DEVELOPMENTAL RATES AND MORPHOMETRICS OF THE SYMPATRIC PYGMY CORMORANT (PHALACROCORAX PYGMEUS) AND GREAT CORMORANT (P. CARBO SINENSIS)

Abstract

We compared growth rates and adult morphological traits in two sympatric cormorant species, the pygmy cormorant (Phalacrocorax pygmeus) and the great cormorant (P. carbo sinensis), in Israel. The smaller P. pygmeus exhibited higher developmental rates than P. carbo sinensis, as expressed in the growth rate constant (K) of body mass and of various body parts (bill, wing, tarsus, primaries, and tibia lengths). The consequences of the higher developmental rate of P. pygmeus are early fledging and a relatively low body mass of fledglings. We suggest that several proximate ecological and developmental factors such as risk of nest predation, body temperature regulation, and hydrodynamics act in concert to promote rapid development in chicks of P. pygmeus. However, the four-fold lower body mass of the adult P. pygmeus is probably the most important physiological constraint that might explain its rapid growth rate in comparison with P. carbo sinensis. The body mass and the size of various body parts of adult P. carbo sinensis are much higher than those of adult P. pygmeus. This difference in adult morphological attributes, together with the marked differences in growth rates between the two species, should be reflected in different ecological functions that promote ecological segregation between them. Therefore, the conservation policies and future practical solutions of the cormorant-fisheries conflict should be species-specific.