Non-native REd-Billed Blue Magpie Urocissa erythrorhyncha Expanded Into Lowland Areas with Moderate Forest Cover, with No Significant Impact on Native Common Bird Occupancy, in Shikoku, Southern Japan

Non-native bird species have colonized and negatively affected natural ecosystems and social economics globally; however, most cases have been poorly studied. We evaluated the effectiveness of playback surveys for enhancing detectability of the non-native Red-billed Blue Magpie Urocissa erythrorhyncha, and revealed the drivers of the magpie's distribution using an occupancy model that considers the detection process and effects of survey conditions in Shikoku, southern Japan. Using this model, we mapped the potential distribution of suitable magpie habitats across Shikoku. Furthermore, we obtained detection/non-detection data for native bird species (Narcissus Flycatcher Ficedula narcissina, Varied Tit Poecile varius, Japanese Tit Parus minor, and Japanese Bush Warbler Cettia diphone), and evaluated the impacts of magpie presence on occupancy of these native bird species using a multispecies occupancy model that considered interspecific interactions (i.e., co-occurrence or mutually exclusive occurrence patterns). The results showed that detection probability was enhanced by broadcasting a specific series of magpie calls in the early morning from late May to early July. Magpie occupancy was higher in areas of lower elevation and peaked in areas with moderate forest cover (76%). However, magpie presence did not significantly affect the occupancy of four native bird species. Mapping the distribution of magpie occupancy demonstrated that potentially suitable habitats are widely distributed in near-coast areas between lowlands and mountains, even in eastern Shikoku, which has not yet been colonized. Therefore, before the magpie expands across Shikoku and becomes prevalent, it will be necessary to further assess potential impacts of magpies on local native species, develop efficient methods to capture magpies, and establish a monitoring scheme in priority areas to block magpie expansion. Our approach, using a combination of playback surveys and models considering detectability, holds potential for application in studies of other non-native bird species, as well as to support their appropriate management.