Research disturbance negatively impacts incubation behaviour of female great tits

Abstract

Human-induced disturbance is perceived by avian species as a predation risk. However, the anti-predatory behaviour triggered by these non-lethal events can have negative impacts on reproduction and offspring survival. Research on breeding birds often involves visits to their nests and is likely to disrupt parental behaviour, but nest visits that do not involve direct handling of females have been overlooked as important disturbance events. This study focuses on the impacts of short visits to the nest of incubating Great tit (Parus major) females. We investigated how long they stay away from the nest (off-bout) after a disturbance, their possible compensatory behaviour once they resume incubation (on-bout), and the effects on daily incubation rhythms. We used three years of data from two breeding populations to assess the consequences of disturbances in two scenarios: when the female is present in the nest and flushed, and when the female is absent. We found that after a disturbance, the immediate off-bout was longer when the female was either present or absent, with the magnitude of the disturbance being greater when females were flushed. Females did not compensate with longer on-bouts afterwards, i.e. the research disturbance altered daily incubation behaviour by reducing the total time spent on the nest in relation to the number of daily disturbance events. Females that alter their behaviour in response to perceived predation risk would perform longer incubation periods, resulting in lower hatching rates. These effects of research on female behaviour should be considered when planning field experiments.

Significance statement

Incubating birds react to human activity near their nests by changing their behaviour. This may also apply to basic research activities, but we have no data on how a visit, e.g., to check clutch size, affects them. To find out, we classified data from routine research visits to great tit nests, which are often used for research in the wild, into long and short visits. We also considered whether a female was incubating or foraging outside the nest during the visit. We found that females tended to stay away from the nest longer after they encounter a researcher, and after longer visits. Our results show that even slight research activities in the nest alters female incubation behaviour. They flee and leave the clutch unattended for longer, changing the thermal environment of the nest, which is crucial for proper embryo development.