Abstract

The Oriental Magpie Pica serica invaded Hokkaido, Japan, in the 1980s, but little is known about its current population status or potential for further range expansion. Here, we compile records on the distribution of magpies from 2012 to 2016 and estimate potential suitable habitats. Field surveys and citizen science reports revealed that breeding and individual birds occurred in 28 municipalities located in western Hokkaido. Although dozens or more birds have become established in three of these municipalities on the Pacific coast, populations in the other 25 appear not self-sustaining. Suitable habitats for magpies were almost exclusively limited to urban residential areas, presumably due to the availability of anthropogenic food resources. While these apparently suitable habitats occur throughout Hokkaido Island, no sightings have been recorded in eastern Hokkaido, suggesting that magpies have not crossed the forest area that runs north–south through the central part of the island. Suitable habitats, estimated based on the habitat selection by the largest population in Tomakomai, are concentrated near the centers of each municipality, separated by agricultural land, which may have slowed down the range expansion of the magpie through the Allee effect. The island-like fragmentation of suitable habitats is advantageous for comparative studies of magpie populations, food resources, predators, and competitors. Furthermore, the magpie has a distinctive black-and-white coloration and a unique, loud call, making it well-suited for citizen science surveys. Continuous monitoring of Hokkaido’s magpie population by experts and citizens will provide excellent opportunities to ask ecological questions involving bird distributions and the establishment of invasive species.

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