Climate, spatial, and demographic predictors of avian malaria parasite infection in Marsh Tits

Abstract

Parasites play a fundamental role in explaining variation in population dynamics in wild ecosystems while also acting as a better model-system to study similar or related human infections. Since the late 1800s, malaria parasites have played a crucial role in vector-borne disease research. Many intrinsic and environmental factors can affect the level of infection transmission and prevalence among avian host populations. Importantly, climate change, being a multifaceted phenomenon, is expected to increase vector-borne infections, not just through temperature changes, but through changes in other environmental dynamics. Empirically proving this effect has so far been hindered by the lack of proper long-term studies.

A population of breeding marsh tits (Poecile palustris) has been monitored in a long-term study, spanning 17 years, at two nest box areas in Revinge and Öved. Making this marsh tit population a good opportunity to investigate the effects of different intrinsic and ecological drivers of avian malaria. Additionally, a blue tit (Cyanistes caeruleus) population occupying the same study sites has been monitored for malaria parasites during the same period. Making it an optimal “sister” model-system for infection prevalence comparisons.

Using these long-term data, prevalence of three haemosporidian genera (Haemoproteus, Plasmodium, and Leucocytozoon) was analyzed in relation to host sex, location, temperature, and breeding phenology. Prevalence was similar between both sexes except for Leucocytozoon, where male hosts had a significantly higher level of infection. Spatially, Revinge had significantly higher prevalence for Haemoproteus, Plasmodium while Öved had significantly higher prevalence of Leucocytozoon. Yearly values showcased Haemoproteus had a quadratic relationship with lower prevalence in earlier and later years, while Plasmodium had linearly increasing prevalence. Leucocytozoon prevalence remained somewhat similar through the study period. Maximum temperature significantly influenced Haemoproteus and Plasmodium prevalence, while having no clear association with Leucocytozoon. Hatch dates did not significantly influence any prevalence, except that of Leucocytozoon. Prevalence in marsh tits was consistently lower than in blue tits, although both species exhibited similar temporal trends, with significant positive correlations in prevalence across years.


These findings suggest environmental and intrinsic drivers affect the prevalence of the three parasite genera in different ways. While differences in prevalence between species may reflect variation in host encounter rates and compatibility with the parasite. The results highlight the importance of considering both environmental and host-specific factors in multi-host parasite systems.

Popular Abstract

What Drives Malaria Infections in Marsh Tits?

Parasites play an important role in nature by helping shape wild populations. They can also help researchers better understand similar or related human diseases, making them a very valuable model system. Among the different types, avian malaria parasites have been central in parasite research. Many factors can affect the level of infection in birds. Of these factors, climate change and global warming are expected to increase infection rates. This does not only happen through temperature changes, but also through other environmental changes like precipitation and seasonal patterns. Understanding these effects have not been properly studies as they require long-term studies, that are still rare.

A long-term study of marsh tits in southern Sweden, has offered a unique chance to investigate the drivers of malaria infections in the wild birds. Over 17 years, researchers have monitored the population in two different sites while collecting blood samples from the individuals. What also makes this study very valuable is that the same site is shared by a population of blue tits. Comparing the infection level in both bird species can help us better understand why one might carry more infections than the other.

Marsh Tit Infections
Using this long-term data, the study explored how sex, location, climate and breeding time can influence the level of malaria infections in the marsh tits. The study looked at three different types of malaria parasites, and the infection patterns between them were different. Male and female marsh tits were very similar in infection rates, except for one parasite type were males had a higher risk of being infected with it. Infection rates of all malaria types differed between the two study locations. Two parasite groups were affected by temperature, becoming more or less common under different thermal conditions, while a third showed little response to change in climate. Breeding time did not affect the infection rates of two malaria types, while it did affect the third type.


Blue Tit vs. Marsh Tit
When blue tit and marsh tit were compared, marsh tits had consistently lower infections. Interestingly, the pattern of yearly change in infection was very similar between both species. This suggests that although the two species might be different in how sensitive they are to malaria, or how many times they might encounter it, they still respond to environmental drivers in a similar way.


Overall, this study shows that to understand how specific malaria infections work in the wild, both environmental factors and traits of the infected animals must be taken into consideration. Moreover, the study highlights the dangers of climate change and how it might reshape how different parasites can spread in the future.


Master’s Degree Project in Biology, 45 credits, 2026
Advisors: Jan-Åke Nilsson and Olof Hellgren
Department of Biology, Lund University.

• author: El Bayoumy, Youssef
• supervisor: Olof Hellgren; Jan-Åke Nilsson
• organization: Degree Projects in Biology
• course: BION02 20252
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9226030
• date added to LUP: 2026-05-08 11:17:38
• date last changed: 2026-05-08 11:17:38