Conservation's Blind Spot: The Wintering Grounds
GPS tracking of Eurasian Stone-curlews from western France reveals complex, varied migratory strategies and raises fresh conservation concerns about wintering habitat change
Unravelling a cryptic migrant’s secrets
Stone-curlews are masters of camouflage and concealment, not just on the ground but also in science. While their breeding ecology in Europe is fairly well known, their full annual movement cycle has remained something of a mystery. Now, thanks to nearly a decade of GPS tracking, researchers have mapped the migratory behaviour of Eurasian Stone-curlews (Burhinus oedicnemus) breeding in central-western France, revealing striking differences between individuals - and surprising consistencies too.
Using high-resolution GPS tags fitted to 32 adult birds between 2012 and 2020, the study followed 20 individual migrants across multiple seasons, tracking their routes, stopovers, and wintering grounds in unprecedented detail. Despite all birds coming from the same breeding population, they migrated to widely scattered winter sites - from Portugal and Spain to Morocco and Algeria - and showed markedly different strategies for timing, distance, and stopover use.
Yet while strategies varied across the population, individual birds showed high repeatability in their own behaviours year on year. This suggests a strong degree of behavioural fidelity despite the absence of strong environmental constraints that drive consistency in other long-distance migrants.
Neither here nor there: flexible but faithful travellers
The Stone-curlews tracked in this study all undertook relatively short migrations (typically 1,100–2,200 km), travelling exclusively by night and avoiding major barriers like the Pyrenees and the Mediterranean wherever possible.
Spring and autumn journeys were of similar duration - a contrast to many other migratory waders, where spring migration is typically faster to facilitate early arrival at breeding sites. Instead, Stone-curlews migrated over 8–12 days on average, with few and brief stopovers. Many individuals took a straight path with no stops at all. Despite this apparent flexibility, birds showed strong individual consistency in their chosen routes, timings, and wintering locations across years.
Wintering ranges varied in size but were generally small (averaging 6.2 km²) and tightly clustered. Birds tracked over multiple winters showed site fidelity on par with their breeding grounds, with over 70% overlap in core winter home ranges between years.
Why so different - and why does it matter?
This combination of high inter-individual variability and high intra-individual repeatability is unusual and may reflect the relatively low selective pressure acting on migratory traits in this population. Unlike Arctic-breeding waders, Stone-curlews nesting in temperate France face less seasonal constraint and have more flexibility to adjust migration timing and routes.
Such behavioural plasticity might offer resilience in the face of environmental change. But it also complicates conservation planning, which often assumes shared migratory pathways or bottlenecks. The diversity of routes and destinations used by French Stone-curlews means threats could arise anywhere along a wide swathe of Iberia and North Africa.
And the situation is changing. Agricultural landscapes in southern Spain and Morocco - key wintering areas for many of the tracked birds - are undergoing rapid transformation due to drought, irrigation intensification, and the spread of solar farms. While current wintering conditions appear adequate, they may not remain so for long.
Breeding grounds still the priority - for now
Despite these emerging threats, the study concludes that the immediate drivers of population decline in this French Stone-curlew population likely lie on the breeding grounds. Ongoing farmland intensification, habitat homogenisation, and loss of open arable mosaics are probably exerting greater pressure than migration or wintering conditions - at least for now.
Nonetheless, with some birds already showing signs of residency and the prospect of more becoming sedentary as winters warm, future conservation efforts will need to address both ends of the migratory chain. The Stone-curlew’s apparent flexibility could buy time - but not indefinitely. Long-term survival may depend on pre-emptive action in both the fields of France and the plains of Iberia and North Africa.
Why this study matters
Long-term datasets from tropical regions are rare, making this century-spanning study especially valuable. The subtle but measurable changes in body shape and size serve as indicators of broader ecological shifts and highlight the importance of continued monitoring. The study calls for further investigation into the mechanisms behind these changes, combining ecological, behavioural, and physiological research to fully understand how tropical birds - and biodiversity more generally - are coping with a warming world.
July 2025
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