Divided Skies: Lesser Kestrel Lineages Face Unequal Climate Futures
A new study has revealed starkly different vulnerabilities to climate change between Asian and European populations of the Lesser Kestrel
Two lineages, two fates
The Lesser Kestrel, a small migratory falcon spanning the Afro-Palearctic flyway, is not one cohesive species unit after all. Groundbreaking genomic research has uncovered that this charismatic raptor actually comprises two evolutionarily distinct lineages - a European one and an Asian one - with diverging ecological traits, genetic adaptations, and, crucially, responses to climate change.
Using genome-wide SNP data from 119 individuals across 16 breeding populations, researchers established that the European (Western) and Asian (Eastern) lineages are separated by a significant genetic barrier corresponding roughly to the Caucasus Mountains. Though some low-level gene flow persists, the two groups have clearly adapted to different climatic and ecological conditions over millennia.
The European lineage is more associated with croplands and urban nesting sites, whereas its Asian counterpart relies more on natural grasslands and avoids human settlements. The study confirmed that these differences reflect real ecological divergence, with almost no climatic niche overlap between the two groups in either their breeding or non-breeding ranges.
Historical divides shaped by ancient climate
The split between the two lineages likely occurred around 40,000 years ago during the Last Glacial Period. Genomic analyses showed both lineages suffered population declines during glacial cooling but diverged significantly in their subsequent recovery patterns.
While the European lineage benefited from the spread of agriculture and expanded its range during the African Humid Period, the Asian lineage did not undergo comparable growth. Instead, its effective population size remained more static, likely due to its continued reliance on colder, less modified habitats and longer migration routes.
Forecasting the future: unequal climate burdens
When modelling future distributions under both moderate and extreme warming scenarios, the researchers found that the European lineage is likely to expand its breeding and non-breeding ranges northward. In contrast, the Asian lineage is projected to face substantial contractions, particularly in its westernmost populations.
Moreover, birds from the Asian lineage already migrate around three times as far annually as their European counterparts. Climate-driven shifts in breeding and wintering habitats are expected to increase this burden further, unless new, closer non-breeding grounds become viable. Genetic offset analyses suggest that Asian populations, especially those near the contact zone with Europe, face the greatest challenges adapting to rapidly shifting conditions.
Conservation implications: beyond the species level
This study underscores a critical lesson for conservation planning: not all populations within a species respond the same way to environmental pressures. By ignoring intraspecific variation, conservationists risk misjudging vulnerability and missing key opportunities to preserve diversity.
For the Lesser Kestrel, the research team suggests that the Asian (Eastern) lineage should be treated as a distinct Evolutionarily Significant Unit (ESU) - one that is demonstrably more vulnerable to climate-driven maladaptation. Conservation strategies should reflect this, ensuring adequate monitoring, habitat protection, and, where necessary, facilitating gene flow or aiding range shifts.
Meanwhile, even the relatively secure European lineage remains vulnerable to changes in land use, particularly the intensification of agriculture and increasing heatwaves during the breeding season. As climate change accelerates, both lineages will require active and tailored management to ensure their long-term survival.
June 2025
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