Prey ecology and behaviour affect foraging strategies in the Great Cormorant

The Wne link between a particular dive pattern and a speciWc prey item represents a challenging task in the analysis of marine predator–prey relationships. There is growing evidence that prey type aVects diving seabirds’ foraging strategies, dive shapes and underwater activity costs. This study investigates whether a generalist diver, the Great Cormorant Phalacrocorax carbo, modiWes 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 Xesus, aVect 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 Wsh species increases prey-capture rates. Conversely, Mullets exploit the whole water column and are highly mobile, and this is reXected 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 diVerent foraging strategies, and it shows how each of them may be optimal under particular ecological conditions. These constraints inXuence the dynamics that operate within the marine food chains and have relevant implications in managing lagoon areas, including Wsh ponds.