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1 December 2007 Prey Size Selection of Insular Lizards by Two Sympatric Predatory Bird Species
David P. Padilla, Manuel Nogales, Patricia Marrero
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Size-related selection of insular lizards by two sympatric predatory bird species (Southern Grey Shrike and Eurasian Kestrel) was studied in an arid insular environment. The endemic lizard genus Gallotia was a key resource in the diet of both predators, constituting more than 50% of the total biomass. Shrikes captured smaller lizards than kestrels during all seasons (mean snout - vent length (SVL): 7.4 ±1.9 vs. 9.4 ± 2.1 cm respectively), presenting a sequential use of lizard sizes and avoiding potential competition. On the other hand, shrikes and kestrels showed the same seasonal variation pattern, capturing the largest lizards during their breeding periods (spring). Considering lizard availability, shrikes displayed less selective predation than kestrels in all seasons. Shrikes positively selected the medium lizard size (SVL: 5–10 cm) during the nestling period, but negatively selected the small lizard size (SVL: < 5 cm) in autumn and winter, probably due to an explosion of juvenile lizards. Lastly, kestrels appeared to be more selective, negatively choosing the small lizard size but positively selecting the largest ones all the year round (SVL: > 10 cm).



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David P. Padilla, Manuel Nogales, and Patricia Marrero "Prey Size Selection of Insular Lizards by Two Sympatric Predatory Bird Species," Acta Ornithologica 42(2), 167-172, (1 December 2007).
Received: 1 July 2007; Accepted: 1 October 2007; Published: 1 December 2007
Canary Islands
Falco tinnunculus
feeding ecology
Gallotia galloti
Lantus meridionalis
prey selection
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