That's not what the original paper says. This is why you want to read the actual scientific paper and not the article about it. The researchers, in the article's text, state:
> "Steep declines in North American birds parallel patterns of avian declines emerging globally (14, 15, 22, 24). In particular, depletion of native grassland bird populations in North America, driven by habitat loss and more toxic pesticide use in both breeding and wintering areas (25), mirrors loss of farmland birds throughout Europe and elsewhere (15). Even declines among introduced species match similar declines within these same species’ native ranges (26). Agricultural intensification and urbanization have been similarly linked to declines in insect diversity and biomass (27), with cascading impacts on birds and other consumers (24, 28, 29). Given that birds are one of the best monitored animal groups, birds may also represent the tip of the iceberg, indicating similar or greater losses in other taxonomic groups (28, 30)."
This points to agricultural pesticides having impacts on insect populations, and additionally this mirrors where losses have been most extreme, in grasslands most impacted by agricultural activity:
> "Across breeding biomes, grassland birds showed the largest magnitude of total population loss since 1970—more than 700 million breeding individuals across 31 species— and the largest proportional loss (53%); 74% of grassland species
are declining. (Fig. 1 and Table 1)."
I've made it a habit to always seek out the original paper instead of just reading the 'science journalism' take on it, for reasons like this.
https://www.flatheadaudubon.org/wp-content/uploads/2019/10/R...