Seasonal Diet of the Grey HeronArdea cinereaon an Oceanic Island (Tenerife, Canary Islands): Indirect Interaction with Wild Seed Plants

Abstract

A total of 7 460 prey items were counted in the 199 pellets analysed, of which 96.2% corresponded to arthropods. Aeshnidae larvae (Odonata) made up 66.1% of total prey items and were the main invertebrate group. Vertebrates constituted 3.8%, while reptiles and mammals were the main prey (1.8%, respectively). Despite the small size of the invertebrates, this group reached > 60% in terms of biomass. All main prey items varied significantly among seasons. Odonata was the most important group for all seasons, reaching its maximum value in summer. In the case of vertebrates, reptiles were mainly captured in spring and mammals in winter. With regards to indirect interaction with seeds, a total of 901 seeds associated with lizard remains were found in 77 pellets; indicating that they were previously consumed by these reptiles. External visual damage of seeds was low and only 1.1% was destroyed. No seeds germinated after the four month germination experiment and practically all of them were unviable. In conclusion, these results indicate that Grey Heron diet on islands varies in comparison with continental zones, includ- ing an important number of invertebrates and reptiles. Furthermore, this bird acts as an opportunistic secondary seed disperser, although its ecological effect does not seem to be very significant for the dynamics of the Canarian ecosystems.