US and Canada have lost three billion birds since 1970

More than one in four birds have been lost across diverse groups and habitats, in what researchers describe as a 'wake-up call'

The US and Canada have lost more than one in four birds - a total of three billion - since 1970, culminating in what scientists who published a new study are calling a "widespread ecological crisis".

Researchers observed a 29% decline in bird populations across diverse groups and habitats - from songbirds such as meadowlarks to long-distance migratory birds such as swallows and backyard birds like sparrows.