Prey ecology and behaviour affect foraging strategies in the Great Cormorant |
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Authors: | Mauro Cosolo Enrico A Ferrero Stefano Sponza |
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Institution: | (1) Department of Life Sciences, University of Trieste, via Giorgieri 9, 34127 Trieste, Italy |
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Abstract: | The fine link between a particular dive pattern and a specific prey item represents a challenging task in the analysis of
marine predator–prey relationships. There is growing evidence that prey type affects diving seabirds’ foraging strategies,
dive shapes and underwater activity costs. This study investigates whether a generalist diver, the Great Cormorant Phalacrocorax carbo, modifies the time budget allocated to prey-capture behaviour and breathing strategies (reactive vs. anticipatory) with respect
to the prey type (pelagic vs. benthic). Video recordings of 91 Great Cormorants show how the ecology and behaviour of their
main prey, Mullets (Mugilidae) and Flounders Platichthys flesus, affect dive/surface durations and the diving pattern. The demersal habit and the low mobility of Flounders leads to an easy
access to prey with an anticipatory strategy. Moreover, the patchy distribution of this fish species increases prey-capture
rates. Conversely, Mullets exploit the whole water column and are highly mobile, and this is reflected in the need of performing
two sequential dives to capture a prey, both longer and likely more expensive, with a consequent switch of strategy from reactive
in the searching phase to anticipatory breathing during prey-capture events. This study provides evidence that a generalist
diver may switch between different foraging strategies, and it shows how each of them may be optimal under particular ecological
conditions. These constraints influence the dynamics that operate within the marine food chains and have relevant implications
in managing lagoon areas, including fish ponds. |
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