Changes in the diet composition of Pygmy Cormorant Phalacrocorax pygmeus on Skadar lake (Southern Montenegro)

Abstract

Changes in the diet composition of Pygmy Cormorant Phalacrocorax pygmeus on Skadar lake (Southern Montenegro) Diet changes of Pygmy Cormorant Phalacrocorax pygmeus, a piscivorous bird feeding primarily on fish up to 15 cm long, were studied on Skadar Lake. The breeding population on the lake was estimated at over 2,000 pairs in 2005 and 1,260 pairs in 2006, comprising about 5-8% of the regional population of SE Europe & Turkey. The first diet analysis, based on stomach contents of specimens hunted in the course of the breeding season, was carried out in the period 1973-1975 in order to identify the influence of the birds on commercial fishery. Further samples of regurgitated or accidentally dropped food items during the feeding of nestlings were collected and analyzed in the 2006 breeding season. Results from both periods are presented and changes in diet composition in the course of over 30 years are discussed. Between 1973-1975 and 2006, the Pygmy Cormorant's diet on Skadar Lake changed drastically. Only one fish species, Rudd Scardinius knezevici, was found to be common to both study periods. Pygmy Cormorant's diet in the period 1973-1975 consisted of 11 fish species (N = 224 specimens), belonging to five families. The most abundant fish species were Roach Rutilus ohridanus and Albanian Roach Pachychilon pictum. Diet analysis in 2006 revealed only six species (N = 98 specimens) from two families, and also showed that the introduced Goldfish Carassius auratus became a major food source for Pygmy Cormorant, constituting 84.7% of the total specimen number. Age class analysis of Goldfish items revealed that juvenile specimens (45-90 mm) comprised 89.0% of the total Goldfish compound. The study confirms that the Pygmy Cormorant is not a species-specific hunter and suggests it is not affected by the changes in composition of fish community in the littoral zone of the lake. Fish consumption by Pygmy Cormorants on Skadar Lake in 2006 was estimated at 45 t during the most intensive foraging period (June-August).