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The US and Canada have lost almost 3 billion birds since 1970 due to human activities, in a dramatic decline researchers are calling an “overlooked biodiversity crisis”.

This is the first time researchers have attempted to estimate the actual population changes in breeding birds there, and suggests that North America has seen more than a quarter of its birds disappear in recent decades.

Kenneth Rosenberg of Cornell University in New York says: “It is our first look at the magnitude of the loss. The only thing we have to compare it with is the estimate of 2 to 3 billion passenger pigeons in North America, which went to zero in less than 100 years.”

Rosenberg and colleagues looked at 529 species between 1970 and 2017. They used data from and , cross-referenced with records of the biomass of migrating birds from 148 radar stations, to build a model of population estimates.

The most common species, such as starlings, have been hit the hardest.  More than 90 per cent of the net loss of 2.9 billion birds occurred across just 12 families, including sparrows, warblers and blackbirds.

“The big surprise is that the loss was pervasive across common species,” says Rosenberg. Because they are more abundant, common birds are crucial for processes necessary for the normal functioning of ecosystems, such as pollination.

Habitat loss and degradation are the biggest drivers of population declines, particularly for grassland birds. The attitude of the US government towards bird protections today is “the worst we’ve seen in a very long time”, says Rosenberg. A key battleground is the .

Author and birder Jonathan Franzen says the paper is alarming but unsurprising. He told 91av: “We need to pay a lot more attention to immediate, present-day threats to the natural world – all the more so because, unlike climate change, these threats can be meaningfully addressed at the local and regional level, through achievable conservation actions.”

The Audubon Society says it is declaring a “bird emergency” and the crisis requires political leadership and individual action.

Richard Gregory at the Royal Society for the Protection of Birds in the UK says although there are weaknesses in the datasets the researchers had to rely on, they are the best available. Similar bird losses have been reported in Europe, he adds.