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Redwings Carried Ticks South on Their Late-Autumn Migration

Redwing standing on grass with its head and body clearly visible
Research: Disease, parasites & microbiology, Ecology

Even in November, redwings (Turdus iliacus) can carry many ticks on their journey south. In Belgium, researchers found ticks on 72.9% of 284 birds examined during autumn migration in 2024. A smaller survey at the same site in November 2022 found almost the same proportion: 72.2% of 108 birds carried ticks. Both autumns were unusually mild.

Redwings often search for food near the ground in woodland, forest edges and parks, where ticks can attach to them. A tick feeds for several days before dropping off. By then, its bird host may have travelled far, leaving the parasite in a different place.

Young birds carried more ticks

The castor bean tick (Ixodes ricinus) was the most common species and occurred only as larvae and nymphs. Adults primarily feed on medium-sized and large mammals. By contrast, the more bird-specialised Ixodes frontalis also included adult females feeding on the birds. Birds on their first autumn migration carried more ticks than older birds. The authors suggest that young birds may face greater exposure or have weaker acquired resistance.

Of 698 ticks screened for pathogens, 90, or 12.9%, contained Borrelia DNA. This bacterial group includes species that cause Lyme borreliosis in humans. No tick-borne encephalitis virus, which causes TBE, was detected.

The ticks contained several Borrelia species usually associated with birds, including B. garinii, as well as types primarily associated with mammals. Borrelia miyamotoi, which can cause relapsing fever, was found in ten ticks. Nearly a third of the birds carrying castor bean ticks and included in the pathogen analyses carried at least one Borrelia-infected tick.

This shows that the birds transported ticks containing bacterial DNA. The birds themselves were not tested for infection, and DNA detection alone does not establish whether all the bacterial types could be passed on to the tick’s next host.

Warmer autumns may give more ticks a ride

Many migrating birds use photoperiod, or day length, as a cue to leave. Ticks are ectothermic, relying on external heat, and their activity depends more strongly on temperature. When autumn stays mild, ticks can remain active as late-migrating thrushes pass through. The researchers suggest this may extend the period during which birds transport ticks and pathogens over long distances.

The potential scale is large. If the levels at the Belgian stopover applied throughout Europe, the authors calculated that redwings could have carried nearly 100 million infected ticks south in autumn 2024. That is an uncertain estimate from a single site, but it illustrates the potential role of an abundant migratory bird. Studies across more places and years are needed to establish how widespread the pattern is.

Sources and image credit

  1. Heylen, D. J. A., Ledegen, I., Grimon, M., Reteng, P., Hübschen, J. M., & Krawczyk, A. I. (2026). Lyme beyond the season: late-autumn dissemination of infected ticks by southward migrating redwings (Turdus iliacus). Parasites & Vectors, 19, 397.Primary peer-reviewed open-access article published 12 September 2026; full text checked. Ticks were found on 72.9% of 284 redwings captured during late-autumn migration in Belgium. Of 698 screened ticks, 12.9% were Borrelia-positive and none were positive for TBEV. The authors projected that redwings could have transported nearly 100 million infected ticks southward in autumn 2024, but explicitly caution that this extrapolation assumes one Belgian stopover was representative of the wider European migration.

Image: Redwing (Turdus iliacus) on Heligoland, Germany, 28 October 2012. Photo: Andreas Trepte / www.avi-fauna.info / Wikimedia Commons. CC BY-SA 2.5. Representative species image; not a bird from the Belgian tick study. · CC BY-SA 2.5 · Source

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