Infrastructure, and climate change linked to huge migratory bird declines

Migratory birds are declining globally due to the way humans have reshaped the landscape in recent decades, according to new research from the University of East Anglia.

The study published in the journal Global Ecology and Biogeography reveals that population declines have been greatest among species that migrate to areas with more human infrastructure (roads, buildings, power lines, wind turbines), as well as higher population densities and levels of hunting. Habitat degradation and climate change have also played a role in driving long-term declines.

The research team hopes their work will help inform how best to target conservation efforts. Dr James Gilroy, from UEA's School of Environmental Sciences, said: "We know that migratory birds are in greater decline than non-migratory species, but it's not clear why. "We wanted to find out where in their life cycles these migratory species are most exposed to human impacts."

The research team identified 16 human-induced threats to migratory birds, including infrastructure associated with disturbance and bird strikes, conversion of land from natural habitat to human land use, and climate change.

Advances in satellite imagery allowed the team to map each of the 16 threats across Europe, Africa and West Asia. The team also created the first large-scale map of hunting pressure across the region.

A total of 103 migratory bird species, including many rapidly declining species such as the turtledove and the common cuckoo, were studied using large-scale datasets. The team calculated "threat scores" for factors such as habitat loss and climate change, at breeding sites as well as non-breeding ranges.

They then explored relationships between these threat scores and bird population trends calculated from 1985 to 2018 by the Pan-European Common Bird Monitoring Scheme (PECBMS).

Study author Claire Buchan says: "We found that human modification of the landscape in bird ranges in Europe, Africa and West Asia is associated with declines in numbers of more than 100 Afro-Eurasian migratory birds. By landscape modification, we mean things like roads, buildings, power lines, wind turbines, anything that isn't naturally present.

One of the biggest impacts appears to be caused by things that would kill a bird outright, for example flying into a wind turbine, a building, being electrocuted on a power line, being hit by a vehicle, or being chased. We found that exposure to these human-induced 'direct mortality' threats on birds' wintering ranges is reflected in population declines in breeding birds."

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