Postnatal growth of the great cormorant Phalacrocorax carbo sinensis (Aves: Phalacrocoracidae) in northeastern Mediterranean wetlands

Postnatal growth of nestling great cormorants Phalacrocorax carbo sinensis was studied at two northeastern Mediterranean wetlands, the Lakes Kerkini and Mikri Prespa, northern Greece. A method for constructing growth curves from only two visits to bird colonies was used. Logistic growth parameters re-calculated from the logarithmic equation fitted well to the actual growth data of initial-final measurements of body mass, bill length, bill + head length, and tarsus length. Growth rates (K) did not significantly differ between colonies for all variables: body mass (0.205 and 0.206 day(-1) at Lakes Kerkini and Mikri Prespa respectively), bill length (0.131 and 0.147 day(-1)), bill + head length (0.109 and 0.121 day(-1)) and tarsus length (0.201 and 0.215 day(-1)). Asymptotic values (A) did not significantly differ between colonies for body mass (2126.7 g and 2128.95 g) and bill length (70.57 and 68.83 mm) but did so for bill + head (147.89 and 151.51 mm) and tarsus length (75.42 and 71.31 mm). The inflection point (T) was similar for body mass (16.6 and 16.4 days) and tarsus length (7.9 and 7.1 days) but significantly different for bill (13 and 11.2 days) and bill + head length (12.2 and 11.1 days). Climatic conditions and food availability were not considered as factors greatly affecting the observed intercolony variation, and therefore other proximate and ultimate factors should be further examined. The proposed method is very helpful because growth curves can be constructed with the allocation of the smallest amount of time and effort, while at the same time keeping the disturbance of vulnerable breeding avian populations to the minimum level. Furthermore, and provided that other factors are controlled, this method could be used for the monitoring of the influence of spatial and temporal variation of ecological conditions on nestling growth.