Rising from the Pacific Ocean about 30 miles off the California coast, the Farallon Islands are home to some unique species of flora and fauna and breeding grounds for countless seabirds. But since the 19th or early 20th century, domestic mice have also been introduced here, and their hunger is becoming an increasing problem for the rest of the population. As noted and described by Michael Poleto of Louisiana State University and his team in PeerJ-Life and Environment.
In the southeast of Farallon Island, the working group analyzed how the feeding habits of the rodents change throughout the year and what the consequences are for the environment there. The island is only a few hectares in size and is sometimes home to as many as 50,000 mice. The researchers picked up some of them and analyzed their diet with the help of isotope analysis: depending on the food consumed, it leaves a typical isotopic imprint in the body.
It is not surprising that animals eat everything that comes their way, but the composition changes throughout the year. In the spring, when rat numbers are still low, they prefer plant food. But as soon as they multiply and increase in number, they more and more often turn to animal food: in the summer they further enrich their diet with insects and seabirds. Finally, in the fall, the number of mice reaches a maximum; Now they eat insects almost exclusively. Finally, in winter, the numbers of rodents decrease again and they resort to a mixed diet that includes plant seeds, among other things.
Thus, rodents affect the environment in different ways: the loss of plants and seeds hinders the renewal of vegetation. Their appetite for insects puts them in direct competition with the Farallon salamander, which lives only on the islands of this archipelago and is threatened by introduced mice. However, it is unclear whether the rodents hunted seabirds directly, ate “only” their eggs or chicks, or used them as carrion. The rats introduced to the Atlantic Gough Island have learned to hunt even large birds such as albatrosses and eat them almost alive. However, their mere presence in the southeast of Farallon Island has attracted non-native predators there, such as owls, which now also hunt seabirds.
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