This zapovednik protects a belt of 184 square miles (476 km2) of pristine boreal forest along the border shared by Russia and Finland, with an abundance of wildlife species including reindeer, wolves, brown bears, lynx, wolverines, and golden eagles.
Beaver colonies are on and around most of the 250 lakes and rivers, as are mink and occasionally river otters. Black-throated loons, whooper swans, and bean geese nest on shores and islands and sometimes on beaver dwellings.
Capercaillies and black grouse dance in springtime display for mates in forest clearings alive with songs of small passerines—chaffinches, bramblings, rustic buntings, chiffchaffs, and redstarts. More than 650 species of butterflies and moths sip nectar from flowers of bog bilberries, cowberries, cranberries and cloudberries which later produce bountiful harvests for bears and many birds.
Great gray owls swoop down by day as well as night for voles and lemmings. More than 100 of the 130 bird species nest, including white-tailed sea eagles, ospreys, and peregrine falcons. Long-tailed ducks are abundant in migration and goldeneyes, mallards and teals all summer.
Many are gone by October’s first snowfall but some small birds can make it when snowpack is a yard (meter) thick with temperatures of -35°F (-40°C)—among them two-barred, parrot, and common crossbills, diminutive kinglets, and Eurasian dippers which continue to sing and do their thing around (and in) unfrozen rapids of the Kammenaya River.
Kostomukshsky is part of a green belt which in 1990 joined with reserves on the Finnish side of the border to form a trans-boundary area for cooperative conservation and sustainable nature use, a proposed U.N. World Heritage Site. Unfortunately, barbed wire fence now along the border impedes animals’ west–east movements and poaching has almost halved reindeer numbers, also moose, and with them, wolves. Other problems include logging on adjacent lands and pollution from the Kostomukshsky iron ore factory.