Variable evidence of radio-tag backpacks affecting hummingbird time budgets in captivity

With wildlife-tracking devices miniaturizing rapidly to enable ever-more research on ever-smaller taxa, there is a newfound urgency for affordable, field-accessible biologging ethics studies. We designed a 3-hour time-budget experiment to investigate how radio-transmitter backpacks affect hummingbirds’ behavior in Colombia. Using a large flight arena, we individually filmed 25 Black-throated Mangoes (Anthracothorax nigricollis) under two randomized treatments, tagged and untagged, to characterize and quantitatively compare behavior. We created time-budget breakdowns of our behaviors of interest—flying, hover-feeding, preening, and perching—then fit a series of linear mixed-effects models to determine the effects of tagging and additional experimental and environmental variables on behavior. We also designed an aviary-style “Entanglement Experiment” (n = 30) to determine if any individuals would snag on vegetation while equipped with the backpack harness, and tested 6 additional birds in this enclosure overnight for any longer-term negative effects. When tagged, individuals on average spent overall less time flying (with fewer and shorter bouts); and more total time feeding, preening (with more and longer bouts in both cases), and perching (with fewer but longer bouts)—however, this difference in total duration was only statistically significant in the case of preening. Our best-supported models also highlighted the importance of the following additional effects: whether or not the bird was undergoing its first or second 1.5-hour treatment (birds flew significantly more in their second treatment), bird mass (lighter birds fed significantly longer overall), and the time of day (birds preened significantly more in the afternoon than the morning, and more in the evening than the afternoon). No individuals in this captive study became entangled in vegetation or exhibited any adverse overnight effects from harness wear. In our captive study, radio-transmitter backpacks significantly affected the amount of time that hummingbirds spent preening, and additional environmental variables helped explain behavioral differences in each bird’s treatments. While being in a confined space doubtlessly affected the behavior of individuals, our experimental model is relatively straightforward to fine-tune to other small avian taxa and is suitable for remote conditions, providing a useful basis for examining species-specific effects of biologging prior to starting field studies.