Abstract
Several species of birds deliberately drop hard food items, such as walnuts and molluscs, from high places to break the shell and eat the content. Although the carrion crow Corvus corone preys on the introduced apple snail Pomacea canaliculata by directly breaking the shells with their beaks in paddy fields in Japan, snails living in ponds are too large and hard for crows to directly break the shells. We found that carrion crows dropped apple snails in and around dried ponds in winter in Marugame, Kagawa, Japan, and conducted detailed observations on their predation behaviour. The crows dropped the snails onto various substrates in and around Hachijo Pond, and the release point was higher when the substrate was wet mud than when it was concrete, rock, or grass. As carrion crows rarely prey on other freshwater snails in Japan, this foraging behaviour has likely developed since the introduction of apple snails in the 1980s. The intense predation by the crows likely reduced the snail density in this reservoir pond.
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Acknowledgements
We thank our laboratory members at Nara Women’s University for the discussions and assistance and Dr. Takashi Y. Ida for help in statistical analyses. We also thank the management staff of Hachijo Pond for allowing us to conduct this study.
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This work was supported by the Sasakawa Scientific Research Grant from The Japan Science Society.
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Supplementary file1 Video 1. Apple snail dropping and rolling by carrion crows in Kagawa, Japan. (a) Apple snail dropping by a carrion crow, (b) shell rolling by a crow without flight (twice), (c) shell rolling by a crow with (1st time) and without (2nd time) flight. Video by Haruka Uehara. (MP4 266673 KB)
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Uehara, H., Yoshimura, M. & Yusa, Y. Dropping of apple snails (Pomacea canaliculata) by carrion crows (Corvus corone). J Ethol 42, 107–114 (2024). https://doi.org/10.1007/s10164-024-00808-6
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DOI: https://doi.org/10.1007/s10164-024-00808-6