This very common bird is gradually losing its unique colors

The Buzzard, so familiar and yet so “variable”

It’s a bird we see so often that we eventually stop paying attention to it. Perched on a fence post, soaring over farmland, or performing spectacular dives during its courtship displays, the common buzzard is part of the landscape. Yet its nickname, the “variable buzzard,” is no coincidence. Its plumage exhibits such a wide variety of patterns—both light and dark—that some observers have sometimes mistaken these different colorations for distinct species.

Now, a new study reveals that this famous variation is fading. Thanks to years of observations and photos shared online by nature enthusiasts, scientists have been able to map the color of buzzards across Europe for the first time. Their analysis is clear: buzzards with intermediate coloring are becoming increasingly common, while the lightest and darkest birds are seeing their share of the population decline.

When Thousands of Citizens Map Europe

This study is a true testament to citizen science. Researchers at the Max Planck Institute for Biological Intelligence and their collaborators compiled nearly 100,000 buzzard sightings, collected from the early 2000s through 2022. This monumental database is the result of the work of thousands of enthusiasts.

Some of this information came from a dedicated portal created by Elena Kappers and Bart Kempenaers, where observers could rate the color of buzzards on a seven-point scale, ranging from very light to very dark. The team also analyzed thousands of publicly available photos uploaded to platforms such as iNaturalist, Observation.org, and Ornitho.it. At the same time, the researchers cross-referenced these observations with satellite data on climate, vegetation, and soil type.

This approach allowed the team to test whether the major ecological “rules” regarding animal coloration applied to the buzzard. For example, the idea that darker birds are found in forests for camouflage, or in cold regions to better absorb heat, could be put to the test on a large scale.

Colors That Defy Ecological Theories

The map generated from this data revealed a surprising mosaic. Light-colored buzzards are more common in northern and central Europe. Darker birds are more frequent in Brittany and on the Iberian Peninsula, while individuals with intermediate coloring are the majority in southeastern Europe and the British Isles. This geographic patchwork does not clearly correspond to the patterns expected if the environment were the only influencing factor.

Kaspar Delhey, the study’s lead author and a researcher at the Max Planck Institute, highlights this discrepancy. “Strikingly, the ecological theories we tested explained only a very small portion of the color variation in common buzzards. For example, lighter-colored birds tended to be more dominant in colder regions rather than in warmer ones,” he said. So, if climate and habitat are not the main drivers, what is the explanation?

Kaspar Delhey suggests two possible explanations. “The color of the common buzzard is strongly inherited, so these patterns may instead reflect how buzzards recolonized Europe after the last ice age, or be linked to as-yet-unidentified ecological factors—or both,” he explains.

The Slow Standardization of Plumage

The most fascinating aspect of the study lies not only in the distribution of colors, but in their evolution. Previous local studies had already suggested that intermediate-colored buzzards fared better: they survive longer and raise more young than birds with extreme plumage. The new continent-wide data confirm this trend.

The numbers speak for themselves. In 2022, intermediate-colored buzzards accounted for a significantly larger share of the population than in 2000. At the same time, the proportion of dark buzzards fell by 22%, and that of light buzzards dropped by 14%. In other words, while the buzzard remains a very common bird, the color palette that earned it the name “variable” is slowly shrinking.

Fewer colors, less adaptability?

Beyond aesthetics, this loss of color diversity raises a deeper concern. Bart Kempenaers, who heads the Department of Ornithology at the Max Planck Institute, notes that environmental changes may play a role, but do not explain everything. “We found links to environmental changes such as the loss of forest cover, but these only explained part of the picture,” he explains.

The main concern is what this color diversity represents genetically. If the decline in plumage types is accompanied by a decrease in overall genetic variation, this could weaken the species’ ability to adapt to future challenges, whether they be climate change or changes to its habitat.

That is why the research team is calling for more in-depth follow-up studies. The use of genomics and the study of museum specimens could reveal whether this color change is linked to genetic impoverishment, new selective pressures, or a combination of modern and ancient forces.

A Better Understanding of a Bird Thanks to Thousands of Eyes

What makes this study so special is that it would have been virtually impossible without public participation. No single research team could have tracked buzzards across Europe for more than twenty years to build such a vast database. It is a collective achievement.

“What excites me most is what citizen science makes possible—a wonderful collaboration that has allowed us to explore questions that would otherwise be beyond our reach,” says Bart Kempenaers. The buzzard’s “variable” appearance is therefore still a reality; both light- and dark-colored birds can still be observed.

However, the data indicate that Europe is slowly moving toward a more uniform appearance for this bird. And it is thanks to the thousands of citizens who, during their walks, took the time to report their observations that scientists can now track this evolution in real time. The study was published in the journal Ibis – The International Journal of Avian Science.

Source: earth.com

This very common bird is gradually losing its unique colors