Great Cormorant (Phalacrocorax carbo) Science Article 3
Cormorants mainly eat fish, but remains of other prey are often found in their regurgitated pellets. Such remains are usually considered to stem from prey that were present in the stomachs of fish, eaten by the bird, i.e. from secondary prey. We present several cases were Great Cormorants Phalacrocorax carbo along the eastern North Sea actively took the polych te Nereis virens. This worm can grow to a considerable size (100 gram and almost 1 meter long) and swims freely in the water column during its spawning season in spring. We found large numbers of N. virens jaws in cormorant pellets in the breeding colony of Vlieland (Dutch Wadden Sea) and provide equations to backcalculate worm size and mass from jaw size. Other cases of cormorants eating N. virens were gleaned from the local white and grey literature. Some birds may have temporarily specialised on eating these worms, when they were available.
Leopold, M.F. & van Damme C.J.G. 2003, Marine Ornithology 31: 83-87