We analysed trends in the breeding population of Great Cormorants in Greece during the period 1988–2014 when at least 20 colonies were recorded. The number of colonies doubled over the study period reaching 14 in 2014 from seven in 1988. There was also a continuous increase in the number of nests: from 952 in 1988 to 9256 in 2014, presenting an annual change of +26.5% ± 0.05 (SD). Most of the colonies were situated in freshwater lakes, three in deltas and one on the seacoast. Nine colonies were mixed with other colonially nesting species (mostly from the Ardeidae family). Of the 14 colonies 11 were found in trees. Two colonies were situated on the ground, four in bushes, two on reed rhizome islets and one on cliff ledges. Five out of the 14 active colonies in 2014, comprising 87% of the total recorded nests, were in wetlands of low altitude (0–45 m a.s.l.). The rest were situated in mountainous wetlands at altitudes ranging from 235 to 853 m a.s.l. One colony, at Lake Kerkini, contained the majority of nests in Greece (6650, being 72% in 2014). The second largest colony, at Lake Volvi, had 900 nests, followed by the Greek part of Prespa with 625 nests (in three colonies) in 2014. The percentage of nests in newly established colonies increased after 2003, reaching its highest value (14%) in 2009. The reason for the growth in both colonies and nests over the years is attributed to the increasing availability of fish, the protection status of wetlands and the absence of disturbance. Particularly after 2002 the species increased in numbers and established colonies in new areas, which is probably related to the expanding breeding populations of the species in north-eastern European countries and a corresponding increase in wintering numbers in Greece. This needs further attention by monitoring and research.
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Vol. 109 • No. 3