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Do Eurasian Curlews follow the same migration route every year? Not exactly. A 2026 GPS-tracking study found that individual Eurasian Curlews usually return to the same breeding and wintering areas, and that each bird’s routes are more similar to its own routes in other years than to routes flown by other curlews. The flown path still changes between years, especially in autumn. That combination—strong personal routines with some flexibility—is why researchers are concerned that rapid environmental change could make a once-successful route less suitable.
What the study actually found
The peer-reviewed study, published in Communications Biology in 2026, analyzed high-resolution GPS records from 94 Eurasian Curlews (Numenius arquata). Birds were tagged between 2014 and 2021, and some individuals were tracked for as many as seven consecutive years. This is a long record for individual migration behavior, but it remains a study of tagged birds and the population they represent—not proof that every Eurasian Curlew worldwide follows one route.
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Researchers measured 24 features of the birds’ annual cycle. These included where birds bred and wintered, migration timing, the number and duration of stopovers, distances traveled, and how closely routes matched from one year to the next. Twenty-two of the 24 measures showed statistically significant repeatability.
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| Finding | What it means |
|---|---|
| 94 tagged curlews | The evidence comes from individually tracked birds, not a complete census of the species. |
| Up to seven consecutive years for some birds | Researchers could compare the same individual across multiple migrations. |
| 24 annual-cycle measures tested | The analysis covered locations, timing, stopovers, distances and route similarity. |
| 22 measures significantly repeatable | Most aspects of annual movement showed a consistent individual pattern. |
| Breeding and wintering sites had the strongest repeatability | Birds were especially faithful to familiar endpoint areas. |
“The same route” is an overstatement
The headline result needs three distinctions. First, the study did not find one shared route used by all Eurasian Curlews. Second, it did not find that an individual bird traced an identical line every year. Third, it did find that an individual’s route choices were more alike across its own years than they were to routes chosen by other birds.
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Stable endpoints, changing paths
Breeding and wintering locations were highly repeatable, with reported repeatability values close to 1 for latitude and longitude. In practical terms, a bird often returned to the same general breeding area and the same general wintering area. The straight-line distance between those areas was also more repeatable than the actual distance the bird flew.
That difference matters. A curlew can connect the same two seasonal areas by taking a different coastal segment, bypassing a site, adding a stopover or changing the amount of ground covered. The endpoints may stay familiar while the route between them shifts.
Individual signatures, not a single species-wide line
When researchers compared consecutive years, the geographic locations of migration routes varied. Yet within-individual similarity was significantly greater than between-individual similarity. A useful way to state the result is: curlews do not all migrate the same way, but a given curlew tends to be more like itself from year to year than like its neighbors.
Spring and autumn are not equally consistent
All measured spring-migration and stopover parameters were significantly repeatable. Autumn measures were less repeatable. The authors suggest that variable breeding success may contribute to that difference: a bird’s condition, timing and needs after breeding can vary more from year to year, altering its choices in autumn.
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Where these tracked curlews traveled
The study concerns the East Atlantic Flyway population. In the tagged sample, wintering locations extended from the southwestern Iberian Peninsula north to Scotland, and from Ireland east to the Wadden Sea of Denmark and Germany. Breeding locations ranged from western France to areas northeast of the Ural Mountains in Russia.
Migration was concentrated along the Atlantic and North Sea coasts. Across the Baltic region and farther east, movements spread over a broader front rather than following one narrow corridor. More than half of the tagged curlews used the Wadden Sea as a stopover. That makes the Wadden Sea an especially important refueling area for this sample, not a claim that every curlew in the flyway uses it.
These boundaries describe the birds included in this tracking work. They should not be treated as a complete range map for the species, and they should not be transferred to the Eastern Curlew (Numenius madagascariensis) or the Far Eastern Curlew, which are different species.
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Repeated use of the same sites can be advantageous when conditions remain reasonably predictable. A bird that has previously used a marsh, estuary or coastal flat may already have information—acquired through experience—about food availability, predators, roosting places and the timing of local conditions. Returning can reduce the need to search for suitable habitat during an energetically expensive journey.
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What a familiar stopover can provide
- Known food opportunities: intertidal areas and wetlands can be used efficiently when a bird has encountered them before.
- Known roosts: safe high-tide resting places are valuable during stopovers.
- Lower search costs: a bird can spend less time prospecting for habitat and more time feeding or resting.
- Predictable connections: learned sites can form a dependable sequence between breeding and wintering areas.
Faithfulness is therefore not automatically a weakness. It can be an efficient strategy shaped by learning and survival in familiar landscapes.
Why repeatability could become dangerous
The study’s “potentially dangerous” implication is about reduced flexibility, not observed injuries or deaths. The researchers did not show that a tagged bird was harmed because it followed a traditional route, nor did they demonstrate a climate-driven route failure.
The concern is a mismatch between a bird’s learned routine and a rapidly changing environment. If a stopover loses food, a roost becomes unsafe, a wetland dries, or the timing of prey availability shifts, a bird that returns to the same place may not immediately switch to a better alternative. A route that worked under familiar conditions can become less profitable while the bird’s behavior remains comparatively consistent.
Three kinds of change that could create a mismatch
- Habitat change: reclamation, disturbance or altered water levels can reduce the quality of a traditional stopover.
- Timing change: weather and seasonal conditions can shift the period when food is most abundant.
- Short-term disruption: an unusual event can make a site unsuitable even if it remains usable in most years.
The authors describe this as possible maladaptive behavior in response to short-term change. They call for site managers to observe the issue carefully rather than assuming that repeated use proves a site remains suitable.
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What the study does—and does not—prove
| The evidence supports | The evidence does not establish |
|---|---|
| Individual curlews often repeat breeding and wintering areas. | Every Eurasian Curlew follows the same route. |
| Most of the 24 measured annual-cycle traits were repeatable. | All traits are equally fixed. |
| Individual routes resemble one another more than routes of different birds do. | An individual flies an identical line every year. |
| Spring movements were generally more repeatable than autumn movements. | A single cause for the spring–autumn difference has been proven. |
| Repeated routines may limit responses to environmental change. | The tracked birds were shown to suffer harm or long-term population loss because of route fidelity. |
| The tagged sample used the East Atlantic Flyway, with the Wadden Sea used by more than half of birds. | The sample provides a complete global distribution map for the species. |
How to interpret the near-threatened status
The study describes the Eurasian Curlew as near-threatened and notes a negative population trend across the East Atlantic Flyway. The material reviewed for this article does not provide a current population total or a quantified percentage decline, so those figures should not be inferred from the tracking results.
Near-threatened status also does not mean that every individual is in immediate danger. It indicates a conservation concern at the species or population level. The movement findings add a behavioral dimension: protecting a bird requires protecting not only its breeding grounds, but also the wintering areas and stopovers that its established annual schedule depends on.
What conservation managers can do with this information
Protect the whole chain of sites
A curlew may depend on several locations separated by thousands of kilometers. Conservation that safeguards only the breeding area can fail if a key coastal stopover or wintering wetland is degraded. The Wadden Sea’s frequent use in this sample illustrates why staging areas deserve the same attention as seasonal endpoints.
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Managers can monitor whether birds continue arriving at traditional sites while spending less time there, departing in poorer condition, changing their stopover duration or moving on without adequate feeding. Such observations do not by themselves prove maladaptation, but they can identify places where food, disturbance or water conditions need investigation.
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Maintain alternatives, not just one protected site
Because routes show some plasticity, a network of suitable wetlands and coastal areas may give birds options when one site becomes temporarily poor. The objective is not to force curlews onto a new route, but to preserve enough functional habitat for individual birds to adjust when conditions require it.
Track multiple cohorts over longer periods
The authors state that understanding adaptation to long-term environmental change will require further work, preferably involving several cohorts of individuals. One cohort can reveal repeatability; multiple cohorts and longer records are better suited to detecting whether behavior changes as conditions change.
How researchers measured “repeatability”
Repeatability is a statistical description of how consistently differences among individuals persist across observations. A high value means that birds tend to retain their relative pattern—for example, repeatedly using similar breeding coordinates—rather than behaving as interchangeable members of one population.
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteIt does not mean a value is literally identical every year, and it does not measure whether the behavior is beneficial. A highly repeatable route can be useful, neutral or harmful depending on conditions. In this study, the highest repeatability occurred for breeding and wintering site use, while route geography and some autumn measures retained more variation.
How readers can explore migration evidence
The UNEP page for the CMS Eurasian-African Bird Migration Atlas describes an interactive mapping tool that combines ringing data collected over more than 100 years on 300 species with satellite, GPS-GSM and geolocator tracks for more than 100 species. It is useful for seeing how movement evidence is assembled across countries and methods; the description does not establish a physical book edition.
The British Trust for Ornithology’s Curlew information page brings together evidence from bird portals, ringing schemes and tracking studies, and points readers toward European movement and migration resources. These sources can provide broader context, but they should not be read as replacing the individual-level GPS analysis described here.
Quick Recap
Key takeaways
- Eurasian Curlews do not all follow one identical migration route.
- Individual birds show strong annual routines, especially in breeding and wintering site choice.
- Routes change between years, but a bird’s routes are more similar to one another than to those of other birds.
- Spring movement was more consistently repeatable than autumn movement in the study.
- More than half of the tagged birds used the Wadden Sea stopover within this East Atlantic Flyway sample.
- The possible danger is inflexibility when habitat or timing changes—not demonstrated harm from route-following itself.
- Long-term adaptation remains unresolved and needs multi-cohort monitoring.
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