In 2001, scientists released beetles to fight an invasive tree. Years later, an endangered bird had lost 94% of its habitat along one western river

• The breeding grounds of the Southwestern Willow Flycatcher stretch across thousands of kilometres of rivers and streams in the American Southwest, yet much of its habitat has long been difficult to assess in a consistent way.
• Thick vegetation, changing river systems and seasonal drought all make monitoring the small migratory bird a complex task.