Research disturbance negatively impacts incubation behaviour of female Great Tits

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 imply visiting their nests and likely disrupt parental behaviour, but nest visits where females are not directly handled have previously 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 (longer on-bouts), and the effects on daily incubation rhythms. We used three years of data from two breeding populations to assess the consequences of disturbance in two scenarios: when the female is present in the nest and flushed out, and when the female is absent. We found that following a disturbance, the immediate off-bout was longer, both when the female was present and absent, with the magnitude of the disturbance being greater when females were flushed. The females did not compensate by longer on-bouts afterwards, therefore research disturbance altered daily incubation behaviour by decreasing the total time spent on the nest as a function of the number of daily disturbance events. Females that alter their behaviour in response to the perception of predation risk would perform longer incubation periods that result in lower hatching rates. These effects of research on female behaviour should be considered when planning field experiments.