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Western Marsh Harriers Preferred Greener Stop Sites During Sahara Crossings

Male western marsh harrier in flight
Research · Ecology

Western marsh harriers (Circus aeruginosus) crossing the Sahara did not pause randomly in the desert. They used relatively greener sites for short daytime stops, while the pattern of interruptions also varied with wind conditions and proximity to subsequent night roosts. The study used GPS/GSM tracking and was first published online on 14 January 2026 in Ardea.

The researchers analysed migration tracks collected from 2019 to 2023 as the harriers crossed hyper-arid parts of the Sahara, combining the GPS/GSM tracks with satellite-based vegetation measurements and wind data.

Harriers preferred greener stop sites

Stop-site selection was associated with the Normalised Difference Vegetation Index (NDVI), a satellite measure that reflects the presence and greenness of vegetation. The harriers preferred sites with higher NDVI values, showing that even scarce vegetation can help shape where the birds interrupt their flights within the desert.

More interruptions occurred in the late afternoon

Flight interruptions were more concentrated during the late afternoon. The birds also showed a tendency to stop near locations that were subsequently used as night roosts. The authors interpret this pattern as active adjustment towards greener sites that can be used for afternoon foraging and as future night roosts.

A further seasonal difference emerged between the sexes. During autumn migration, females had shorter distances between stop sites than males, whereas no corresponding sex difference was found in spring. The authors suggest that shorter autumn intervals could reflect an energy-conserving strategy in the heavier females, but note that the absence of the same pattern in spring means this explanation remains uncertain. They therefore treat the result as a possible sex-specific difference in migration strategy that needs further study.

Wind conditions also affected interruption behaviour. The results therefore show that the short interruptions were associated not only with the sparse vegetation landscape but also with atmospheric conditions.

The study highlights the importance of scarce vegetated areas during trans-Saharan migration. Rather than treating the desert as a uniform barrier crossed without meaningful habitat use, the tracking data show that western marsh harriers make short-duration use of particular places within it. The authors argue that identifying these short-duration stop sites helps explain how the species manages migration through one of the most demanding sections of its flyway.

Sources and image credit

  1. Krejčí et al. — Flight Interruptions by European Western Marsh Harriers Crossing the Sahara Desert, Ardea 113(2)Primary peer-reviewed study. Although the Ardea issue and DOI carry a 2025 bibliographic designation, Crossref and the University of Almería publication record document first publication on 14 January 2026. GPS/GSM tracks from 2019–2023 showed selection of relatively greener stop sites during Sahara crossings, increased interruption density in late afternoon, a tendency to stop near subsequent night roosts, and effects of wind conditions.
  2. University of Almería research record — Flight Interruptions by European Western Marsh Harriers Crossing the Sahara DesertInstitutional publication record confirming the article date as 14 January 2026 despite the 2025 volume designation.

Image: Gidzy — wild male western marsh harrier in flight at Leighton Moss RSPB, England; Wikimedia Commons / Flickr; representative flight image, not one of the tracked birds · CC BY 2.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

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