Development of the Rybinsk Reservoir by the Great Cormorant Phalacrocorax carbo in Russia, 1941– 2024

The Great Cormorant Phalacrocorax carbo is a long-lived, range-expanding fish-eating predator.Many populations across the species' extensive range today are show increased in abundance.This study provides new knowledge about the Great Cormorant colonizing the Rybinsk Reservoir, the northernmost of the cascade of reservoirs of Europe's largest river, the Volga, in the East European (Russian) Plain.The aim of the work is to study the historical and current distribution of the species in the Rybinsk Reservoir, estimate its abundance and identify the breeding status in the study area.The basis of the work is information from the beginning of the formation of the Rybinsk Reservoir in 1941 until 2024.Great Cormorants have visited the reservoir at varying intervals since 1946.Recordings of cormorants were sporadic and irregular until 2015, after which the birds began to be observed annually at the reservoir.In the fairway zone of the Rybinsk Reservoir in 2020 and 2021, the abundance of Great Cormorants and the share in the bird population (%) varied from 0.10 (3.22%) to 0.31 (6.34%) individuals/km, respectively.The current expert number of Great Cormorants seasonally inhabiting the reservoir is estimated at 100-150 adult and immature individuals.The Great Cormorant began nesting on the Rybinsk Reservoir for the first time in 2017.Both in the past and at present, cormorants migrate to wintering places, do not winter in the reservoir, and do not form sedentary populations.