Sand Island, part of a small atoll in the Northwestern Hawaiian Islands, is home to a diverse range of bird species, including most notably hundreds of thousands of mōlī (Laysan Albatross). However, these birds face a significant threat from introduced invasive rodents, which attack nesting mōlī. A recent study, published in the influential journal Public Library of Science One (PLOS ONE), sheds light on the intricate challenges of conservation on the island, which is part of Midway Atoll National Wildlife Refuge (NWR).

PhD candidate Wieteke Holthuijzen of the University of Tennessee, Knoxville, is the lead author of the study, titled “An invasive appetite: combining molecular and stable isotope analyses to reveal the diet of introduced house mice (Mus musculus) on a small, subtropical island.” The research aimed to investigate the role of invasive rodents on Sand Island by studying their diet and predicting the potential consequences of their removal.

What sets this study apart is its unique methodology. The scientists utilized next-generation sequencing, a cutting-edge analysis that examines DNA to identify the species consumed by the invasive mice. Additionally, stable isotope analysis was employed to measure the proportions of different types of food in mouse diet. This combination of methods allowed for a comprehensive understanding of how invasive mice influence the island’s ecosystem.

Holthuijzen emphasizes the importance of understanding the interactions between invasive species and ecosystems, stating, “More eradications are being planned on larger, increasingly complex islands—but, we need more research to predict and prepare for how these kinds of ecosystems will respond to rodent removal. Given Sand Island’s history of human activities and landscape modification, it represents a unique case study of how mice influence islands with highly-altered ecosystems.” The findings of the study revealed that the invasive mice not only prey on mōlī but also consume many non-native arthropods and invasive plants.

Jonathan Plissner, a study co-author from the US Fish and Wildlife Service, said: “Identifying population-specific rodent diets can help develop the most effective bait formulations, help determine most effective timing of removal efforts, and determine if measures can be taken to limit availability of alternative food sources.”

To ensure successful conservation outcomes, the study emphasizes the necessity of robust management efforts before and after rodent removal, particularly for highly-managed or disturbed islands. Holthuijzen stresses the significance of mitigating “surprise effects” or adverse outcomes through pre- and post-eradication management efforts.

Coral Wolf, a co-author on the study and conservation impact manager at Island Conservation, said, “Removing invasive species that prey on seabirds, such as the invasive rodents on Sand Island, is crucial for restoring healthy seabird populations and the associated land-sea nutrient flows.”

The study highlights that diet analysis should be used as a preliminary measure before rodent removal; this is a key step to understanding how rodents affect the broader ecosystem and determine which species are most likely to respond and recover. The study also calls for strong partnerships with organizations and communities that possess valuable local knowledge to implement place-based management approaches. The U.S. Fish and Wildlife Service, who manage Midway Atoll NWR, were key partners in the work and model the kind of collaboration that would spell success for removal endeavors.

Beth Flint, co-author from the US Fish and Wildlife Service, said, “It is hard to overestimate the profound effect of introduced rodents on insular ecosystems.  This study has broken new ground in helping understand the details of the role house mice play in the anthropogenically modified system at Midway.”

This study serves as a reminder that conservation is a complex endeavor, requiring a comprehensive understanding of the interactions between species and ecosystems. By using a collaborative, evidence-based approach, we can work towards restoring whole ecosystems and reaping the multiple benefits of invasive species removal on islands.