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Alien bird species mapped

The mallard duck – shown here on Lake Wanaka – was introduced to New Zealand from England between 1870 and 1930 The mallard duck – shown here on Lake Wanaka – was introduced to New Zealand from England between 1870 and 1930 skyearth
12 Jan
New Zealand, Australia, and other former British colonies among the world’s hotspots for alien bird species richness

‘On the whole, the results of acclimatisation in New Zealand must be considered favourable,’ wrote naturalist and geologist Frederick Wollaston Hutton in his 1904 book The Animals of New Zealand: An Account of the Dominion’s Air-Breathing Vertebrates, ‘although unfortunate mistakes have been made’.

These ‘unfortunate mistakes’ to the act of ‘acclimatisation’ – deliberately introducing wildlife from Britain into the far-flung colonies of the British Empire, such as Australia, New Zealand, and South Africa, in order to enable pastoral farming, hunting, or to simply make these foreign lands feel more like the comforts of home – are, in Hutton’s view, primarily restricted to the release of rabbits, as well as small carnivores such as weasels, ferrets, and stoats. However, a great many different species were introduced, everything from deer to pigeons, salmon to doves, sheep to lobsters.

People rarely set about trying to introduce bird species these days, but introductions still happen because there is so much more movement of animals in trade

Around the turn of the 20th century there was a movement building which was beginning to see the problems associated with a complete open-door approach to introducing alien wildlife species into these unique ecosystems, especially the threats they posed to the delicate native wildlife. In New Zealand, for example, so-called ‘acclimatisation societies’ became legally acknowledged and regulated for the first time in 1867, when an Act was passed ‘to provide for the Protection of Certain Animals and for the encouragement of Acclimatisation Societies in New Zealand’. While it had previously been legal for anyone to introduce any animal they wanted, new legislation deemed it to be forbidden to introduce ‘any fox, venomous reptile, hawk, vulture or other bird of prey’.

It wasn’t until three decades later that a ban on the unauthorised introduction of ‘any animal or bird whatsoever’ was introduced. The 20th century then saw a series of Acts – such as the Animals Protection Act of 1907, the 1921/22 Animals Protection and Game Act, and the 1953 Wildlife Act – with the specific intention of protecting the pre-European, native flora and fauna from potentially threatening invasives. Sometimes these got mixed, such as with the skylark, a bird introduced to New Zealand in the 1860s and 1870s, which has subsequently been proved to cause significant damage to crops. But local opposition to eradicating the bird is high, since the species is now common to many generations of European settlers who tend to think of it as a native species.

Fig 2 newLocations of origin and introduction for bird species with introduced populations (Image: Blackburn, et al)

A new study led by a team of researchers at University College London (UCL) has now produced the first global map of alien bird species, which shows just how much historical acclimatisation had an impact on the spread of invasive fowl. The researchers collected and analysed data on the movement of almost 1,000 alien bird species between the years 1500 and 2000. Their findings from 1500 until 1903 show that New Zealand became a hotspot for invasive species at this time. This was mainly thanks to the efforts of British expatriates shipping duck, geese, swans, pheasants, grouse and partridge to distant regions such as South Australia, India and South Africa. The UK itself also became an alien hotspot during this time, thanks to exotic birds being shipped home around the same time.

Essentially, it is the work of human activity which has been the principle driver of the introduction of alien bird species over the past five centuries. In recent years (1983 to 2000), the modern exotic bird trade has seen places such as Florida, Spain, the Gulf States and richer locations across Asia become hotspots for alien birds. Overall, New Zealand joins Australia, Taiwan, Hawaii, Japan, Hong Kong, parts of the Caribbean and the Mascarene Islands off Madagascar as possessing the world’s greatest ‘alien bird species richness’. Furthermore, the researchers also found that those parts of the world where native species populations are healthiest are also where alien species have most been able to settle and thrive since introduction.

Fig 4Global map of alien bird species richness. Colder colours indicate lower bird species richness, while warmer colours represent higher richness (Image: Blackburn et al)

‘The term “the rich get richer” certainly applies here,’ observes lead author Tim Blackburn, from the Centre for Biodiversity and Environment Research at UCL. ‘Areas that are good for native birds are also good for alien birds. This isn’t a new observation, but it’s the first time we’ve been able to show it factoring out the key effects of historical human actions.’

The study found that more bird introductions (935 introductions of 324 species to 235 countries) were made in the 17 years between 1983 and 2000 than in the 403 years between 1500 and 1903. ‘The global bird trade continues to grow,’ continues Blackburn, ‘which means we can certainly expect alien species richness to continue to grow in the foreseeable future. People rarely set about trying to introduce bird species these days, but introductions still happen because there is so much more movement of animals in trade. It’s a worry because aliens may threaten the survival of native species.’

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