Bird populations across North America are declining, according to recently published studies based on long-term biological data collected by volunteers over decades. Until now, however, there has been mostly speculation about what is causing this decline and whether it is accelerating or slowing. Yet acceleration can be an essential signal of environmental change. The causes of the accelerating deterioration in birds are examined in a study by Francoise Leroy and Petr Keil from the Faculty of Environmental Sciences at CZU, carried out in collaboration with Marta Jarzyna of The Ohio State University. It is based on 35 years of research across 1,033 survey routes across the USA and Canada, and it was published on February 26, 2026, in the prestigious scientific journal Science.
The researchers focused on 261 bird species (out of roughly 1,100 in total) from 54 families across ten different habitat types. For 122 species (47%), they recorded a significant decline in abundance, overall averaging 15% and occurring at more than three-quarters of the locations. Hotspots of bird decline are mainly in the southern and warmer parts of North America, such as Florida, Texas, Louisiana, and Arizona. The steepest losses were found among species in open landscapes, urban environments, wetlands, and open woodlands.
The new and crucial finding, however, is that half of the declining bird species (63 species) are now experiencing an accelerating year-to-year decrease. This trend was observed mainly in regions with the most intensive agriculture. In summary, bird abundance is declining almost everywhere, and climate change is likely contributing to this decline. The acceleration of the decline, however, is linked to agricultural intensity. The effects of climate change and agrarian intensification, therefore, combine.
“The results of our analysis are unequivocal, and we should bear them in mind in nature conservation. Agricultural intensity across large areas of arable land, together with the widespread use of pesticides and fertilizers, substantially accelerates the decline in bird numbers. The fact that we are presenting an analysis of North American data does not mean the same cannot apply in Europe. After all, European studies have been showing for some time that birds of agricultural landscapes are among the most threatened,” Petr Keil notes.
The results of the study were assessed by ornithologist Václav Zámečník, who did not participate in it but has long addressed this topic in a European context: “As documented by the results of pan-European monitoring of common bird species, between 1980 and 2024 alone, the abundance of farmland birds in Europe fell by nearly 60 percent. According to a wide range of expert studies, the main driver of their decline is the intensification of farming. A major threatening factor is the application of various chemical substances to fields. Pesticides in particular significantly reduce birds’ food resources. Negative impacts have also come from landscape changes since the second half of the 20th century, when extensive monocultures replaced a diverse mosaic of fields with a high share of non-productive areas. In recent years, this trend has been further amplified by climate change, which across Europe has led to shifts in breeding ranges and, for some bird species, changes in migratory routes. Locally, prolonged heatwaves can also reduce food availability and thus contribute to increased chick mortality.”