Trophic peculiarities of the Great Cormorant, Grey Heron and Long-tailed Duck on the Baltic Sea Lithuanian coast: a stable isotope approach

Abstract

The stable isotopes of nitrogen (δ15N) and carbon (δ13C) were analysed in the feathers of the Great Cormorant (Phalacrocorax carbo), Grey Heron (Ardea cinerea) and Long-tailed Duck (Clangula hyemalis) staying in the different seasons at the Lithuanian Baltic Sea coast. Stable isotope ratios in bird feathers represented dietary variations and foraging habitats during the feather growth period. Adult Great Cormorants fed juveniles by smaller fish at the beginning of fledging, switching later to larger prey. The stable isotope analysis indicated that the Grey Heron diet did not change significantly during the fledging period of their juveniles. The calculated trophic levels of Great Cormorants and Grey Herons were similar (3.55 ± 0.12 and 3.57 ± 0.41, respectively). The isotopic values in Grey Herons and Great Cormorants were 14.6–16.0‰ for δ15N and –27.3–(–24.9)‰ for δ13C. These values are typical of piscivorous bird species mostly feeding in freshwater bodies, i. e. in the Curonian Lagoon. The δ15N values found in the feathers of Long-tailed Ducks ranged from 7.7 to 13.9‰ and the δ13C values ranged from –33.6 to –24.9‰ showing high variation of feeding habitats during the moulting period: from freshwater to marine environment.