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Researchers have conducted the world's biggest ever bird survey, recording 971 different species living in forests and cattle pastures across the South American country of Colombia. This represents almost 10% of the world's birds.

They combined the results, gathered over a decade, with information on each species' sensitivity to habitat conversion to find that the biodiversity loss caused by clearing rainforest for cattle pasture is on average 60% worse than previously thought.

Until now, understanding the biodiversity impact of land-use change has generally involved small-scale, local surveys. The researchers say that this approach does not represent the larger-scale damage caused to nature.

When forests are converted to pasture, some species win and others lose. Measuring the biodiversity loss at a local scale does not capture the larger-scale effect of forest conversion, which is occurring across the ranges of many different species. While the same species usually survive on pastureland, a wide range of other species don't, so overall biodiversity is more severely reduced at large scale.

The results are published in .

Professor David Edwards of the University of Cambridge's Department of Plant Sciences and Conservation Research Institute, senior author of the report, said, "This is a really surprising result. We found that the biodiversity loss caused by clearing rainforest for pastureland is being massively underestimated."

He added, "When people want to understand the wider impact of deforestation on biodiversity, they tend to do a local survey and extrapolate the results. But the problem is that tree clearance is occurring at massive spatial scales, across all sorts of different habitats and elevations.

"When we looked at the biodiversity impact of deforestation across 13 different ecoregions in Colombia, we found a 62% greater biodiversity loss than local survey results would indicate."

The study also showed that at least six different ecoregions—that is, regions containing distinct types of plants and animals—must be considered for an accurate assessment of overall biodiversity impact. This is because the species in different ecoregions have different sensitivities to habitat conversion.

Biodiversity offsetting schemes, which aim to compensate for species losses caused by developments in one place by boosting biodiversity in another, rely on accurate measures of biodiversity.

Trees are also being cleared at huge scales in Colombia and other tropical regions to create growing space for major agricultural crops including rubber, oil palm, sugar cane and coffee.

Edwards said, "The food we eat comes with a much greater environmental cost than we thought. We need policymakers to think much more about the larger-scale biodiversity impact of deforestation."

Tropical birdsong recordings

The team studied Colombia's birdlife across its diverse landscapes for over seven years, recording the song of hundreds of bird species to help them identify the species present in landscapes across the country, from pasture to mountain forest. In about 80% of cases, the birds were heard but not seen, requiring the team to make identifications from the sounds alone.

With information about the birds, including their size and diet, the team could predict which other species were likely to be living in the same regions and how they too would respond to deforestation.

A highly biodiverse country

Colombia is home to some of the most beautiful and exotic animal and plant life in the world, with almost one third made up of rainforest.

Particularly biodiverse areas, including the Caqueta moist forests and the Napo moist forests, can have 500–600 different bird species within an area of ten square kilometers—but many of these species have very specific habitat requirements. The study showed that if trees are cleared across their range, these species are likely to die out.

Land-use change, particularly in the highly biodiverse tropics, is one of the main causes of the global biodiversity crisis.