Effects of harness-attached tracking devices on survival, migration, and reproduction in three species of migratory waterfowl

Background Tracking devices have enabled researchers to study unique aspects of behavior in birds. However, it has become clear that attaching these devices to birds often affects their survival and behavior. While most studies only focus on negative effects on return rates, tracking devices can also affect the behavior under study, and it is therefore important to measure potential negative effects of tracking device attachment on the full range of behavioral aspects of birds. At the same time, we should aim to improve our current attachment methods to reduce these effects. Results We used a modified harness to attach tracking devices to a total of 111 individuals of three goose species (Greater White-fronted Geese, Brent Geese, and Barnacle Geese) to study their migratory behavior. By creating control groups of birds marked with colored leg bands, geolocators, and/or neck collars, we were able to compare return rates, body condition, and migratory and reproductive behavior, thus allowing a much broader comparison than return rates alone. Birds with harness-attached tracking devices had lower return rates, which could partly be explained by increased rates of divorce, but is likely also the result of reduced survival induced by the harness and device. A comparison between Barnacle Geese equipped with harness-attached tracking devices and individuals fitted with geolocators attached to leg bands showed that birds equipped with tracking devices were only slightly delayed in timing of migration and reproduction and otherwise were not affected in reproductive output. Conclusions We argue that tracking devices can be used for studies on migration timing. Nevertheless, given the effect of tracking devices on survival and divorce rate, which may differ between sexes and species, we stress that researchers should carefully consider which birds to tag in order to reduce potential negative effects.