Researchers say alien birds are threatening Himalayan biodiversity

New Delhi, January 25

Alien birds are spreading across southeast Asia and could reach India — either due to escaping captivity or after being intentionally released, researchers with the University College London (UCL) warned on Monday.

In a study published in 'Nature Ecology & Evolution', researchers show how the alien species such as the zebra dove are a threat to India, as the Himalayas are particularly prone to the spread of non-native birds.

Native in some of the Southeast Asian countries, the zebra dove (Geopelia Striata) has spread across the region. Now it has alien population in Thailand and Laos, among other countries.

The study says once a bird has established itself as an alien species in a new region, living alongside native birds, it is most likely to continue spreading to other areas where those same native birds are present.

The study improves on the existing methods to predict the spread of alien species.

The researchers found that areas such as the Himalayas and parts of sub-Saharan Africa, which so far have not seen many alien species, could be under threat in the coming decades.

Senior author Alex Pigot of the UCL Centre for Biodiversity and Environment Research said: "Alien species — those that have been introduced to new areas outside their native range — are one of the leading causes of global biodiversity loss. Driven by human actions, alien species also represent a growing threat to food security, human health and many economies. Predicting where they will spread next, so that we can find ways to mitigate the damage, is an urgent global challenge." The researchers reviewed data of 339 bird species which have already become established as alien species outside of their native range, distributed all across the globe.

To see if they could predict, in hindsight, where these alien species had spread, the researchers first investigated how similar areas across the globe are in terms of their existing native bird species — what is called biotic similarity.

Lead author Rebecca Lovell, who completed the work as part of her Master's degree in Pigot's lab, explained: "If environmental conditions allow native birds to move freely between two places, then alien species may also be able do the same.

"To test this idea, we were looking at birds that we already know which have been introduced into new regions by human actions, and have successfully established themselves as alien bird populations and spread, sometimes far beyond their initial introduction site." The researchers found that by considering the set of native bird species present in the location that first hosted an alien bird, they could accurately predict where else that alien bird can spread to.

This type of biotic similarity (which they call environmental resistance, where an area with a very different makeup of native birds exhibits high environmental resistance) is a stronger predictor of the spread of already established alien birds than comparing an area's climate to the conditions where an alien species lives in its original native range.

Having verified their approach, the researchers then identified the areas that appear to be at risk of invasions by birds that are already established as aliens elsewhere, despite not yet having many alien species.

In particular, parts of Southeast Asia stretching from Sumatra, through the Malay Peninsula, southern China and along the Himalayas as well as sub-Saharan Africa appear to be at risk.

These areas currently have just a handful of alien bird species that have spread far beyond major urban areas, but are at risk from the spread of up to 10 times as many alien bird species — without even including the risk from alien species that have yet to be introduced anywhere new.

Pigot added: "While this paper doesn't address where new alien species are likely to be introduced by humans in the future, we expect this will be dictated by economics, societal behaviour and biosecurity measures.

Co-author Tim Blackburn of the UCL Centre for Biodiversity and Environment Research and the Institute of Zoology said: "A high-profile example here is the parakeets that were introduced in London and have spread to nearby areas in the south east of England. In the longer term, our findings suggest their next homes could be other European areas that already have the same sort of birds, which suggests that those environments satisfy a range of different requirements for the species." IANS

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