Distribution of grouse and their predators in peatland forest landscapes: A case for ecological integrity

Abstract

Natural peatland forest landscapes have been transformed and fragmented by forestry and agriculture worldwide, which undermines their ecological functioning and resilience. In Northern Europe, such transformations are apparently linked with observed long-term declines of forest dwelling grouse; those declines have not been effectively addressed by conservation. We asked how site factors, in combination with forest management and predation risk, shape grouse distributions in such landscapes in the breeding season. The data were collected by single-visit snapshot mapping of the capercaillie (Tetrao urogallus), black grouse (Lyrurus tetrix), hazel grouse (Tetrastes bonasia), and the signs of their potential predators across seven peatland forest areas (156 km2 in total) around large bogs in Estonia. We modelled the presence of grouse species in relation to landscape gradients, forest stand characteristics, and predator occurrence. The species were partly segregated along the bog-fen forest gradient (on different types of peat soils) and by stand composition; most capercaillie hens dispersed up to 2.5 km from lekking sites. All species avoided recently thinned forests, except breeding capercaillie in transitional mire sites (their preferred habitat). When the other factors were accounted for, the grouse neither avoided densely ditched areas nor predator vicinity at a forest scale (ca. 20-ha), which may expose the birds to unperceived risks. Our results indicate that conserving all three grouse species in peatland forest landscapes requires maintaining the edaphic and stand-structural diversity of the forests. Frequent thinning and dense predator populations are detrimental, and may require large refuge habitats to buffer their influence. Sustaining viable grouse populations serves as a clear target for ecosystem management in drained peatland landscapes.