Sexual differences in the diet of great cormorants Phalacrocorax carbo sinensis wintering in Greece

Abstract

Sexual differences in the diet of the great cormorant, Phalacrocorax carbo sinensis, were studied in four Greek wintering areas, the Amvrakikos Gulf, the Axios and Evros Deltas and the Messolonghi Lagoon, through the analysis of stomach contents. Great cormorants are birds sexually dimorphic in size, with males being generally larger than females. Although similar prey species were found in the stomachs of both sexes in all the studied areas, significant differences were observed with respect to the proportion of species taken. Male birds ate higher proportions of large fish species such as grey mullets, European sea bass, Dicentrarchus labrax, and Prussian carp, Carassius gibelio, while female birds took higher proportions of smaller species such as big-scale sand smelt, Atherina boyeri, and black goby, Gobius niger. As a consequence, male great cormorants were found to feed on significantly larger prey than did females by means of fish standard length and body mass. There was no significant difference between the sexes in the mass of food found in stomachs.

Trophic Transfer of Trace Elements in an Isotopically Constructed Food Chain From a Semi-enclosed Marine Coastal Area (Stagnone di Marsala, Sicily, Mediterranean)

“…L. michaellis belonged to similar trophic levels but exploited less enriched sources. Finally, P. carbo was at the top of the food chain, reaching d 15 N values of 18%, compatible with the exploitation of nonsampled large carnivores, whereas the role of mugilids and sea bass as prey seems to be less important here than in other coastal areas (Barati 2009;Liordos and Goutner 2009). …”

Intersexual differences in the diving behaviour of Imperial Cormorants

“…We suggest that this apparently inconsistent result can be explained by differences in the swim speed associated with the different hunting strategies used by both sexes. There are intersexual differences in the diet of similar cormorant species (Favero et al 1998;Casaux et al 2001;Liordos and Goutner 2009;Quillfeldt et al 2011), with females preying on smaller specimens than males. Unpublished data also suggest that this is also the case for foraging Imperial Cormorants from Punta León.…”

Otolith retrieval from faeces and reconstruction of prey-fish size for Great Cormorant (Phalacrocorax carbo) wintering at the East Dongting Lake National Nature Reserve, China

“…Otoliths of fish are species-specific in morphology and shape, and have been used in prey fish identification for stomach-content analysis of piscivorous fishes (Blackwell and Sinclair 1995;Labeelund et al 1996) and also for regurgitated food remains of piscivorous birds (Veldkamp 1995;Kubetzki and Garthe 2003;Liordos and Goutner 2009). Being dense and able to withstand some degree of dissolution when compared to other hard structures of the fish, otoliths can remain in the faeces of piscivorous birds for relatively long time periods; thus prey can be identified based on species-specific characteristics of otoliths, and preyfish size can be estimated using calculated relationships between otolith size and fish size.…”