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Published: 2003-09-10 00:00:00

Magpies are not the ‘bad boys’ in attacking other bird species – pest animals do a lot more damage, this week’s Environment Waikato Biosecurity Committee heard.

The Council has been involved in a four year Landcare Research study to find out how magpies interact with native and other bird species. It found that, while they chase and kill other birds, they are far less of a threat than pest mammals.

The birds were studied in five regions – Waikato, Northland, Bay of Plenty, Wellington and Southland. Each region established two blocks, one where magpies were killed and one where they were left. At the end of the study, magpie populations in kill blocks had dropped by 60 to 80 percent, and kereru populations had increased by 130 percent, with variable results for tui.

But Landcare pest ecologist John Innes said more sightings did not mean more birds, and magpies seemed to control how often the birds were seen, rather than numbers. When territorial magpie pairs were removed the area was re-invaded by non-territorial flocks, creating an endless and expensive battle to control them.

Magpies chased and occasionally killed other birds to keep them away from food sources, but councils should not invest large amounts in large-scale magpie control. It was better to concentrate on controlling mammal pests, which attacked nests and limited native bird numbers.

Magpies were conspicuous, noisy and active during the day, while ship rats, possums, cats and stoats were secretive, silent, tree dwelling and moved around at night.

Magpies did attack other birds, killing two thirds of small birds but only a small number of larger birds. They attacked all year round but only killed in the breeding season, when they also attacked people.

He said controlling magpies would increase access to food resources for other birds, but councils should not undertake large scale magpie control to increase numbers of other birds, as native birds were more likely to be limited by mammal predators. Removing cats could also be a mistake in some areas, as they controlled ship rats, which were the main predator of birds’ eggs.