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Chiffchaff Subspecies Followed Different Migration Routes and Diverged Most Strongly at MARB

Common chiffchaff singing from a slender branch
Research · Genetics & genomics

Two subspecies of common chiffchaff (Phylloscopus collybita) around the Baltic Sea follow contrasting migration routes and show their strongest genomic differentiation in a repeat-rich region known as MARB, short for Migration Associated Repeat Block. The study, published on 9 July 2026, combined geolocator tracking, mitochondrial genotyping and whole-genome resequencing to examine how migration and genetic divergence are related in P. c. collybita and P. c. abietinus.

Light-level geolocators, which record day–night patterns that can be used to estimate a bird’s broad position during migration, were deployed on adult males in Sweden and Lithuania. Five usable tracks were recovered. Birds of the western collybita form migrated southwest and wintered on the Iberian Peninsula, whereas all three tracked abietinus reached East Africa near the Horn of Africa after taking a southeasterly route across the Mediterranean.

Two contact zones around the Baltic

The researchers also genotyped 196 chiffchaffs from populations around the Baltic Sea. The data confirmed contact zones between the two subspecies in south-central Sweden and in Poland. Despite their different migration directions, the two forms showed very low genome-wide differentiation, consistent with a relatively recent divergence and continued gene flow.

Demographic modelling placed the beginning of their divergence at roughly 100,000 years ago. Most of the strongest differentiation occurred on the Z chromosome and in MARB, while the autosomes were otherwise highly similar.

The same genomic region stands out in willow warblers

MARB is particularly notable because it is the only genomic region that stands out strongly in both migratory contrasts: between these chiffchaff subspecies and between willow warbler (Phylloscopus trochilus) subspecies that follow contrasting southwest and southeast routes. The authors therefore raise the possibility that MARB contributes to differences in migratory orientation in both species.

They do not conclude that MARB has been proven to control migration. The region contains many repetitive sequences and is difficult to resolve with short-read sequencing, so its detailed structure and variation remain uncertain. The precise mechanism linking MARB to migratory behaviour is still unknown.

The study shows that marked differences in migration can occur even between populations with little overall genomic differentiation. Finding the same unusual genomic region associated with migratory divides in both common chiffchaffs and willow warblers gives researchers a specific target for future work on how inherited migration programmes evolve.

Sources and image credit

  1. Caballero-Lopez, V., Mackintosh, A., Ekman, D., Proux-Wéra, E., Lundberg, M., Malmiga, G., Shipilina, D., Polakowski, M., Berdougo, M., Jankowiak, Ł., & Bensch, S. (2026). Common Chiffchaffs (Phylloscopus collybita) Diverge in a Genomic Region Associated With Migration Differences in Willow Warblers (Phylloscopus trochilus). Molecular Ecology, 35(13), e70462.

Image: Alexis Lours / Wikimedia Commons — live common chiffchaff, 24 May 2025; representative species image, not a tracked study bird · CC BY 4.0 · 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

Genetics & genomics

SPECIES IN THIS STORY

Species in this story

Common Chiffchaff Phylloscopus collybita Explore species Willow Warbler Phylloscopus trochilus Explore species

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