Effects of experimental nest treatment with herbs on ectoparasites and body condition of nestlings

Nest fumigation behavior involves the incorporation of fresh green plant fragments that contain ectoparasite-repellent volatile compounds into birds' nests. This behavior is relatively rare among bird species, and there is ongoing debate about whether it benefits parental breeding success. In this study, we experimentally tested whether the inclusion of aromatic-herbal plant fragments in the nests of great tits affects the physiological condition of nestlings, as indicated by blood levels of hematocrit, hemoglobin, glucose, and body condition indices, such as weight and wing length. We divided the nests into 2 groups, adding aromatic herbs to the test group's nests and non-aromatic plants to the control group. After the nestlings fledged, all nest materials were collected to extract, identify, and count arthropod ectoparasites. Nestlings in nests supplemented with aromatic plant fragments had elevated levels of hematocrit and hemoglobin, indicating improved physiological condition compared to the control group. Ectoparasites were present in both groups, although ticks (Ixodidae) occurred less frequently in nests with aromatic plants. The experimental treatment did not affect fledging success. Further experimental studies are needed to explore the effects of incorporating aromatic plant fragments into tit nests within the frameworks of both the nest protection hypothesis and the drug hypothesis.