Some 50 feral cats are running around the Schiermonnikoog National Park, a recent study by the University of Groningen shows. These feral cats mainly live on field mice, rabbits, hares and birds. The cat population does not appear to have increased on the Dutch is very much since the cull in the early 1990s ended.Feral cats are not dependent on humans. They live ‘in the wild’, where they scavenge for their food and rear their litters of young.
Feral cats are often larger than domestic cats and their behaviour also differs; they are generally more wary and sometimes quite aggressive. The feral cats on Schiermonnikoog are descendants of domestic cats in the village of the island, from which they once escaped, or they were abandoned. There has been a permanent population on the island for several decades.
Cats can have a considerable impact on local fauna. Dozens of species have become extinct as a result of the introduction of the cat! This has happened mainly on islands which previously had no predators. On Schiermonnikoog too there is no natural main predator, and ground and hole nesters are at risk as a result, as is the rabbit, for example, whose population has not yet fully recovered from the effects of the VHS virus.
Last summer, MSc student Tjitse op de Hoek placed camera traps on the east and west sides of the island. These took photos of passing animals. In this way the presence of individual cats could be recorded and their numbers ascertained. In addition, he sifted through 180 sets of cat faeces to establish what the animals eat.
The study revealed that the feral cats mainly eat field mice. The field mouse has only been on the island since 1996, arriving with a cargo of hay shipped from the mainland. Rabbits, hares and birds also appear to form a large part of the diet. The University would like to repeat the study in the spring to see if the feral cats’ diet switches from mammals to birds during the nesting season.
This study is a first step towards establishing the impact of feral cats on the island. On the basis of this initial population survey and the follow up to the diet study, the impact on prey populations and, subsequently, on the entire ecosystem will be determined.
Dr Chris Smit, Community and Conservation Ecology Department of the Center for Ecological and Evolutionary Studies (CEES), University of Groningen, c.smit rug.nl, tel. 050-363 8833.
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