Droevendaalsesteeg 10
6708 PB Wageningen
The Netherlands
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About
My research focusses on vector borne diseases in bird populations to investigate which birds are impacted by these diseases and detect the underlying mechanism of these effects. My project includes an in-depth study on Common blackbirds.
Biography
I started in 2016 with the study Applied Biology at the HAS Hogeschool, which was followed by the Master Biology at the Radboud University in Nijmegen. During my masters I worked on modelling population dynamics and effects of environmental conditions on the populations of Oystercatchers, Kentish and Ringed plovers.
Publications
Peer-reviewed publications
Silent reservoir species are shaping the emergence of Usutu virus
https://doi.org/10.1038/s41559-025-02973-4Disentangling the contributions of different hosts to disease transmission is highly complex but critical for improving predictions, surveillance and response. This is particularly challenging in wildlife, with pathogens often infecting multiple species and data collection being difficult. Using the emergence of Usutu virus (USUV) in the Netherlands as a case study, we demonstrate the use of an approximate Bayesian computation framework on diverse data sources to uncover drivers of spatiotemporal wildlife disease emergence. We calibrated single- and multi-host mechanistic transmission models to five types of wildlife surveillance and research data, describing molecular and serological evidence of USUV in birds. Although Eurasian blackbirds, the primary target species for surveillance, were most severely affected, our models indicated that USUV could not persist in blackbirds alone. Our framework provided statistical support for additional, unobserved bird species to have contributed to transmission. This population of bird species is characterized by limited infection mortality, a longer lifespan and likely further dispersal than blackbirds. Immunity in this population appears to have protected blackbirds from further USUV-related population decline. Our results underscore the importance of considering multiple host populations to understand outbreak dynamics. Neglecting the multi-host context of transmission can impact the reliability of predictions and projected impact of interventions.
Urbanization is associated with innate immune functions in adult, but not nestling Turdus merula (Eurasian Blackbird)
Increasing urbanization poses significant risks to organisms confronted with new and rapidly changing environments. Long-term exposure to urban environments may involve changes in the immune system and its interrelated processes. A properly functioning immune system is essential for health maintenance, including the prevention of infection, so identifying and understanding the links between urbanization and immunological changes can offer insights into wildlife health and disease emergence. Here, we investigated the relationship between three measures of innate immune defenses in nestling and adult Turdus merula (Eurasian Blackbird) and the level of urbanization. Two of these immune defenses were positively correlated with urbanization in adults, but no relationships were found between urbanization and immune defenses in nestlings. Additionally, no apparent trade-offs between body condition and immune defenses measures were observed. Our results suggest that urbanization does not negatively impact immune defenses in T. merula, but immune defenses may be upregulated in adult birds to cope with the environmental stressors related to urban habitats. Our study highlights the complexity of immune regulation in heterogeneous environments, such as urban environments, and emphasizes the need for more empirical research to disentangle how specific ecological pressures shape immune function across life stages.https://doi.org/10.1093/ornithapp/duaf056From Mosquitoes to Birds
This thesis examines how vector-borne pathogens (VBPs) are emerging and spreading in increasingly urbanized environments, and how these changes affect wild bird populations. Early detection and surveillance are shown to be essential for managing risks to wildlife, domestic animals, and humans. Using public reports of dead birds, chapter 2 demonstrates that citizen-science data can effectively track pathogen emergence. The mosquito-borne virus USUV spread rapidly across the Netherlands, moving from the southeast to the north within three years and causing a 30% decline in Blackbird populations. Such data proved valuable for modelling transmission dynamics and linking pathogen pressure to wildlife population declines. Chapter 3 extends these findings by showing that other resident or short-distance migratory species, Song Thrush, Dunnock, Eurasian Wren, and Eurasian Robin, also experienced population declines associated with USUV. Long-distance migrants were unaffected, suggesting they play a limited role in year-round VBP transmission. Chapters 4 and 5 explore why resident birds may be key contributors to pathogen maintenance. Movement analyses revealed substantial spatial mixing: juveniles dispersed widely, while adults frequently moved between urban and non-urban habitats, likely tracking seasonal resources. These movements can expose urban populations to new pathogens and shape local transmission patterns. Finally, the thesis investigates how urban environments affect host immunity. Adult Blackbirds showed altered immune profiles in urban areas, potentially reflecting upregulated defences in response to urban stressors. No such patterns were found in nestlings, and no trade-offs between body condition and immunity were detected. Overall, this work highlights how urbanization, bird movement, and immune responses interact to influence VBP transmission. It underscores the importance of continued surveillance and offers insights for both public health and avian conservation.
Popular-scientific publications
Trekvogels geven inzicht in verspreiding infectieziekten
Wilde trekvogels spelen een belangrijke rol bij de introductie en verspreiding van infectieziekten die van dier op mens worden overgedragen, Los van de oorsprong van infectieziekten, kan onderzoek aan trekvogels dan ook belangrijke lessen leren over de verspreiding van die infectieziekten.Broedresultaten van Merels in het bos en in stedelijk gebied - leefgebieden met afwijkende populatietrends
After a long period of increase, the Dutch breedingpopulation of the Blackbird stabilized from the 1990s onwards, with large variation between habitats. Particularly in urban areas, and in woodlands in the northern part of the country, the numbers have declined markedly. Since reproductive data are scarce, we collected data on breeding performance in 2021 and 2022 as part of the ‘Year of the Blackbird’. In these years 361 respectively 535 nest records were submitted by dedicated volunteers, far more than the average of 83 per year in 1995-2020. Blackbirds started egg-laying in urban areas earlier than in woodland habitat (Fig. 2), and seem to have advanced egg-laying by a week since 1990. On average 3.4 young fledged per successful nest, without clear differences between habitats or time periods. On average 26.1% of Blackbird nests were successful. Nest success was higher in urban areas than in woodlands, but also declined stronger over time (Fig. 3). Within urban areas, the number of fledged young per successful nest decreased with increasing urbanisation (Fig. 4), but not nest success. Within woodlands, nest success was lower in the northern part of the country, where population abundance decreased, as compared to other parts. Gathering data on reproduction and survival from other nationwide surveys is necessary to assess the relative importance of these demographic drivers for the recent Blackbird decline.Vis als voedsel voor nestjongen bij Merels
On May 20th in 2022 we observed that a breeding pair of the Common Blackbird fed Three-spined Sticklebacks Gasterosteus aculeatus to their 5-days-old chicks twice. In 2016 an online video showed another Blackbird feeding its 9-day-old chicks with Sticklebacks in the Netherlands. To understand whether catching fish (and possibly feeding fish to nestlings) is perhaps more common among passerines, we sent out a nationwide call to report observations of fishing passerines and searched the scientific literature and online media for reports of this phenomenon. We received nine observations of fishing Common Blackbirds, and five observations of fishing by three other non-corvid passerine bird species. This suggests that capturing and feeding fish seems a rare but widespread behaviour among passerines. Blackbirds normally rely on earthworms and caterpillars to feed their chicks, however, 2022 was one of the driest years in the Netherlands. Drought and heat may have resulted in lower availability of earthworms and caterpillars, while chances of finding fish in shallow or dried-up streams would be relatively high. As a result, some Blackbirds may have substituted the low availability of earthworms and caterpillars with fish to feed their nestlings. Fish has a lower calorific value in gram dry mass than earthworms and caterpillars, but it has a higher content of lipids and consists of 10% less water compared to earthworms. Fish feeding may thus be profitable when other food sources become scarce, such as during severe droughts. However, more observations are needed to understand whether fish feeding is a novel behaviour driven by the more frequent occurrence of droughts or a common behaviour among passerines breeding near water.
Projects & collaborations
Projects
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One Health PACT - Predicting Arboviruses Climate Tipping points
Our water-dominated landscape, combined with a dense human- and livestock population make the Netherlands particularly vulnerable to outbreaks of zoonotic viral diseases that are transmitted by mosquitoes among avian and mammalian host species.
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PhD thesis defence Jurrian van Irsel: From mosquitoes to birds
Jurrian van Irsel will defend his PhD thesis, titled "From mosquitoes to birds: Unravelling the role of avian hosts in vector-borne pathogen dynamics".