Bird Study (2012) 59, 207–217 Habitat preferences of Bonelli’s Eagles Aquila fasciata in Sicily MASSIMILIANO DI VITTORIO1, MAURIZIO SARA` 1 and PASCUAL LO´ PEZ-LO´ PEZ2∗ 1Department of Environmental Biology and Biodiversity, University of Palermo, Via Archirafi 18, 93100 Palermo, Italy and 2Vertebrate Zoology Research Group, Instituto Universitario de Investigacio´n CIBIO, University of Alicante, Campus San Vicente del Raspeig, Edificio Ciencias III, 03080 Alicante, Spain Capsule For breeding, areas dominated by extensive agricultural and rugged Mediterranean landscapes are preferred; maintenance of habitat heterogeneity and extensive agriculture are key for the conservation of this eagle. Aims To model breeding habitat preferences of Bonelli’s Eagles Aquila fasciata in Sicily, where the last viable population still remains in Italy, in order to identify the most important habitats for conservation. Methods Pairs were monitored between 1990 and 2010. A case-control design through GLMs was used at two spatial scales: landscape and home-range. Variables included topographic, climatic, land-use, road and descriptors of habitat heterogeneity. Information-based criteria were used to select the best subset of predictors. Results A total of 22 breeding pairs are still breeding, which represent about the 90% of the Italian popu- lation. The best models at both scales showed that Bonelli’s Eagles were clearly associated with Mediterra- nean features, including rugged areas surrounded by extensive arable land, shrubland and herbaceous vegetation. Our results emphasize the negative effects of habitat fragmentation and agricultural intensifica- tion on the probability of occurrence of Bonelli’s Eagles. Conclusion The distribution of Bonelli’s Eagles in Sicily can be described by a relatively small number of topographical and land-use variables. The maintenance of habitat heterogeneity is key for the conservation of this endangered raptor. The knowledge of species distribution patterns and the programmes (Larson et al. 2004, Lo´pez-Lo´pez et al. identification of factors influencing these patterns are 2006, Lo´pez-Lo´pez et al. 2007a, Nams et al. 2006). crucial in conservation biology (Channell & Lomolino In the case of Bonelli’s Eagles Aquila fasciata, model- 2000, Whitfield 2005). In recent years, owing to the ling procedures aimed at identifying relationships broad use of geographical information systems (GIS), between habitat features and species occurrence have the modelling of species distributions has been increas- been largely used to model the species’ distribution, Downloaded by [T&F Internal Users], [Mr Susan Cullen] at 12:10 11 May 2012 ingly used to identify suitable habitat and to predict mainly in Spain, where it has its main stronghold in potential distribution (Robertson et al. 2003, Europe (Bustamante & Seoane 2004, Ontiveros & Rushton et al. 2004). Predictive models have been Pleguezuelos 2003, Mun˜oz et al. 2005, Lo´pez-Lo´pez used in many different fields of conservation, with par- et al. 2006, Lo´pez-Lo´pez, Garc´ıa-Ripolle´s & Urios ticular emphasis on the investigation of threatened 2007, Niamir et al. 2011). In addition, habitat selec- species (Guisan & Zimmermann 2000). Furthermore, tion studies have been focused to account for the predictive distribution models have important poten- influence of habitat composition on population tial applications as they can forecast species occurrence density and productivity (Carrete et al. 2000) or to in poorly documented areas, predict the response of a test the effect of climate on productivity (Ontiveros species to changes in land-uses or environmental con- & Pleguezuelos 2003). ditions, or reveal adequate focal areas for conservation The fact that ecological patterns depend on the spatial scale at which they are analyzed (Levin 1992, ∗Correspondence author. Email: [email protected] Graf et al. 2005) has become axiomatic, and Q 2012 British Trust for Ornithology 208 M. Di Vittorio, M. Sara` and P. Lo´pez-Lo´pez predictive models investigating habitat preferences of METHODS species of conservation concern usually employ a Study area multi-scale approach to identify the different factors affecting habitat preferences (Johnson 1980, Store & Sicily is the largest Mediterranean island (extension ¼ Jokima¨ki 2003). Bonelli’s Eagle populations are 25.414 km2) (Fig. 1). Almost 24.4% of the territory is affected not only by local habitat characteristics but mountainous, 61.4% corresponds to highlands whereas also by historical and environmental factors that are 14.2% of the surface is lowland. Forests and Mediterra- often human-related, which act on larger geographical nean vegetation, of which almost 6% burns every year, scales, and the choice of a suitable habitat is probably cover 8.4% of the surface (Agenzia per la protezione del- the result of the integration of different choices at l’ambiente e per i servizi tecnici [APAT] 2005). The different scales (Mart´ınez et al. 2003, Lo´pez-Lo´pez island is also one of the most populated in the western et al. 2006). Mediterranean (195 inhabitants per km2). There is Bonelli’s Eagles are large-size raptors whose western habitat heterogeneity in areas where cultivation zones Palaearctic population is distributed mainly within the (especially arable land) alternate with forest patches of circum-Mediterranean area, from Morocco, Algeria non-native species (Pinus spp. and Eucalyptus spp.), and Tunisia, to southern France, Spain, Portugal and natural woodland (Quercus spp.) and Mediterranean southern Italy (Cramp & Simmons 1980). In recent vegetation. years this species has suffered a severe population decline in most of its European range (BirdLife Inter- Censuses and study design national 2004), and has been listed as endangered in Europe (BirdLife International 2011). In Italy, Bonelli’s We monitored Bonelli’s Eagles from 1990 to 2010, Eagles were recorded in the main islands and in the counting 36 different breeding territories, 22 of which southern Apennines (Cortone & Mirabelli 1984, Hage- were regularly occupied (i.e. those with presence of indi- meijer & Blair 1997). However, current reproduction in viduals showing courtship behaviour, breeding attempts the southern Apennines has not been confirmed and and chick-rearing during at least 75% of the study dur- only rare observations have been made in recent years ation). All territories were visited at least three times (Cortone & Di Vittorio, pers. obs.). Although this during each breeding season. A case-control design was species was also historically fairly abundant in Sardinia used for modelling (Hosmer & Lemeshow 2000, (Arrigoni degli Oddi 1929), it started decreasing in the Keating & Cherry 2004). We used two different spatial 1960s, and only three or four pairs remained in the late scales: (1) a ‘landscape’ scale, encompassing the 10 × 1970s (Lo Valvo & Massa 1992). Currently, it might be 10 km universal transversal Mercator (UTM) squares still present but there is no certain proof of reproduc- where the species was present or absent; and (2) a tion (Schenk, pers. comm.). In Sicily, Bonelli’s Eagles ‘home-range’ scale based on the spatial distribution of were regularly recorded as breeders since the 19th territories centred on nest-sites. At the landscape scale, century (Doderlein 1869–74, Massa & Schenk 1983). 83 occupied UTM squares were compared with 205 In the 1960s, the species disappeared from southeast unoccupied squares, including bioclimatic, ecological Sicily (Iblean plateau) owing to heavy poaching. and land-use factors (Table 1). At the home-range Apart from this local decrease, the Sicilian population scale, we compared the specific habitat composition Downloaded by [T&F Internal Users], [Mr Susan Cullen] at 12:10 11 May 2012 seemed apparently stable. In the mid-1980s, surveys and topographic factors of those 22 regularly occupied recorded 17 breeding pairs (Massa 1985). At present, territories versus the same number of unoccupied terri- the species breeds regularly in 22 known breeding terri- tories randomly selected. tories (Di Vittorio 2007), representing nearly 90% of the entire Italian population (25–28 estimated pairs [Di Vittorio unpub. data]). However, the corresponding Measurement of habitat variables at the landscape scale density of 1 pair/1155 km2 is much lower than that reported in other European countries (Carrete et al. The presence/absence of Bonelli’s Eagles in UTM 2002, Balbont´ın et al. 2003). squares was obtained from the Atlas of Biodiversity In the present study we have focused on the Bonelli’s of Sicily (ARPA Sicilia 2008) and specific field Eagle population that remains in Sicily, with the aim of surveys (Fig. 1). We used UTM squares because they modelling habitat preferences to identify the predictors are a common reference in ornithological studies of suitable areas for conservation. (Ontiveros 1999, Mart´ınez et al. 2003, Sara` 2008), Q 2012 British Trust for Ornithology, Bird Study, 59, 207–217 Bonelli’s Eagle habitat preferences 209 Figure 1. Distribution of Bonelli’s Eagle pairs in Sicily, southern Italy. The 10 × 10 km Universal Transversal Mercator squares where the species is present are depicted in grey; location of Sicily within Italy is shown on the inset map. allowing comparisons with other study areas. The Measurement of habitat variables at the home-ranges of the currently breeding pairs (n ¼ 22) home-range scale ¼ and those recently abandoned (n 14) fell within Nest-sites and randomly selected unoccupied points were 83 UTM