Biocenotic influence of the great cormorant (Phalacrocorax carbo L.) in the Azov-Black sea region of Ukraine

Abstract

The great cormorant (Phalacrocorax carbo L.) is a bird species that, due to the peculiarities of its biology, can significantly affect the natural environment. First of all, due to the fact that the species is an obligate ichthyophage and feeds exclusively on fish (causing, in some places, quite significant damage to both the fishery and the natural fish resources of the seas), a large amount of potassium, nitrogen and phosphorus compounds accumulates in its feces. Because of this, the caustic excrements of cormorants have a detrimental effect on herbaceous and woody vegetation in the colonies of this species, near them, as well as in the resting places of the birds. Considering the fact that the nesting colonies of the great cormorant can be quite numerous, reaching tens of thousands of nests (such as the settlement on the Obytichna spit in the Berdyansk district of the Zaporizhzhia region), the impact is observed to be very significant. At the same time, tree vegetation suffers from mechanical damage during the construction of nests, and trees die after 2-3 years. Another type of influence of cormorants is their interaction with other bird species in nesting areas. The high number of cormorants leads to a reduction in the number of some other bird species, the impoverishment of nesting bird complexes (herons, terns); in the conditions of a shortage of nesting sites on the islands, only (Larus cachinnans can nest together with the great cormorant (with its high number). We observed a similar situation in most nesting settlements of the species.