Researchers identify dietary impacts of invasive mice on the Farallon Islands

View of South East Farallon Island from West End. Credit: Point Blue Conservation Science

On an island 30 miles off the coast of San Francisco, a horde of invasive house mice packs a bigger ecological punch than their small sizes suggest. Those are the findings of a study led by Michael Polito, associate professor of oceanography and coastal science at LSU, along with researchers from Point Blue Conservation Science, San Jose State University, and California State University Channel Islands. . The study was published today in PeerJ—Life and environment.


The island in question is Southeast Farallon Island, part of the Farallon Islands National Wildlife Refuge, home to the largest seabird breeding colony in the contiguous United States and many unique native species. of plants and animals. House mice are not native to the island but were introduced unintentionally during the 1800s or early 1900s. Since then the population of has grown to around 50,000 house mice inhabiting the island at approximately the size of two football fields. The study found that the mice consume and/or compete for food with native species and therefore support the US Fish and Wildlife Service’s proposed plan to eradicate the mice from all of the South Farallon Islands.

The research team identified the impact of mice on this island ecosystem by first gaining a better understanding of mouse abundance and diet.

“Prior to this research, there was a lack of data on what exactly mice ate on the island and how their diets changed throughout the year,” Polito said.

House mice were unwittingly introduced to the Farallon Islands National Wildlife Refuge, home to the largest seabird breeding colony in the contiguous United States, and the population swelled to approximately 50,000 house mice inhabiting the island shortly. nearly the size of two football fields. The study found that the mice consume and/or compete for food with native species and therefore support the US Fish and Wildlife Service’s proposed plan to eradicate the mice from all of the South Farallon Islands. Credit: Point Blue Conservation Science

To study the mice’s diets, the scientists used a technique called stable isotope analysis, which traces the unique chemical signatures of food sources in the mice’s tissues.

“Effectively, mice are what they eat,” Polito said.

Additionally, Polito and his colleagues examined the seasonal abundance of introduced mice over a 17-year period and linked it to the availability of native seabirds, salamanders, insects, and vegetation on the island.

Small rodent, big appetite

House mice were unwittingly introduced to the Farallon Islands National Wildlife Refuge, home to the largest seabird breeding colony in the contiguous United States, and the population swelled to approximately 50,000 house mice inhabiting the island shortly. nearly the size of two football fields. Credit: Point Blue Conservation Science

They conclude that mice are highly “omnivorous and opportunistic” feeders whose population numbers and diets vary greatly throughout the year in response to changes in food availability and seasonal climate. The researchers found that in the spring, when the mouse population is low, they mainly eat plants. As summer arrives, when their numbers begin to increase, the mice begin to feed more on native insects and seabirds. In the fall, when the mouse population is booming, their diet shifts more to insects, putting them in direct competition with the Farallon tree salamander, a species found only on the islands. The number of mice then declines during the cooler, wetter conditions of winter.

Small rodent, big appetite

This study found that the mice consume and/or compete for food with native species such as the endemic Farallon Salamander and therefore supports the US Fish and Wildlife Service’s proposed plan to eradicate the mice from all Farallon Islands. from South. Credit: Point Blue Conservation Science

Although it is still unclear to what extent mice actively prey on seabirds or simply scavenge abandoned eggs and carcasses, previous studies have shown that the mere presence of mice on islands attracts migratory predators, such as than burrowing owls, which then feed on rare species. native seabirds. The very nature of the island environment itself also leads to invasive mice having an outsized impact.

“Native plants and many animals cannot leave the island to get away from mice, and these plants and fauna have never had to develop defensive behaviors against rodents like mainland species,” said Polito.

Small rodent, big appetite

This study’s analysis of the ecosystem of the Farallon Islands, the largest seabird breeding colony in the contiguous United States, was conducted at Louisiana State University. Credit: Point Blue Conservation Science

The researchers conclude that the mice have broad influences on the island’s ecosystem due to their high abundance and opportunistic diet.

“Our study provides the latest and most comprehensive understanding of mouse diet and its impacts on the native community, particularly the endemic tree salamander,” said Pete Warzybok, Farallon Islands Program Manager at Point Blue. Conservation Science and a co-author of the article. “These findings make the case for mouse eradication more than ever as a critical step in restoring the Farallon Islands ecosystem.”


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More information:
Michael J. Polito et al, Population dynamics and resource availability drive seasonal changes in consumption and competitive impacts of introduced house mice (Mus musculus) on an island ecosystem, PeerJ (2022). DOI: 10.7717/peerj.13904

Journal information:
PeerJ

Provided by Louisiana State University

Quote: Small Rodent, Big Appetite: Researchers Identify Dietary Impacts of Invasive Mice on the Farallon Islands (2022, September 22) Retrieved September 22, 2022 from https://phys.org/news/2022-09-rodent-big- appetite-food-impacts.html

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