Amazonian birds under threat from road expansion

Ornate Hawk-Eagle (Spizaetus ornatus). Credit: Santiago Restrepo Calle

Increased road construction is reducing bird biodiversity in Brazil's Amazon rainforest, according to a new study.

Reporting in the journal Proceedings of the Royal Society B, scientists examined the links between density of road networks in Pará, which is a Brazilian state found in the North of the Amazon rainforest, and the richness of forest bird species.

Results show that between 2000 and 2008 approximately 2773 kilometres of new roads were constructed. During this same period each of the 18 catchments studied lost an average of 83 species of birds

Senior researcher Dr Robert Ewers from the Department of Life Sciences at Imperial College London said: “Current estimates suggest that a massive 27,000 more kilometres of roads will be constructed in the Pará region by 2031. With little or nothing in the way of environmental assessment of how this colossal construction will impact biodiversity, it is even more crucial that we look at the impacts of road building.”

Building roads usually involves destroying birds’ habitats. The new research also explores other less obvious consequences, such as creating barriers between habitats, disrupting birds’ movement. Lead researcher Dr Sadia Ahmed, who carried out the research while working at Imperial and who is now working at Microsoft Research, said: “There are some species of birds that will just not cross even the very narrowest of roads. This not only splits up a population, but can also cause inbreeding and reduce genetic variation among species.”

Increased road volume also changes birds’ environments, altering light and vegetation structure close to the edge of the forest, and increases the exposure of birds to human activities.

In addition, the scientists found that road construction acted as an early warning for future habitat degradation, as improved transport links can increase human activities, such as timber logging. Increased logging reduces forest cover and changes environmental conditions, making the environment unsuitable for certain species. For example, reducing the forest canopy leads to a surge in forest floor vegetation – an incompatible habitat for species such as the Musician Wren (Cyphorhinus arada), which in the new study was only found in areas with fewer roads.

“Looking at areas with increased road networks, but as of yet little change in forest cover, could help us identify frontier regions that are likely to experience biodiversity loss in the future,” explains Dr Ahmed.

Prior to the new study, there had been little research looking at the specific effects of road network growth on biodiversity, beyond quantifying habitat loss.  The scientists hope their findings will ultimately help maintain the richness of bird species in Brazil’s Amazon rainforest. 

Dr Ahmed stressed: “It is particularly important to look at biodiversity in the Amazon because this vulnerable rainforest is one of the world’s most species rich areas and species here are becoming increasingly endangered and more and more exposed to human activities.”

Dr Ewers added: “We know that building completely new roads in a previously roadless area is much more damaging to the environment than intensifying an existing road network. Rather than allowing road networks to spread We should put more effort into working with local communities and government to identify locations where new roads will be less damaging to habitats and where they will also help people to find sources of income that are less problematic for wildlife than logging or hunting. For example, intensifying roads in agricultural landscapes has been shown to help promote increases in agricultural yields.”

The scientists used a metric called ‘roadless volume’ (RV) to investigate the links between road density and bird biodiversity. RV counts the amount of space that lies between roads and can determine how far a road has penetrated into an undeveloped area. When more roads are built, RV decreases. They used satellite images to calculate changes in RV between from 2000 to 2008.

The study examined 18 catchments across the Pará region in the Northern Amazon and recorded more than 384 different species of birds.

The research was funded by Microsoft Research, the Grantham Institute for Climate Change and the European Research Council.

REFERENCE: Ahmed S. E. et al. ‘Road networks predict human influence on Amazonian bird communities’. Proceedings of the Royal Society B. October 2014. http://dx.doi.org/10.1098/rspb.2014.1742