The intensification and modernization of agriculture in the increasingly intensive agricultural landscape is one of the greatest threats to biodiversity in Europe and causes a continuous loss and degradation of natural habitats. This threat claims thousands of lives annually, especially of species that have become reliant on these areas for breeding, such as ground-breeding farmland birds. In addition, this causes a severe reduction in food resources for farmland birds. Among these threatened species is the endangered Montagu’s Harrier, which has experienced a sharp decline in several European countries, prompting extensive conservation measures. As a step towards saving the species, gaining insight in its diet is vital, as this factor strongly impacts their breeding success. Despite there is a lot of knowledge about their diet in vast parts of their breeding range, information about the prey preferences of SwedishMontagu’s Harrier’s is very limited. To determine which are the key prey species for the population, collection and analysis of pellets and prey remains were conducted during the 2023 breeding season on Öland, which is Sweden’s second-largest island and home to two-thirds of the nation’s Montagu’s Harriers. In total, 78 pellets and 38 prey remains containing 233 prey items were collected, and the results revealed that the population strongly relies on birds (76% of biomass consumed), while mammals were of less importance (22%). Insects and other prey items (≈1% each) contributed only minimally to the diet. The population thus stands out from other populations across Europe in its prey selection, indicating the need for increased and/or expanded protection of potential prey birds and their habitats, given that many bird species rely on a variety of habitats on the island. Further knowledge about the Montagu’s Harrier on Öland will be required to conserve the species as a part of the biodiversity it contributes to.