Skip to content

Leucocytozoon Infection Probability Rose From About 20% to 60% in Later-hatching Eurasian Blue Tit Chicks

Juvenile Blue Tit (Cyanistes caeruleus) perched on a branch
Research · Disease, parasites & microbiology

Eurasian blue tit (Cyanistes caeruleus) nestlings that hatched later in spring were much more likely to carry Leucocytozoon blood parasites than early-hatching chicks, according to a Scottish study published on 10 February 2026. The probability of infection rose from around 20% early in the season to around 60% later in spring, and this pattern was independent of whether the birds lived in urban or forest habitat.

Leucocytozoon are haemosporidian blood parasites that cause a form of avian malaria and are transmitted mainly by blackflies. Infections can range from little visible effect to severe disease, so the timing of exposure may matter for nestling condition and survival.

The researchers followed Eurasian blue tits at three forest sites around Loch Lomond and two urban sites in Glasgow over four breeding seasons from 2016 to 2019. They sampled three to four 13-day-old nestlings per nest and screened 320 birds with a newly developed quantitative PCR assay that could distinguish and quantify Leucocytozoon and Haemoproteus.

Almost one-third carried Leucocytozoon

Leucocytozoon was detected in 32.5% of the nestlings. In contrast, only six birds, 1.8%, were infected with Haemoproteus, and no consistent urban–forest difference emerged for Leucocytozoon. Hatch date stood out clearly: later-hatching nestlings had a higher probability of infection in both habitats.

The authors suggest that early-hatching chicks may overlap less with the seasonal emergence of the insects that transmit Leucocytozoon. Because both bird breeding and vector emergence vary with environmental conditions, differences in timing may help explain why previous studies have found inconsistent relationships between urbanization and avian malaria.

Heavy infections were linked to lower body mass

Most infected nestlings carried low parasite loads. Among the 11 heavily infected birds, all from forest sites, birds with higher infection intensity had lower body mass. Across all infected nestlings, however, infection intensity was not detectably related to body mass, and across the full dataset Leucocytozoon prevalence did not explain fledging success.

The study also found that urban nestlings had a lower probability of fledging than forest nestlings, but this difference was not explained by Leucocytozoon infection. The authors therefore distinguish the parasite pattern from the broader urban–forest difference in fledging success.

Sources and image credit

  1. Dominoni, D. M., Albalawi, B. F. A., Mladenova, M., Helm, B., & Baldini, F. (2026). Phenology underlies inconsistent urbanization effects on avian malaria (Leucocytozoon sp.) in juvenile songbirds. Ecosphere, 17(2), e70545. https://doi.org/10.1002/ecs2.70545Primary peer-reviewed open-access article, first published and version of record online 10 February 2026 under CC BY 4.0. The study screened 320 blue tit nestlings from three forest and two urban sites in Scotland across four breeding seasons.

Image: Dave Howes / Wikimedia Commons — juvenile blue tit (Cyanistes caeruleus) in Norfolk, England, photographed 23 May 2011. Representative juvenile photograph, not a bird from the Scottish study. Cropped to 16:9 for the news-card format. · CC BY-SA 2.0 — https://creativecommons.org/licenses/by-sa/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

Disease, parasites & microbiology

SPECIES IN THIS STORY

Species in this story

Eurasian Blue Tit Cyanistes caeruleus Explore species

Independent research and conservation news archive

Did you find this information useful?

Wildlife Vagabond is independently built and maintained. Voluntary support helps cover source verification, hosting and continued work on research and conservation news.

Support Wildlife Vagabond

The news archive will remain freely available.