Data from: Great tits do not compensate over time for a radio-tag-induced reduction in escape-flight performance

Mizumo Tomotani, Barbara; Muijres, Florian T.; Johnston, Bronwyn; Jeugd, Henk P. van der; Naguib, Marc


The use of biologging and tracking devices is widespread in avian behavioural and ecological studies. Carrying these devices rarely has major behavioural or fitness effects in the wild, yet it may still impact animals in more subtle ways, such as during high power demanding escape manoeuvres. Here, we tested whether or not great tits (Parus major) carrying a backpack radio-tag changed their body-mass or flight behaviour over time to compensate for the detrimental effect of carrying a tag. We tested 18 great tits, randomly assigned to a control (untagged) or one of two different types of a radio-tag as used in previous studies in the wild (0.9 g or 1.2 g; ~5% or ~6–7% of body mass, respectively), and determined their upward escape-flight performance 1, 7, 14, and 28 days-after-tagging. In between experiments, birds were housed in large free-flight aviaries. For each escape-flight, we used high-speed 3D videography to determine flight paths, escape-flight-speed, wingbeat frequency and actuator-disk-loading (ratio between the bird weight and aerodynamic thrust production capacity). Tagged birds flew upwards with lower escape-flight speeds, caused by an increased actuator-disk-loading. During the 28-day period, all groups slightly increased their body mass and their in-flight wingbeat frequency. In addition, during this period all groups of birds increased their escape-flight speed, but tagged birds did so at a lower rate than untagged birds. This suggests that birds may increase their escape flight performance through skill-learning, however, tagged birds still remained slower than controls. Our findings suggest that tagging a songbird can have a prolonged effect on the performance of rapid flight manoeuvres. Given the absence of tag-effects on reproduction and survival in most songbird radio-tagging studies, tagged birds in the wild might adjust their risk-taking behaviour to avoid performing rapid flight manoeuvres.