Tiny radio-tag backpacks impact, but do not significantly affect, hummingbird time budgets in captivity

BackgroundGiven that wildlife tags have recently become miniaturized enough to work with some of the worlds smallest vertebrates, 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. Using a large flight arena in Colombia, we individually filmed 25 Black-throated Mangoes (Anthracothorax nigricollis) under two randomized treatments, tagged and untagged, to characterize and quantitatively compare their behavior. We analyzed all videos using the Behavioral Observation Research Interactive Software (BORIS), to create time-budget breakdowns of our key behaviors of interest: flying, feeding, preening, and perching. We also designed an aviary-style "entanglement test" (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. ResultsAcross duration, number of bouts, and bout length, we found no significant differences in the behavior of individuals (flying, feeding, preening, and perching) when they were or were not tagged. However, the additive effects of treatment number (whether the bird was undergoing its first or second 1.5-hour treatment) and treatment type (tagged or untagged) most accurately predicted time spent flying (birds flew significantly more in their second 1.5-hour treatment). The weight of the bird, meanwhile, best predicted feeding duration (lighter birds fed significantly more). Lastly, the additive effects of time of day and treatment type had the highest predictive accuracy of time spent preening (birds preened significantly more in the afternoon than the morning, and significantly more in the evening than the afternoon); here, the effect of treatment type was highly significant. In our aviary tests, no individuals became entangled in vegetation or exhibited any adverse overnight effects from harness wear. ConclusionsIn our captive study, radio-transmitter backpacks did not significantly affect hummingbird behavior when considered independently; however, additional covariates are essential to account for, and the effects of being in a confined space may also be significant. Nonetheless, our experimental model is relatively straightforward to fine-tune to other small taxa and is suitable for remote conditions, providing a useful basis with which to examine species-specific effects of biologging prior to starting field studies.