Martens in the Apostle Islands National Lakeshore Annual report (11/1/2018 – 5/1/2019)

Welsch, Britta; Farmer, Morgan; Mallinger, Elyse; Shen, Yunyi; Gottwig, Lindsey; Morrison, Megan; Olson, Erik; Van Deelen, Timothy; Van Stappen, Julie

American martens (Martes americana) occupy a complex niche space in the Great Lakes region mammal communities, and are potentially subject to top-down effects, bottom-up effects, and intraguild competition. This dynamic is complicated in island systems because the island biogeography itself may structure mammal communities. Managers need to understand these competing dynamics in order to conserve the full diversity of mammals. Currently, American martens are among the only state-endangered mammals in the state of Wisconsin and are known to inhabit eight of the islands of the Apostle Islands archipelago within the Apostle Islands National Lakeshore. This report details progress on two broad efforts to understand potential drivers of marten presence in the Apostle Islands – intraguild interactions and prey availability. During 11/1/2018 – 5/1/2019, we deployed 113 cameras on 11 islands and the mainland that recorded approximately 157,000 images. Data obtained through November 2018 suggests that carnivore communities are shaped primarily by island biogeography, with island size and distance from mainland as primary drivers. Additionally, mesocarnivore species rely heavily on small mammals for prey resources. To better understand how small mammal prey communities may be impacting the marten population within the archipelago, we inventoried small mammal communities using small mammal trapping techniques on twenty of the twenty-one islands and a portion of the mainland in the summers of 2017, 2018, and 2019. We compared the results of our surveys with the results of historical small mammal surveys going back to 1961 to gain a better understanding of small mammal community dynamics in the archipelago. Small mammal communities changed over time, likely as a result of vegetative succession, interspecies succession, and biogeographical forces influencing island-level extinction and colonization events. Red-backed voles, a preferred prey of marten in Wisconsin, had historically stable abundance and distribution. Additional trapping of small mammals will be required to further develop an understanding of small mammal community structure, dynamics, and their influence on martens.