J. Raptor Res. 26(4):235-238 ¸ 1992 The Raptor ResearchFoundation, Inc.
SEASONAL AND SEXUAL VARIATION IN THE DIET OF THE COMMON BUZZARD IN NORTHEASTERN SPAIN
SANTI MA•IOSA Departamentde Biologia Animal, Universitat de Barcelona, 08028 Barcelona, Spain
PEDROJ. CORDERO ConsejoSuperior de Investigaciones Cient[ficas, Instituto Pirenaico de Ecolog[a, Apartado202, 50080 Zaragoza,Spain
ABSTRACT.--Weexamined the diet of Common Buzzards (Buteo buteo) from a Mediterranean area (Catalonia,NE Spain), by analyzingprey remainsand pelletsfound in the nest,and stomachcontents. The diet was seasonal.Relatively large items, such as young rabbits and OcellatedLizards (Lacerta lepida),predominated in the breedingseason, orthopterans and mantodeansin autumnand insects,rodents and soricidansin winter. Males presentedan empty stomachmore oftenthan females,but only small differences were found in the diet of males and females.
RESUMEN.--Seanaliza la variaci6nestacional en la dieta del ratonerocomfin (Buteo buteo) en una zona mediterrfinea(Catalufia, NE Espafia)a basede restosde presasy egagr6pilasencontrados en los nidos y al analisisde contenidosestomacales. La dietavari6 estacionalmente. Durante el periodoreproductivo, el ratoneroconsumi6 presas relativamente grandes, tales como gazapos y lxgartos,mientras queen otofio consumi6preferentemente ort6pteros y mfintidos. En inviernolos insectos, roedores y musarafias constitu- yeronla basede la dieta.Los machos presentaron el est6magovaclo con mayor frecuencia que las hembras pero s61ose detectaronpequefias diferencias en la dieta de ambossexos.
The Common Buzzard (Buteo buteo) feeds on a RESULTS AND DISCUSSION wide rangeof prey,mainly rodents,but alsoon other Diet During the Breeding Season(Spring- vertebratesand invertebratesof appropriate size Summer). EuropeanRabbit (Oryctolaguscuniculus) (Cramp and Simmons1980). Its diet hasbeen stud- was the mostfrequent prey species(Appendix 1). ied in most parts of its geographicalrange, and it This has been found in other Mediterranean areas reflectsunderlying differences in prey availability (Veiga 1982, Real 1987) but is unlike the deciduous (Bustamante1985). However, seasonalvariation has forestregion of Northern Spainwhere invertebrates receivedmuch less attention, probably becauseof form the bulk of the diet (Bustamante1985). The difficultyin studyingthe diet outsidethe breeding CommonBuzzard captured mainly youngrabbits, season.In this paper we investigatethe seasonal veryabundant in springand summer (Soriguer 1981). variation of the diet of the Common Buzzard in a The mean tarsus length of the rabbits taken was Mediterraneanarea, where the speciesis present 37.5 mm (SD = 5.7, range = 26-64, N = 122), throughoutthe year. whichcorresponds to a meanweight of lessthan 550 STUDY AREA AND METHODS g (Mafiosa1991). The secondmost consumed prey Diet outsidethe breedingseason was studiedby ana- were reptiles, especiallyOcellated Lizard (Lacerta lyzing the stomachcontents of 69 CommonBuzzards con- lepida), also very commonin spring and summer fiscated from hunters in the Mediterranean area of Cat- (Castilia 1989). Severalspecies of birds formed an alonia(NE Spain)between October and February of 1982- 87 The sexof 39 individualswas identified.Diet during important percentageof the diet. Invertebrates,am- the breedingseason was studiedin La Segarracounty of phibians,rodents and shrewswere taken only oc- Cataloniaby collectingprey remainsand pelletsfrom 20 casionally(Table 1). nests,during and after reproductionin 1985-89. Pellets Diet Outside the Breeding Season.Only 45 were especiallyuseful to identify small prey, which are (65%) of the 69 stomachsanalyzed contained at least rarely found as items in the nest (Mafiosa 1991, Real 1991). The importanceof eachprey was expressedas the one prey. A total of 240 prey items were found percentageof appearanceof that preyamong all preyitems (Appendix1). Insectswere the mostfrequent prey in nests,pellets or stomachs. both in autumn and winter (Table 1). Rabbitswere
235 236 SANTI MA•OSA AND PEDROJ. CORDERO VOL. 26, NO. 4
Table 1. Diet of CommonBuzzard in Catalonia (NE Spain) expressedin percentages.Autumn includesOctober- November,winter December-Februaryand springand summerthe breedingseason.
SPRINGAND SUMMER AUTUMNAND REMAINS PELLETS AUTUMN WINTER WINTER
Mammals 69.90 49.75 7.28 38.2 18.74 Shrews 0.33 0.00 0.00 15.73 5.83 Rabbits 66.55 21.89 0.66 2.25 1.25 Voles 0.00 6.47 3.31 6.74 4.58 Mice 1.34 5.47 1.32 10.11 4.58 Other mammals 1.67 15.92 1.99 3.37 2.50 Birds 16.50 12.44 0.00 3.37 1.25 Reptiles 13.88 35.82 3.31 3.37 3.33 Amphibians 0.17 0.00 0.66 7.87 3.33 Insects 0.00 1.99 87.42 43.82 71.26 Mantodeans 0.00 0.00 31.79 17.98 26.67 Orthopterans 0.00 1.49 54.97 19.10 41.67 Goleopterans 0.00 0.50 0.66 6.74 2.92 Other invertebrates 0.00 0.00 1.32 3.37 2.08 Total 598 201 152 88 240 taken only occasionally,and rodentsand shrewswere stomachcontents, eliminating by this way the bias. the most commonmammalian prey. Becauseof the associatedwith preyremain collections. On grouping low temperatures,reptiles are not availableduring prey into invertebrates,amphibians, reptiles, birds, the autumn and winter periods(Castilia 1989), and rabbits and small mammals, we found differences their presencein the diet was restricted.In winter, betweenbreeding-season, autumn and winter diets most insect populationsdecrease, and small mam- (X2 = 341.436, df = 10, P < 0.01; Table 1). Buzzards mals (rodentsand shrews)increase in their impor- consumedbigger prey during the breeding season tancein the diet. Then they are especiallyabundant than outsideit, but it is possiblethat adults carried in open fields, where they lack coveras they feed. only large prey to the nestsand consumedsmall prey Amphibians increasedtheir presencein the winter themselves,as was observedin other raptors (Veiga diet, when they concentratearound their breeding 1982, Donfizar 1988). This possibility should be pools(Valverde 1967). taken into account when interpreting our results. Seasonaland Sexual Comparison. Compared The sex ratio of buzzards killed did not differ sig- with pellet analysis,collections of prey remains in nificantlyfrom unity (20 malesand 19 females;x 2 nestsunderestimates small preys (invertebrates, small = 0.026, P > 0.05) with no variation between au- mammalsand reptiles). On groupingprey into in- tumn and winter (X2 = 0.779, P > 0.05). Data from vertebrates,poikilotherm vertebrates, birds, rabbits, and small mammals, differenceswere significant(X 2 = 199.038, df = 4, P < 0.01; Table 1). We analyzed Table 3. Number of Common Buzzard stomachs in which seasonalvariation by comparing pellet data with different prey were found in relation to sex.
MALES FEMALES Table 2. Frequencyof full comparedto empty stomachs (N=9) (N= 17) accordingto sex of Common Buzzards. Invertebrates 5 8
MALES FEMALES TOTAL Amphibians 3 0 Reptiles 1 2 Full 9 17 26 Birds 1 1 Empty 10 3 13 Rabbits 0 2 Total 19 20 39 Small mammals 8 10 DECEMBER 1992 SEASONAL DIETS OF COMMON BUZZARDS 237 both seasonscould therefore be pooled to analyze Linnaeus, 1758) a la Segarra.Tesis doctoral,Univer- differencesin diet betweenthe sexes.Empty stom- sitat de Barcelona,Barcelona, Spain. achs were found more often in males than females MARQUISS,M. 1980. Habitat and diet of male and fe- male Hen Harriers in Scotland in winter. British Birds (X2 = 6.278, P < 0.025; Table 2). Although sample 73:555-560. sizeswere small, we found amphibiansmore often --AND I. NEWTON. 1982. Habitat preference •n in stomachsof males than females (Fisher exact test male and female Sparrowhawks Accipiter nisus.Ibis P = 0.03) and Rabbits were taken only by females 124:324-328. (Table 3). These differencesmay be related to the NEWTON,I. 1979. Populationecology ofraptors. T. and sexual dimorphismof the species(male weight = A.D. Poyser,Berkhamsted, U.K. 828 g, femaleweight = 1052 g; Cramp and Simmons 1986. The sparrowhawk.T. and A.D. Poyser, 1980) and can be explainedeither by prey selection Calton, U.K. or by habitat partitioning,as shown in Hen Harriers REAL,J. 1987. L'organitzaci6d'una comunitat de rapin- (Circuscyaneus; Newton 1979, Marquiss 1980), Eu- yairesa la Catalunyamediterrfinea. I: Accipitriformes ropeanSparrowhawks (Accipiter nisus; Marquiss and i Falconiformes.Unpubl. report. Caixa de Barcelona, Barcelona, Spain. Newton 1982, Newton 1986), or American Kestrels 1991. L'filiga perdiguera Hieraaetusfasciatusa (Falcosparverius; Smallwood 1987, 1988). Catalunya:status, ecologia tr6fica, biologiareproduc- tora i demografia.Tesis doctoral,Universitat de Bar- ACKNOWLEDGMENTS celona, Barcelona, Spain. We are grateful to Sheila Hardie for improving the SMALLWOOD,J.A. 1987. Sexual segregationby habitat English of the manuscript.We are also very grateful to in American Kestrels wintering in south-centralFlor- J.E. Jim•nez and R. Kenward for their usefulcomments ida: vegetativestructure and responsesto differential of an early versionof our manuscript. prey availability. Condor89:842-849. 1988. A mechanismof sexual segregationby LITERATURE CITED habitat in American Kestrels (Falco sparverius)win- BUSTAMANTE,J.M. 1985. Alimentaci6ndel ratonero tering in south-centralFlorida. Auk 105:36-46. comfin (Buteobuteo) en el norte de Espafia. Dor•ana SORIGUER,R.C. 1981. Biologlay dinfimicapoblacional Acta Vertebrata 12:51-62. de una poblaci6nde conejos(Oryctolagus cuniculus, L) CASTILLA,A.M. 1989. Autoecologladel lagartoocelado en Andalucfa occidental. Dor•ana Acta Vertebrata 8(3) (Lacertalepida). Tesis doctoral, Universidad Aut6noma VALVEROE,J.A. 1967. Estructurade una comunidadde de Madrid, Madrid, Spain. vertebradosterrestres. Consejo Superior de Investiga- CRAM?, S.C. AND K.E.C. SIMMONS lEDS.]. 1980. The cionesCientificas, Madrid, Spain. birdsof thewestern Palearctic. Vol. 2. Oxford University VEIGA,J.P. 1982. Ecologlade las rapacesde un ecosiste- Press, Oxford, U.K. ma de montafia. Aproximaci6n a su estructura co- DONAZAR,J.A. 1988. Variacionesen la alimentaci6n munitaria. Tesis doctoral, Universidad Complutense entre adultos reproductoresy pollos del Buho Real de Madrid, Madrid, Spain. (Bubo bubo). Ardeola 35:278-284. MAI•OSA,S. 1991. Biologia tr6fica, fis de l'hfibitat i biologiade la reproducci6de Fastor(Accipiter gentilis, Received5 December 1991; accepted20 August 1992 238 SANTIMA•IOSA AND PEDRO J. CORDERO VOL. 26, No. 4
Appendix1. Preyitems of the CommonBuzzard during the breedingand non-breeding season in Catalonia(NE Spain).Species with lessthan fiverepresentatives are groupedin the "other"category.
BREEDING SEASON
REMAINS PELLETS FALL AND WINTER
N % N % N %
Mammals 416 69.60 100 49.75 445 18.75 Crocidura russula 2 0.33 11 4.58 Oryctolaguscuniculus 398 66.55 44 21.89 3 1.25 Sciurusvulgaris 4 0.67 15 7.46 Microtus duodecimcostatus 13 6.47 11 4.58 Apodemussylvaticus 6 1.00 11 5.47 7 2.92 Other a mammals 6 1.00 2 1.99 7 2.92 Unidentified small mammals 15 7.46 6 2.50 Birds 96 16.05 25 12.44 3 1.25 Alectorisrufa 30 5.02 1 0.42 Colurnbapalurnbus 15 2.51 Garrulusglandarius 11 1.84 Unidentified Passeriformes 12 2.01 17 8.46 Other a birds 12 2.01 2 0.83 Unidentified birds 16 2.67 8 3.98 Reptiles 83 13.88 72 35.82 8 3.33 Psarnrnodrornusalgirus 7 1.17 24 11.94 Lacertalepida 44 7.36 25 12.44 Ophidians 31 5.18 8 3.98 I 0.42 Othera reptiles 1 0.17 7 2.92 Unidentified reptiles 15 7.46 Amphibians 1 0.17 8 3.33 Bufosp. 5 2.08 Othera amphibians 1 0.17 3 1.25 Arthropods 4 1.99 175 72.92 Mantisreligiosa 64 26.67 Grillotalpagrillotalpa 13 5.42 Unidentified Acrididae 5 2.08 Other orthopterans 3 1.49 6 2.50 Coleopterans 1 0.50 7 2.92 Othera arthropods 4 1.67 Anelids 1 0.42 Oligochets 1 0.42 Total prey 598 201 240 Otherprey items include: Mammals: Suncus etruscus, Eliomys quercinus, Rattus rattus, Mus spretus, Mus sp., Unidentified Muridae, Mustelanivalis. Birds: Columba oenas, Otus scops, Athene noctua, Alaudidae, Saxicola torquata, Turdus merula, Turdus viscivorus, Oriolus oriolus,Sturnus vulgaris, Fringilla coelebs, Emberiza cidus, Miliaria calandra, Nestling Passeriforme. Ophidians: Malpolon monspessulanus, Elaphescalaris, Unidentified Ophidians. Reptiles: Podarcis hispanica, Blanus cinereus, Natrix natrix, Natrix sp., Anguis fragilis, Vipera latastii.Amphibians: Bufo calamita, Hyla meridionalis, Rana perezi. Coleopterans: Tenebrionidae, Carabidae, Timarcha tenebricosa, Cetoma aurata,Geotrupes stercorarius, Unidentified Coleopterans. Orthopterans: Gryllus campestris, Oedipoda sp., Anacridium sp., Unidentified Orthopterans.Arthropods: Camponotus cruentatus, Lepidoptera Larvae, Disdera sp., Unidentified Isopoda.