugano, within the central Italian nestlingsfirst observedwhen •<15 d old, by observations pre-Alps (45ø55'N, 8ø50'E). Altitude ranges from 275- at eight focal nests and reference to information con- 1125 masl. The landscapeis characterizedby forested tained in Tubbs (1974), Melde (1976), and Cramp and mountain slopesinterspersed with medium-sizedcliffs Simmons (1980). Laying date was estimated by subtract- and rare patches of herbaceous and scrub vegetation, ing 34 d, the median incubation period (Cramp and Sim- caused by frequent burning. Overall, open areas were mons 1980), from hatching date. Prey remains found •n scarce,mainly due to human modifications,and concen- the nest cup during each nest visit were identified assum- trated on the floors. The area included 16 small ing the minimum possiblenumber of individualsper col- villages,all located on the valley floors. Seventy-oneper- lection event, and by reference to a reference collection cent of the area wascovered by ,13% by urban and information contained in Debtor (1982). areas,9% by water bodies,6% by natural ,and Terminologyfollows Steenhof (1987): a reproductive 1% by farmland. pair is one which laid -->1 egg, a successfulpair is one Dominant tree speciesin the forest included sweet which raised -->1nestling until >45 d old, and breeding chestnut ( Castaneasativa), downy ( Quercuspubescens), successis the percentage of successfulterritorial pairs. A sessile oak (Quercuspetraea), European hop-hornbeam nest area is an area where -->1 alternate nest is found ( Ostryacarpinifolia), and tree (Robiniapseudoaca- within any one year, but where only one pair nestseach cia). Forests were managed for timber production pri- year (Sergio and Boto 1999, Sergio and Bogliani 1999). marily by means of stool shootsregeneration (coppice Statistical Methods. The degree of regularity of nest system;Matthews 1989), with a rotation of 20-30 yr. Ma- dispersion was estimated by means of the G-statistic ture trees were often maintained as single individuals or (Brown 1975), calculated as the ratio between the geo- in small clumps as bearers (coppicewith standards; metric and arithmetic mean of the squared nearest Matthews 1989). However, most of the woodland had neighbor distances(NND) between used nestsand vary- been recently felled and consisted of a homogeneous ing between 0 and 1. Values close to 1 (>0.65) indicate cover of young secondgrowth forest. Some young wood- a regular dispersionof nestsites (Brown 1975). Statistical land patcheswere being converted to mature woodland, significance of the deviation from randomness toward but at the time of study mature forest was still concen- regularity of nest spacing was assessedby means of the trated on a few steep slopes. test proposed by Clark and Evans (1954). To minimize Except for forestry operations, human activitieswere the bias caused by the NNDs of pairs located along the mainly confined to lowlandsand mostlyabsent from the border of the studyarea, we applied the correction sug- mountain slopes.Climate is temperate continental with gestedby Donnelly (1978). Details of mathematicalpro- 26 SER(310ET AL. VOL. 36, NO. 1

Table 1. Density,nest spacing,and regularity of nest dispersionof a Common Buzzard population in the Italian pre-Alps (1993-99). Means are given +SE.

TERRITORIAL MEAN NEAREST PAIRS/100 NEIGHBOR DISTANCE YEAR km 2 (N a) (m) (N) G-STATISTIC z pb 1993 28 (32) 1041 + 98 (16) 0.776 8.9 <0.001 1994 28 (32) 1057 m 132 (15) 0.660 9.1 <0.001 1995 29 (33) 1074 m 108 (17) 0.721 9.5 <0.001 1996 29 (33) 1028 -+ 131 (16) 0.614 9.0 <0.001 1997 29 (33) 1381 _+ 140 (13) 0.785 13.2 <0.001 1998 29 (33) 1082 m 134 (13) 0.696 9.6 <0.001 1999 31 (35) 1134 + 88 (18) 0.818 10.7 <0.001 Total 29 (7) c 1108 m 44 (108) 0.703 8.06 <0.001 Number of territorial pairs censusedin the studyarea each year. Statisticalsignificance of the deviationof nest spacingpattern from randomnesstoward regularity (Krebs 1998). Grand mean for the 7 yearsof study. cedures can be fbund in Krebs (1998). To meet the as- nestsaccounted for 81% of 108 used nest-years, sumptions of normality, NNDs were log½transformed, with no year-to-yearvariation in their frequency of and laying dates were square root transformed prior to parametrictests. All meansare givenwith SE, all testsare occurrence (X2 = 5.53, df = 6, P = 0.48; Table 2). two-tailed, and statisticalsignificance was set at P < 0.05. Of 52 nestswhich were used at least once during the seven years of study, 15 were placed on trees, RESULTS 13 on bare rock ledges,and 24 at the base of trees Density and Nest Dispersion. The number of ter- growingfrom the cliff faces.Of 15 tree nests,seven ritorial pairs increasedfrom 32 to 35 through the were placed on sweetchestnut, two on Scotchpine study period. Density correspondinglyincreased (Pinus silvestris),two on oak (Quercusspp.), and from 28 to 31 pairs/100km 2 (Table1). MeanNND one each on spruce fir (Picea excelsa),Weymouth did not vary significantly among years (ANOVA, (Pinus strobus),common lime (Tilia europaea), F•i,10t= 1.06, P = 0.39), and was on average 1108 and European ash (Fraxinus excelsior).The mean -- 44 m (range = 400-2500 m, N = 108; Table 1). height of these 15 nests on trees was 15 _+ 1 m. The G-statisticindicated a regular dispersion of Five pairs had alternate nests on both cliffs and nest sites in all years except 1996 (Table 1). The trees, and laid eggsin both typesof nestsin differ- spacing pattern significantly deviated from ran- ent years. The mean number of years that a nest domnesstoward regularity in all the study period was consecutivelyoccupied was 1.2 -+ 0.1 for tree (Krebs 1998, Table 1). nests (range = 1-3, N = 15) and 2.1 + 0.3 for cliff Nest Sites. Mean altitude of used nests was 585 nests (range = 1-7, N: 37); the difference be- -+ 16 m (range = 270-870 m, N = 108) and did tween the two was significant (Mann-Whitney U not vary significantlyamong years (P•i,102= 0.43, P test, z = -2.07, P = 0.038). = 0.86). Mean altitude of cliff nests was higher than that of tree nests (608 -- 15 m and 483 _+ 46 Each year, 16-21% of the active alternate nests m, respectivly;Fl,106 = 10.53, P = 0.002). Fourteen were taken over by migratory Black Kites on their to 15 pairs were closelymonitored everyyear until arrival (18 March to beginning of April; Sergioand we were reasonablysure to have detected all their Boto 1999); this percentage did not vary signifi- active alternate nests.On average,these pairs had cantly among years (X2 = 2.88, df = 6, P = 0.82; three activealternate nests (range = 1-7; Table 2), Table 2). To assesswhether Common Buzzards w•th no year-to-yearvariation in their mean num- may have selectedcliff or tree nests,we compared ber (b•3,90= 0.02, P = 1.0). Overall, we censused the frequency of cliff nesting between used nests 377 activealternate nest-years;76% of them were and active alternate nests. We removed all nests positioned on cliffs and 24% on trees,with no sig- taken over by Black Kitesfrom the sampleof active nificant among-year variation in the two propor- alternate nests,as thesewere actually not available tions (X2 = 1.37, df = 6, P = 0.97; Table 2). Cliff to buzzards.There was no significant selectionfor MARCH2002 COMMONBUZZARD BREEDING ECOLOGY 27 28 SERGIOET AL. VOL. 36, NO. 1 cliff or tree nests within any of the seven study Table 4. Diet of breeding Common Buzzardsin the Ital- years(X 2 --<1.71, df = 6, P a 0.19). ian pre-Alps (1993-99), as estimatedby food remains (N Breeding Season. were observed on their = 142) collectedfrom nests.Remains collected during 67 visits to 25 nests. territories all year. Mean laying date did not vary significantly among years (Kruskal-WallisX 2 = 11.15, df = 6, P = 0.08). First egg laying dates NUMBER OF ranged from 7 March to 30 April, averaging9 April PREYC•TEGORY ITEMS (%) (SE = 1.60 d, N = 45). No casesof replacement Birds 66 (46) clutches were observed in any year, even after Blackbird (Turdus merula) 26 (18) breeding failures occurred early in the breeding EurasianJay (Garrulusglandarius) 21 (15) season.The mean date of the first flight of a nes- Others a 8 (6) tling in a brood was 19 June (SE: 2.76 d, earliest Unidentified Passeriformes 11 (8) = 4June, latest = 5 july, N = 14 broods). 41 (29) Productivity. Mean clutch size was 2.32 + 0.13 Common (Talpa europaea) 8 (6) (N = 19). Hatchingsuccess was 91% (N = 33 eggs Muridae spp.b 12 (8) from 14 clutches).Brood size at hatching was2.14 Others t 21 (15) + 0.18 (N = 14). Thirty-three of 37 pairs that were Reptilesd 30 (21) monitored laid eggs,and raised a mean of 1.11 +- c 4 (3) 0.15 young per pair. There was no year-to-yearvar- 1 (1) iation in the percentage of successfulterritorial • Includes: European Robin (Erithacusrubecula) (N = 2), Green pairs (X2 = 5.16, df: 6, P = 0.52; Table 3). Overall (Picus viridis) (N = 2), EurasianSparrowhawk (Ac= breeding successwas 72% (Table 3). The mean cipiternisus) (N = 1), (Dendrocopos number of fledged young per territorial pair was major) (N = 1), Chaffinch (Frin•lla coelebs)(N = 1). 1.07 (Table 3), with no significantamong-year dif- • Includes:Pityrays spp. (N = 2), bankvole (Clethrionomysglareolus) (N = 1), wood mouse (Apodemussylvaticus) (N = 1), yellow ferences (F6m = 1.52, P = 0.18). The mean num- necked mouse (Apodemusflavicollis)(N = 1), housemouse (Mua ber of fledged young per successfulpair was 1.49 musculus(N = 1), unidentified Muridae (N = 5). (Table 3), and did not vary significantly among • Includes: red (Sciurusvulgaris) (N = 4), Crociduraspp. years (F6,65= 1.60, P = 0.16). Causesof failure (N = 1), (Mustelanivalis) (N = 1), (Myoxusglis) (N = 1), brown (Lepuseuropaeus) (N = 1), unidentified were usuallyunknown, apart from two casesof par- mammal (N = 13). tial brood predation by Black Kites, and one case d Includes:western whip (Coluber viridiflavus) (N = 6), Aes- in which a young was electrocutedjust after fiedg- culapian snake (Elaphelong•ssima) (N = 7), unidentified Colu- lng. bridae (N = 11), common wall (Podarcismuralis) (N = 4), The number of fledged young declined with lay- slow (Anguisfragilis) (N = 2). • Inchides:common (BuJobt{]'o) (N = 4). ing date, but not significantly(r = -0.17, N = 44, P = 0.27). There wasno significantcorrelation be- tween the number of fledged young and nest site the availabilityof woodland can be a key factor lim- elevation (r = 0.04, N = 99, P = 0.67) or NND (r iting population density (Dare and Barry 1990, = 0.11, N = 88, P = 0.30). The mean number of Bijlsma 1993, Halley 1993). Cliff nesting does oc- fledged young did not differ between cliff nests cur throughout their range, but generally at low and tree nests(Fl,9S = 0.002, P = 0.97). frequency,and in areaswith limited tree availability Diet. Diet was dominated by birds, mammals, (Dare 1995). In our studyarea, buzzardstended to and reptileswhich accountedfor 46, 29, and 21% selectnest trees within woodland patchesthat were of 142 prey remains collected, respectively,in the more mature than those around random trees (F. nestsof 20 pairs (Table 4). We were able to assess Sergio and C. Scandolaraunpubl. data). Among the age of 36 avianprey individuals:19% werenes- alternate nest sites,no prefbrence was evident be- tlings,72% wererecently fledged juveniles, and 8% tween cliff and tree nests,even though cliff nests were adult individuals. were occupied for higher numbers of consecutive yearsthan tree nests.High frequencyof cliff nest- DISCUSSION ing may have been causedby low availabilityof suf- Eighty-one percent of the nests used for breed- ficiently mature woodland patches, even though •ng in our area were placed on cliffs. In most of single tall trees were relativelyabundant and wide- , Common Buzzards are tree nesters, and spread in the study area. This is consistent with MARCH 2002 COMMON Buzz^}m BREEDING ECOLOGY 29 30 SERGIO E•r ^t.. VoL. 36, No. 1 buzzards responding more to the structural char- Penteriani and Faivre 1997; Table 5). Productivity acteristicsof breeding woodland patches than to wasalso comparableor higher than thosereported the micro-characteristics of individual nesting for other mountainous environments (Dare 1995, trees. Alternatively,cliff nesting may be a response Swann and Etheridge 1995) and for some lowland to the recent history of persecutionand nest rob- areas (Kostrzewa 1996, Dare 1998; Table 5). bing sufferedby the speciesin this area (Bianchi The diet of the studypopulation was diverse,as et al. 1969). From discussionwith local villagers, typical for this species (Cramp and Simmons we know of at least three territories where nestlings 1980), and dominated by birds, small mammals, were regularlycollected up until the 1970s,and we and snakes.We caution that diet analysesbased on have indirect evidence of nest robbing at one easily prey remains tend to overestimatelarge or con- accessiblesite during our study.In a high-perse- spicuousprey speciescompared to analysisof pel- cution area of ,only two tall and inaccessible lets or direct observationsof prey delivered to the tree nests out of seven were not robbed of chicks nest (e.g., Goszczynskiand Pilatowski1986, Red- (Cairone 1982). Cliff nests are generally lessacces- path et al. 2001, Marchesi et al. 2002). However, sible than tree nests to humans and cliffs allow buz- preliminary results of the analysisof 366 pellets zards to place their nestshigher from the ground gave a picture of diet compositionsimilar to that than trees. In our study area, cliff nests were also obtainedby the analysisof remainsin the nest (F. on average at a higher elevation than tree nests, Sergio and C. Scandolaraunpubl. data). Overall, affording additional advantagesin terms of dis- the high frequency of confirmsthe impor- tance from sources of human disturbance, which tance of such prey for Common Buzzardsin Med- are mostly located at low altitude in the valley iterranean countries and at southern latitudes floors. Thus, the interaction between the selective (Cramp and Simmons1980, Haberl 1995). Finally, pressureassociated with potential nestrobbing and the frequent occurrenceof typicalwoodland spe- the low availabilityof mature woodland patches cies in the diet agreed with our many qualitative may causethe local high fi•equencyof cliff nesting, observationsof individualshunting by sit-and-wait a pattern alsoobserved in the local BlackKite pop- tactics within woodland habitats. On such occa- ulation (Sergioand Boto 1999). Each buzzardpair sions, buzzards usually perched on intermediate- had on average three alternate nests, and up to height branchesscanning the forest floor and can- seven, within its nest area. This is in agreement opy for periods of 2-5 min, before moving to with data fi•om other parts of Europe; Tubbs another perch on a nearby tree (pause-traveltactic; (1974) reported an average of 3.2 alternate nests Widen 1994). per nest area (range 1-14) for the of The exploitation of a wide range of habitats,the . In our studyarea, some nests,especially selection of suitable nest sites inaccessible to hu- on cliffs, were used for a number of consecutive mans, and the adoption of a diverseopportunistic years.However, most nestswere used for only one diet allowed Common Buzzards to settle at a rela- or two years.Such frequent nest switchingwas pos- tivelygood densityand reproducesuccessfully with- sibly enhanced by competition with Black Kites, in the heavilywooded landscapeof the central Ital- bnt has alsobeen reported in other Common Buz- ian pre-Alps. The local breeding population was zard populationsfree of such competition (Tubbs stable or slightly increasing in number. No strong 1974, Cramp and Simmons1980). threats were apparent: persecution was sporadic Despite the sporadicpersecution, the observed and the continued successionof coppicewoodland densityand productivitywere in the range of that to mature forest could f•trther increase available reported for other European populations (Table nesting and foraging habitat. The role of habitat 5). In Europe, Common Buzzard breeding densi- availability,weather, diet, and coinpetition with ties peak in areasof lowland traditional farmland Black Kites as potential factorslimiting densityand interspersedwith abundant mature woodlots(Bijls- breeding performance of the local Common Buz- ma 1997). Densityin the Italian pre-Alpswas only zard population is currently under investigation.

slightly lower to that found in such optimal agri- ACKN OWI.EDGMENTS cultural habitats (Bijlsma 1993, Kostrzewa 1996, We thank F. Saporetti, P. Pavan,and W. Guenzani for Dare 1998, Goszczynski1997), and higher than any infi•rming us of the locationof somenests. We thank L published estimate for mountainous areas (Dare Marchesi fi•r the identification of avian prey remains, and and Barry 1990, Halley 1993, Graham et al. 1995, P. Pavan and A. Scandolarafor help with the fieldwork MARCH 2002 COMMON BUZZAm) BREEDING ECOLOGY 31

We thank J.C. Bednarz, M. Donaghy , W. Cres- of Buzzardpersecution 1975-1989. Study38:52- swell, L. Gomulski, J.L. Quinn, C.M. Perrins, and an 56. anonymousreferee for commenting on a first draft of GIBBONS,D., S. GATES,R.E. GREEN,R.J. FULLER,AND R.M the paper. Part of the researchwas funded by the Trento FULLER. 1994. Buzzards Buteo buteo and Ravens Museum of Natural History. coraxin the uplands of Britain: limits to distribution LITERATURE CITED and abundance. Ibis 137:S75-S84. GOSZCZYNSKT,J. 1997. Densityand productivityof Com- AUSTIN,G.E. AND D.C. HOUSTON.1997. The breeding mon Buzzard Buteobuteo and GoshawkAccipitergentzhs performance of the BuzzardButeo buteo in , Scot- populations in Rogtw, Central PolandßActa Ornithol- land and a comparison with other areas in Britain. ogica32:149-155ß Bird Study44:146-154. --AND T. PILATOWSKI. 1986. Diet of Common Buz- BIANCHI, E., L. MARTIRE, AND t. BIANCHI. 1969. Gli uccelli zard (Buteobuteo L.) and Goshawk(AccipitergentilisL) della provincia di Varese (Lombardia). Riv. Ital. Or- in the nesting period. EkologiaPolska 34:655-667ß nitol. 39:384-401. GRAHAM,I.M., S.M. REDPATH,AND S.J. THIRGOOD.1995. BIJLSMA,R.G. 1993. Ecologischeatlas van de Nederlandse The diet and breeding densityof Common Buzzards roofvogels.Schuyt, Haarlem, . Buteobuteo in relation to indices of prey abundance ß 1997. Buzzard.Pages 160-161 in WJ.M. Hage- Bird Study42:165-173. meijer and MJ. Blair [EDS.], The EBCC Atlas of Eu- HABF•RI,,W. 1995. Zum Beutespektrum des MSusebus- ropean breeding birds, their distribution and abun- sards, Buteobuteo (), im Waldviertel (Nm- dance. T. & A.D. Poyser,, U.K. dortsterreich). lz•retta38:124-129. BROWN,D. 1975. A test of randomnessof nest spacing. HALLEY,DJ. 1993ßPopulation changesand territorial dis- WildJbw126:102-103. tribution of Common Buzzards Buteo buteo in the Cen- CAmONE,A. 1982. Successoriproduttivo di Gheppio, Gril- tral Highlands, .Bird Study40:24-30. laio e Poiana nel territorio di Roccapalumba(Sicilia). HENmOUX, P. ANDJ. HENRIOUX.1995. Seize ans d'etude Avocetta 6:35-40. sur les rapaces diurnes et nocturnes dans l'Ouest le- CANOVA,L. 1992. Poiana. Pages569-576 in P. Brichetti, manique (1975-1990). Nos Oiseaux43:1-26. P. De Franceschi and N. Baccetti [EDS.], Fauna HOHMANN,U. 1995. Untersuchungenzur Raumnutzung d'Italia. Edizioni Calderini, Bologna,Italy. und zur Brutbiologie des MSusenbussards(Buteo bu- C•mK, PJ. AND F.C. EVANS.1954. Distance to nearest teo)im Westen Schleswig-Holsteins.Corax 16:94-104. neighbor as a measureof spatialrelationships in pop- KOSTRZEWA,A. 1991. Interspecificinterfkrence compeu- ulations. Ecology35:445-453. tion in three European raptor species.Ethology Ecology CRAMP, S. AND K.E.L. SIMMONS. 1980. Handbook of the & 3:127-143. birds of Europe, the and North . ß1996. A comparativestudy of nest-siteoccupancy Vol. 2. and Bustards. Oxford Univ. Press, Ox- and breeding performanceas indicatorsfor nesting- ford, U.K. habitat qualityin three European raptor speciesßEthol- DARE,PJ. 1995. Breeding successand features ogyEcology & Evolution8:1-18. of BuzzardsButeo buteo in Snowdoniaand adjacentup- KPmBS,CJ. 1998. Ecologicalmethodology. HarperCollins, lands of north . Welsh Birds 1:69-78. New York, NY, U.S.Aß --. 1998. A Buzzard population on Dartmoor, 1955- MARCHESI, L., P. PEDRINI, AND F. SERGIO. 2002. Biases as- 1993. Devon Birds 51:4-31. sociatedwith diet studymethods in the . J --AND J.T. BARRY.1990. Population size,density and RaptorRes'. 36:11-16. regularity in nest spacing of Buzzards Buteobuteo in MATTHEWS,J.D. 1989. Silviculturalsystems. Oxford Univ. two upland regionsof North Wales.Bird Sudy37:23- Press, Oxford, U.K. 29. MELDE, M. 1976. Der MSusebussard. Die Neue Brehm- DEBROT, S. 1982. Atlas des poils de mammiferes Bficherei,Wittenberg Lutherstadt,. d'Europe. Institut de Zoologie de l'Universit• de Neu- NEWTON,I., P.E. DAMS,AND J.E. DAMS.1982. Ravensand chatel, Neuchatel, . Buzzardsin relation to sheep-farmingand forestrym DONNELLY, K. 1978. Simulations to determine the vari- Wales.J. Appl. Ecol.19:681-706. ance and edge-effect of total nearest neighbor dis- PENTERIANI,V. AND B. FAWRE.1997. Breeding density and tance. Pages 91-95 in I. Hodder [ED.], Simulation landscape-level habitat selection of Common Buz- methods in archeology.Cambridge Univ. Press,Lon- zards (Buteobuteo) in a mountain area (Abruzzo Ap- don, U.K. pennines, Italy).J. RaptorRes. 31:208-212. DVORAK, M., A. RANNER, AND H. BERG. 1993. Atlas der PINNA, M. 1978. L'atmosfera e il clima. U.T.E.T., Torino, Brutvtgel6sterreichs. Bundesministerium ffir Urn- Italy. welt, Jugend und Familie. Wien, Austria. REDPATH,S.M., R. CLARKE,M. MADDERS,AND S.J. THIR- EI,LIOTT,G.D. AND M.I. AVERY.1991. A review of reports GOOD.2001. Assessingraptor diet: comparing pellets, 32 S•;RG•O•;T AL. VOL. 36, No. 1

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