Over the course of three years (2019, 2021, and 2022), the team determined the sex of the bitten birds by analyzing blood from the abdomens of vector insects captured in the nests. In 2021, males were bitten more often than females, coinciding with a year when males weighed less than in other years. Furthermore, during the final year of the study, researchers used molecular tools and DNA genotyping to identify the specific chicks bitten by each insect. They analyzed the DNA from both the blood ingested by the insects and the birds in the nest.

“These analyses revealed that the most bitten chicks were lighter-weight males positioned closer to the nest entrance. This may be because insects prefer individuals in poorer physical condition, as their defenses are weaker, or because hungrier chicks, seeking food, move closer to the nest entrance, making them more exposed to bites,” explains Marina García del Río, a researcher at the National Museum of Natural Sciences.

The results, published in the journal Molecular Ecology, shed light on how vector insects select their hosts, offering insights into the transmission of infectious diseases such as avian malaria. “Understanding the differences in infection rates between males and females in wildlife can help help us understand the implications for studies on mosquito bites in humans. Previous research has shown that certain factors, such as blood type, influence the likelihood of being bitten,” adds García del Río.

The study also involved researchers from the Complutense University of Madrid (UCM), the University of Alcalá, and the Biomedical Research Networking Center (CIBER).