House Mouse: The animals are opportunists and omnivores
Photo: Michael Dietrich / imagebroker / IMAGO
Mice don't have the best reputations, especially when they're in large numbers.
Mice are invasive on many islands.
The rodents benefit from their character: mice are opportunists and omnivores.
Researchers from Louisiana State University have found that invasive house mice on Southeast Farallon Island south of California are having a major impact on the native ecosystem.
The study was published in »PeerJ—Life and Environment«, reported by the magazine Spektrum.
Located about 50 kilometers west of San Francisco, Southeast Farallon Island is the largest of the islands that make up the Farallon Islands National Wildlife Refuge -- the largest seabird breeding colony in the United States, the authors write.
The mice would not be native to the island and would probably have inadvertently arrived in the 19th or 20th century.
After all, they formed one of the world's highest densities of mice on an island: according to a report, around 50,000 house mice live on an area the size of around two football pitches.
A team led by Michael Polito, professor of oceanography and coastal sciences, studied the ecological niche of invasive house mice on the island to understand feeding habits in relation to regional flora and fauna, the study says.
"Prior to this study, there was no data on what exactly mice eat on the island and how their diet changes over the year," Polito is quoted as saying in the statement.
To study the mice's diet, the researchers used a technique that allows them to detect food sources in the mice's tissues.
In addition, the team studied the seasonal abundance of the mice over a 17-year period and related them to the availability of native seabirds, salamanders,
The result: Mice are opportunistic omnivores.
The population numbers and eating habits fluctuate with the seasons, which is how the rodents react to a changed food supply, the authors write.
In spring, when the population is low, the mice feed mainly on plants.
In summer, however, when the population increases, especially of insects and seabirds - finally in autumn, at the peak of the population, they eat almost exclusively insects.
This would put the mice in competition with the Farallon tree salamander: a species found only on the island.
The population declines again in the winter months.
It is unclear whether the mice hunt seabirds directly or eat abandoned eggs or carcasses.
However, previous studies have found that the mere presence of mice on the islands attracts predators such as owls, which in turn can attack the resident seabirds.
The fact that it is an island also increases the influence of the mice: "Native plants and many animals cannot leave the island to flee from the mice," Polito is quoted as saying.
"These plants and animals have never had to develop defensive behaviors against rodents like the mainland species have developed."
The researchers conclude that the mice, due to their large numbers and opportunistic diet, have far-reaching effects on the island's ecosystem - and that their eradication should therefore be considered.
"Our study provides the latest and most comprehensive insights into the diets of mice and the effects they have on the native community - particularly the endemic tree salamander," said co-author Pete Warzybok.
"These results support more than ever the eradication of mice as a critical step in restoring the ecosystem of the Farallon Islands."
It is particularly important to monitor after eradication,