Matt Walker, BBC News 4 Dec 09;
The Iron Curtain that divided Europe for 46 years left an indelible imprint on the continent's wildlife.
The isolation of Eastern Europe meant that far fewer alien bird species colonised it, scientists have found.
Restrictions on the movement of people and trade into Eastern bloc countries prevented the birds entering.
While westerners imported exotic birds such as parrots and weavers, people in Eastern Europe introduced just a few game birds that were good for hunting.
The discovery is published in the journal Biological Conservation.
"We obviously do not want to go back to the Iron Curtain days. However, there are some important policy lessons," says Professor Salit Kark, who conducted the research with colleagues based at The Hebrew University of Jerusalem, Israel.
Invasive species remain a significant threat to biodiversity, she says.
"The Iron Curtain somewhat protected the more isolated Eastern bloc from invaders."
"On the other hand, the co-operation today across borders opens more ways to invasion. But it also allows us to address this problem together."
Prof Kark's team initially helped compile an inventory of alien invasive species in Europe.
They added birds to the database, relying on reports, published papers and historical records compiled by birders.
When they analysed the database, they were surprised to find that human activity has a bigger impact on bird introductions than either climate or latitude.
And that impact was exaggerated by the erection of the Iron Curtain.
"During the Cold War, few bird species were introduced into the Eastern bloc, while the West received many more," Prof Kark says.
In Western Europe, the number of non-European bird species introduced steadily rose from 36 before the Cold War had begun, to 46 during the period from 1945 to 1991, to 54 after the Cold War ended.
In Eastern Europe, the number decreased from 11 species introduced before the Cold war to just five during.
Faunal improvement
During the Cold War, people introduced significantly more exotic species such as parrots, weaver-finches and weavers into the West.
These cage birds were brought in as pets, to supply zoos and as part of a general policy of "faunal improvement."
In the East, far fewer birds were introduced. Those imported were mainly game birds, such as partridges, pheasants, ducks and geese that could be hunted for food.
Across the continent, most introduced bird species have remained within the initial country they were imported into.
That means there is still time for policy makers across Europe to take action to prevent them spreading further, say the researchers.
But 14 of the 121 species have spread into neighbouring countries.
"Many of them, such as the rose-ringed parakeet from India, and the monk parakeet from South America, are spreading fast," says Prof Kark.
Urgent action
The realisation that large political and trading blocs can have such impact can be used in a positive way, she says.
"The fact that EU countries are co-ordinated means they can act together, make policy decisions and address them together."
As trade and the movement of people increases across Europe, says Prof Kark, and many former Eastern European countries are integrated into the EU, it becomes more urgent to establish policies to prevent a new flow of exotic species into regions that were once isolated.
The same principles apply to any region where trade has expanded dramatically, such as China and India and developing countries, she adds.
"These countries may not yet have developed the policies to deal with alien species, but they have an opportunity to learn those lessons before more alien species are introduced."
"However, the timing is urgent and countries need to start enacting policies soon."
