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Midway’s Native Wildlife and the Threat Posed by Invasive Mice

Midway’s native plant and animal diversity have thrived for decades even in the face of human impacts, but now invasive mice are threatening the delicate balance.

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Mention of Midway Atoll brings to mind myriads of birds. But, there’s more to Midway.

Known as Pihemanu (“loud din of birds” in Hawaiian), Midway Atoll National Wildlife Refuge is a bustling (and noisy) spectacle of seabird life. Midway holds the title as the world’s largest albatross colony, with more than 1.5 million albatross packed on its three tiny islands including 73% of the world’s Laysan Albatross population and more than one-third of the global Black-footed Albatross population. For 9 months of the year, albatross dominate and manage to occupy every bit of inhabitable space. But, both above and below, birdlife abounds. Bonin Petrels and Wedge-tailed Shearwaters /ʻUaʻu Kani build extensive, maze-like burrows underground while Red-footed Boobies /‘A and Great Frigatebirds /‘Iwa nest overhead in trees and shrubs.

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Bonin Petrels (Pterodroma hypoleuca) nest in the sand on Midway Atoll. Credit: Rob Shallenberger

In addition to albatross, more than 20 other bird species use Midway for nesting, including two federally-listed species: the Critically Endangered Short-tailed Albatross and Laysan Duck. Currently surviving in only three populations in the Northwestern Hawaiian Islands, Laysan Ducks have been pushed to the point of extinction several times, but have miraculously survived and recovered thanks to critical efforts by scientists and conservationists. In 2004-2005, 42 ducks were translocated to Midway to serve as a back-up population. Since then, Midway’s Laysan Duck population has soared to several hundred.

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Since the translocation of 42 Laysan Ducks to Midway, the population has soared but invasive mice threaten this vital nesting habitat. Credit: Megan Dalton

Since 1986, when Midway was designated as a Refuge, the atoll entered a new era of restoration and revitalization. Now, the migrations and breeding cycles of birds, seals, turtles, and flowering sequence of the islands’ plant life define the seasons on Midway.

Although birds inhabited Midway for centuries in isolation, birds have (more recently) shared the atoll with humans. Along with humans came the accidental introduction of invasive rats and mice which threatened native seabird populations. In 1995, conservationists removed invasive rats and effectively protected Midway’s wildlife. That was, until 2015 when researchers discovered that invasive mice were attacking adult and juvenile albatross.

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Panoramic view of Eastern Island, covered with native plant species, namely Bunchgrass / ʻEmoloa / Kāwelu (Eragrostis variabilis), Alena (Boerhavia repens), and Nohu (Tribulus cistoides). Credit: Wieteke Holthuijzen

To only meet Midway’s wildlife would ignore an equally interesting and biodiverse segment of the onshore ecosystem, a unique assemblage of biota brought to the atoll by wind and waves (and later, people). More than 160 plant species occur on the atoll, but only two dozen or so are considered native, or at least indigenous to the Hawaiian archipelago. Among gently sloping dunes, one can spot these low-growing forbs and patches of dense grasses. Bunchgrass / ʻEmoloa / Kāwelu (Eragrostis variabilis), a robust grass endemic to the Hawaiian Islands, is now one of the most common native plants across the atoll landscape, often used as a “warrior species” for erosion control and dune stabilization. Other notable species include abundant and densely growing coastal shrub Naupaka (Scaevola taccada), which encircles the islands; Ilima (Sida fallax), which means “yellow” in Hawaiian, a low-growing plant with small bright golden flowers; and the perennial Sea Purslane / ʻĀkulikuli (Sesuvium portulacastrum), a pioneer species, growing on sunny, windy, sandy beaches, and coastal coralline areas.

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Laysan Duck surrounded by Pycreus Sedge (Cyperus polystachyos) and Sea Purslane / ʻĀkulikuli (Sesuvium portulacastrum). Credit: Megan Dalton

These species provide important ecosystem services (such as soil stabilization and flooding control), as well as important nesting and foraging habitat for a variety of wildlife. But not all plants are so helpful. Golden Crown-beard (Verbesina encelioides) was and continues to be Midway’s Most Wanted. A notorious invasive species, Golden Crown-beard once carpeted the islands with chest-high, impenetrable thickets. Through concerted control efforts by USFWS staff, volunteers, and contractors, Golden Crown-beard now only covers about 1% of the atoll—another step towards restoring Midway as a robust seabird island ecosystem.

Today, one of the leading threats to Midway’s plant and animal biodiversity is the presence of invasive mice. In 2015, predatory, invasive mice began to attack and even kill adult and juvenile Laysan Albatross, putting the global population at risk. The U.S. Fish and Wildlife Service, the Papahānaumokuākea Marine National Monument, Island Conservation, and other partners are going to remove invasive mice in July 2020. We have already secured 85% of the funds necessary to save Midway, but we need your help with the remaining 15%.

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About Wieteke Holthuijzen

Wieteke Holthuijzen is a National Science Foundation graduate fellow at Northern Illinois University, where she studies the ecological impacts of introduced house mice on Midway through a collaborative research effort with Island Conservation and the U.S. Fish and Wildlife Service. Previously, Wieteke served as the Invasive Plant Control Specialist on Midway, helping to restore the atoll to a bustling seabird colony. She is intrigued by the nexus of nature and human presence and seeks to study and contribute to the conservation of imperiled species. In her spare time, she enjoys playing the cello, ukulele, banjo, and electric bass.

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