Abstract
The diet of Short-toed Snake-eagle (Circaetus gallicus) during the breeding season in an area dominated by cork and holm oak parkland forests (Montados) was analyzed in this study. As expected, results showed that snakes are the dominant prey in the diet of this eagle, comprising up to 92.5% of the identified items, if potential secondary prey species were excluded. The Montpellier Snake (Malpolon monspessulanus) was the most consumed one (42.2%), followed by the Ladder Snake (Zamenis scalaris) (28.0%), and the water snakes (Natrix spp.) (14.2%). According to the same criteria, lizards (mainly Psammodromus algirus) and mammals represent between 4.8 and 2.2%, respectively. Other animals such as pond turtle and amphibians are irregular prey (<1%), and no bird remains were found at all. Short-toed Snake-eagle is usually referred as a stenophagic predator where snakes are by far its most important prey type, and where within this taxonomic group it behaves as a generalist predator. In this study this premise was then tested comparing the relative abundance of the snake species with their proportion in the diet composition of the eagle in order to know whether or not prey selection exists with regard to the species of snakes in this region. Results point to a quite plausible "preference" for the Ladder Snake and an "avoidance" for the smooth snakes group (Macroprotodon brevis/Coronella girondica), and possibly for the Horseshoe Whip (Hemorrhois hippocrepis). The avoidance to the Horseshoe Whip must be indirect and habitat related, while in relation to the two smooth snakes it may be due in large extend to its small size, in particular.
Highlights
IntroductionThe diet of the Short-toed Snake-eagle (hereinafter called Snake-eagle) is well known and described in several parts of its breeding distribution in the Western Palearctic (BOUDOINT, 1953; GALUSHIN, 1959; THIOLLAY, 1968; CHOUSSY, 1973; BRUNO and PERCO, 1980; MEIR, 1980; GLUTZ VON BLOTZHEIM et al, 1989; CATTANEO and PETRETTI, 1992; del HOYO et al, 1994; VLACHOS and PAPAGEORGIOU, 1994; CAMPORA and ALBERTI, 1997; BAKALOUDIS et al, 1998; CRAMP, 1998; JEDRZEJEWSKA and JEDRZEJEWSKI, 1998; BÉRES, 2007; DARAWSHI, 2009; PETRETTI, 1988, 2012; BAKALOUDIS and VLACHOS, 2011a, 2011b; IVANOVSKY and SHAMOVICH, 2011; MAUMARY et al, 2013; MALAFOSSE and MALAFOSSE, 2015;), including some locations in Iberian Peninsula (VALVERDE, 1967; IRIBARREN and RODRÍGUEZ-ARBELOA, 1973; GARZÓN, 1974; AMORES and FRANCO, 1981; GIL and PLEGUEZUELOS, 2001; PLEGUEZUELOS and ONTIVEROS, 2011), but there is no information from Portugal so far
Prey selection was already noted by BOUDOINT (1953), in Saint-Etienne, France, who stated that vipers and the Green Whip Snake were disproportionally captured according to his observations, the vipers being less captured and the Green Whip Snake more than its availability, and by VALVERDE (1967), in Doñana, Spain, which says that the Lataste's Viper (Vipera latastei) is captured much less often than expected
MEIR (1980), JEDRZEJEWSKA and JEDRZEJEWSKI (1998) and BAKALOUDIS and VLACHOS (2011a, 2011b), who studied the diet of the Snake eagle based only on pellets and prey remains, took into account insect/invertebrates as part of the diet composition
Summary
The diet of the Short-toed Snake-eagle (hereinafter called Snake-eagle) is well known and described in several parts of its breeding distribution in the Western Palearctic (BOUDOINT, 1953; GALUSHIN, 1959; THIOLLAY, 1968; CHOUSSY, 1973; BRUNO and PERCO, 1980; MEIR, 1980; GLUTZ VON BLOTZHEIM et al, 1989; CATTANEO and PETRETTI, 1992; del HOYO et al, 1994; VLACHOS and PAPAGEORGIOU, 1994; CAMPORA and ALBERTI, 1997; BAKALOUDIS et al, 1998; CRAMP, 1998; JEDRZEJEWSKA and JEDRZEJEWSKI, 1998; BÉRES, 2007; DARAWSHI, 2009; PETRETTI, 1988, 2012; BAKALOUDIS and VLACHOS, 2011a, 2011b; IVANOVSKY and SHAMOVICH, 2011; MAUMARY et al, 2013; MALAFOSSE and MALAFOSSE, 2015;), including some locations in Iberian Peninsula (VALVERDE, 1967; IRIBARREN and RODRÍGUEZ-ARBELOA, 1973; GARZÓN, 1974; AMORES and FRANCO, 1981; GIL and PLEGUEZUELOS, 2001; PLEGUEZUELOS and ONTIVEROS, 2011), but there is no information from Portugal so far. GIL and PLEGUEZUELOS (2001) found that the Short-toed Snake-eagle in Granada, Spain, consumes the species of snakes according to their availability in the wild and suggest that this eagle is a trophic generalist within upon the ophidians. PETRETTI (1988) says that in Italy the Green Whip Snake (Hierophis viridiflavus) is the most common snake in the diet of the Snake-eagle and at the same time the more abundant, and MAUMARY et al (2013) suggest that the Snake-eagle is able to adapt its behavior according to the more abundant or accessible species of snakes. Prey selection was already noted by BOUDOINT (1953), in Saint-Etienne, France, who stated that vipers and the Green Whip Snake were disproportionally captured according to his observations, the vipers being less captured and the Green Whip Snake more than its availability, and by VALVERDE (1967), in Doñana, Spain, which says that the Lataste's Viper (Vipera latastei) is captured much less often than expected
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