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Eurasian Blue Tits and Great Tits Showed Different Plumage Shifts Along Polish Urban Gradients

Eurasian blue tit showing yellow breast and blue crown, wing and tail
Research · Ecology

Urbanisation was associated with different changes in plumage colour in Eurasian blue tits (Cyanistes caeruleus) and great tits (Parus major), according to a study published on 19 March 2026. Researchers sampled 309 birds along eight replicated urban–rural gradients across Poland and measured carotenoid-based, structural and melanin-based feather colours.

The sample included 108 blue tits and 201 great tits. Urbanisation was quantified using the proportion of impervious surfaces and tree cover around the sampling sites, allowing the researchers to compare birds across mosaics ranging from forested to strongly built-up habitats.

Blue tit breast and tail brightness shifted in opposite directions

In blue tits, the brightness of the yellow breast plumage decreased with increasing urbanisation. Structural colour on the tail showed the opposite pattern: tail brightness increased in more urbanised habitats. Importantly, breast carotenoid chroma — a measure more directly linked to how much carotenoid pigment is deposited in the feathers — did not decline. Blue tits therefore did not show the classic “urban dullness” pattern seen when carotenoid colour itself becomes less saturated.

The authors suggest that the contrasting responses reflect different underlying processes. The increase in blue-tit tail brightness ran opposite to what would be expected if urban dust simply accumulated on structurally coloured feathers and reduced their reflectance. They therefore suggest that effective preening, differences in feather wear or changes in feather quality may contribute to the pattern.

Great tits showed a different urban colour pattern

Great tits responded differently even though they occupied the same urban gradients. Their breast carotenoid chroma decreased as urbanisation increased, consistent with the urban-dullness pattern, and variation among individuals in this trait increased toward more urban habitats. The study found no corresponding urbanisation effect on the measured melanin-based traits of great tits.

The researchers interpret the lower carotenoid chroma in urban great tits as potentially linked to reduced dietary carotenoid availability and physiological stress. They also report the increased variation in this colour trait as the first such urban pattern documented for avian plumage. Greater environmental heterogeneity within cities may help generate that variation, which could in turn alter the strength or direction of selection on the trait.

Sources and image credit

  1. Janas, K., Chatelain, M., Corsini, M., Da Silva, A., Wardecki, Ł., Szulc, J., & Szulkin, M. (2026). Replicated urban mosaics reveal trait- and species-specific shifts in carotenoid and structural plumage colouration of two passerines. Scientific Reports, 16, 14132. https://doi.org/10.1038/s41598-026-44382-yPrimary peer-reviewed study, first published 19 March 2026. Sampled 309 Eurasian blue tits and great tits across eight replicated urban–rural gradients in Poland.

Image: Tim Sträter — Eurasian blue tit; Wikimedia Commons / Flickr; representative species image, not a bird from the Polish study · CC BY 2.0 · Source

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Ecology

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Eurasian Blue Tit Cyanistes caeruleus Explore species Great Tit Parus major Explore species

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