Great Cormorant (Phalacrocorax carbo) Science Article 14
The perch fidelity of the Cormorant Phalacrocorax carbo sinensis has been studied during migration and winter time on a roost at Lake Geneva, Switzerland. A one-perch fidelity index was computed for 217 individuals. It appears that the perch fidelity increases with the age of the Cormorant, but is not correlated with the duration of stay of the bird on the roost. This last point, confirmed by examples of young birds migrating to the south and showing a high fidelity during their short stay on the roost, tends to prove that the competition for a perch on inland lakes is but one of the factors influencing the latitudinal distribution of the Cormorants according to age.
Reymond A. & Zuchuat O, ARDEA 83 (1): 281-284.