Cats even worse for birds than previously documented18/04/2013 08:46:31 Study documents dramatic new impacts to birds from outdoor cats
April 2013. A study by British scientists has documented for the first time significant new impacts to birds from outdoor cats, reporting that even brief appearances of cats near avian nest sites leads to at least a doubling in lethal nest predation of eggs and young birds by third-party animals, as well as behavioural changes in parent birds that lead to an approximately 33 percent reduction in the amount of food brought to nestlings following a predation threat.
The study, which was led by Karl Evans of the University of Sheffield, was carried out by observing 47 blackbird nests in 2010 and 49 nests in 2011 in Sheffield, during the breeding season from March to August and comparing nest dynamics following presentation of a taxidermist-prepared cat, a predatory grey squirrel, and a rabbit. The crucial finding is that the natural response of parenting birds to the appearance of predators - alarm calling and nest defence - dramatically affects rates of bird nest predation by third-party animals having been alerted to the nest, as well as much lower feeding rates of young birds for prolonged periods following the threat of predation by cats.
Cats prompted most alarm & predation
"Reduced food delivery, even over short time periods, can adversely influence chick condition and reproductive success and over longer time periods can promote smaller clutches," the study said.
The study said that the behavioural changes in birds caused by the appearance of cats "....may have considerable implications for (bird) population and community dynamics" and suggests that "...the impacts of sub lethal effects on avian prey populations are frequently greater than those arising from lethal effects....."
The study concludes that whilst cats housed indoors require more care and attention from their owners the most effective management option is thus to house cats permanently indoors. About half of cat owners in North America do this to prevent cats having road traffic accidents or being injured in fights with other cats.
Serious impact of cats on bird populations
Cats kill up to 20 billion animals in US every year
That study's estimate of bird mortality far exceeds any previously estimated U.S. figure for cats. In fact, this magnitude of mortality may exceed all other direct sources of anthropogenic bird and mammal mortality combined. Other bird mortality sources include collisions with windows, buildings, communication towers, and vehicles, as well as pesticide poisoning.
The study estimated that the median number of birds killed by cats annually is 2.4 billion and the median number of mammals killed is 12.3 billion. About 69 percent of the bird mortality from cat predation and 89 percent of the mammal mortality was from un-owned, or feral, cats.
The study was peer-reviewed and published in the Journal of Applied Ecology (January 30, 2013). The study was led by Karl Evans of the Department of Animal and Plant Sciences, University of Sheffield in collaboration with his PhD student Colin Bonnington and Kevin Gaston of the Environment and Sustainability Institute, University of Exeter.
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