Diving costs and benefits during post-breeding movements of the Mediterranean shag in the North Adriatic Sea |
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Authors: | Stefano Sponza Barbara Cimador Mauro Cosolo Enrico A Ferrero |
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Institution: | (1) Department of Life Sciences, University of Trieste, via Giorgieri 9, 34127 Trieste, Italy |
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Abstract: | From the 1980s, Mediterranean shags Phalacrocorax aristotelis desmarestii have become regular summer visitors in the Gulf of Trieste (N-E Italy), as post-breeding movements from Croatian breeding
colonies. To characterize such a recent habit and to explore diving optimality models, we investigate foraging strategies
and diving patterns at different depths, during breeding and post-breeding seasons. Behavioural data were cross-checked with
the species’ diet. Shags foraged on and close to the sea bed, with a prevalent anticipatory breathing strategy. In the Gulf
of Trieste, the shallow depths and low mobility of prey allowed shags to use just the oxygen of the respiratory tract, reducing
the physiological stress for diving. In Croatia, dive costs increased with depth and prey mobility, resulting in a higher
oxygen expenditure that involved also respiratory stores. Such ecological and physiological aspects characterize the Gulf
of Trieste as an optimal area for feeding and restoring from the costs of breeding season incurred in Croatia and could be
the basis of these post-breeding movements. |
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Keywords: | |
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