For a large collaborative study into ongoing population changes in North America, I tracked bird biomass flows through the US since 2007 with the NEXRAD weather radar network
From the annual biomass passages, long-term trends were estimated, which indicate a large decrease in the number of birds migrating at night over the US.
The total loss in spring passage since 2007 was estimated at 14 +/- 9%. Similar steep declines were found from a comprehensive compilation of ground surveys, including the North-American Breeding Bird Survey, which indicate a loss of 3 billion birds in North America since 1970, or 1 in 4 birds.
The study was published in Science on 4 Oct 2019. Visit https://www.3billionbirds.org/ to download the paper and for more information on the study.
- Rosenberg KV, Dokter AM, Blancher PJ, Sauer JR, Smith AC, Smith PA, Stanton JC, Panjabi A, Helft L, Parr M, Marra PP. (2019) Decline of the North American avifauna. Science, 366, 120-124, DOI 10.1126/science.aaw1313