AN EXTENSIVE NEW database has mapped the movements of “alien” bird species for the first time.
Led by a team at the University College London (UCL), researchers investigated global data on the movement of nearly 1,000 invasive bird species between 1500 and 2000. They found that human activities are the main influence on how many invasive bird species live in an area, but that they are most successful in areas already rich with native bird species. The study is published in the journal PLOS Biology.
Invasive species threaten global biodiversity by predating or outcompeting native species and by carrying diseases. Three listed by the International Union for the Conservation of Nature (IUCN) as being in the worst 100 invasive species are the Indian myna, the common starling and the red-vented bulbul.
More than half of all known bird introductions were found to occur after 1950 – such as ring-necked and monk parakeets, common waxbill and Java sparrow – and researchers say this trend is expected to continue as more alien birds are introduced where people have more disposable income.
The data took three years to compile and cross-check, and another three years to analyse for patterns in the context of historical events: acceleration after World War II due to growth in the exportation trade; and the Acclimatisation Societies moving birds such as ducks, geese, pheasants, partridge and pigeons to colonies. Other factors include natural environmental variation.
Results showed that more bird introductions (935 introductions of 324 species to 235 countries) were made in the 17 years between 1983-2000 than occurred in the 403 years from 1500-1903.
Supervising author, Professor Tim Blackburn, who completed the analysis with first author Dr Ellie Dyer, said: “Our work shows why humans have been moving these ‘alien’ bird species around for the past 500 years – primarily through colonialism and the increasingly popular cage bird trade – and why some areas end up with more species than others.”
However, the team also found that areas that are good for native birds are also good for alien birds.
Prof Blackburn explained: “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 global bird trade continues to grow, which means we can certainly expect alien species richness to continue to grow in the foreseeable future.
“It’s a worry because alien species may threaten the survival of native species.”