Data and code from: Variable evidence of radio-tag backpacks affecting hummingbird time budgets in captivity

Background: 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.

Methods: 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.

Results: 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. 

Conclusions: 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.

Methods
As described above, we performed enclosure-style experiments (n = 25) consisting of two randomized treatments, tagged and untagged, to characterize and quantitatively compare behavior of Black-throated Mangoes when equipped (or not) with radio-transmitter backpack harnesses. Each treatment included a 30-minute acclimation period and a subsequent 60-minute observation period, in which we filmed the hummingbird's behavior. As such, we generated 50 one-hour videos throughout this study, which we analyzed using the Behavioral Observation Research Interactive Software (BORIS). With BORIS, we created time-budget breakdowns of our behaviors of interest: flying, hover-feeding, preening, and perching. 

In this dataset you can find our time budget breakdowns for each individual treatment for each bird. Also included are additional covariates that we considered relevant to hummingbird behavior: treatment type (2 levels: tagged and untagged); individual’s weight at the start of the trial (continuous, in grams); treatment number (2 levels: treatment 1 and treatment 2); tent’s average internal temperature for the treatment (continuous, in Celsius); percent sucrose** of the provided nectar throughout the trial (continuous); and period of day wherein the majority of the treatment took place (3 levels: morning, 6:00–11:59; afternoon, 12:00–15:59; and early evening, 16:00–on). These data are included in one master dataframe.

Furthermore, you can find an inter-rater reliability dataframe, which we used to determine the reliability of our ethological video analyses and the protocols with which we differentiated behavior types. These data comprise 24 measurements (6 raters scoring the same 4 videos). We used these data to compare raters’ calculated durations (of flying, hover-feeding, preening, and perching) for the subset of videos in a single statistical test.

Lastly, you can find two smaller dataframes in this dataset: one which includes the full amount of time each bird was tested in our aviary-style "entanglement tests" overnight (n = 6), and another which breaks down the weight specifications of all the birds we tested, the radio-telemeters they wore in the experiment, the harness used to equip the radio-telemeters, and the passive integrated transponders that we tagged individuals with prior to beginning this study.

We also include all code used to conduct our analyses.