Elting, R. | Search bioRxiv

bioRxiv2025

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.

animal behavior and cognition↗

bioRxiv2024

PicoCam: High-resolution 3D imaging of live animals and preserved specimens

1. The PicoCam system is a multi-camera photogrammetry rig used for generating high-resolution 3D models of animals in the field, or preserved specimens in laboratory or museum settings. The digital measurement of 3D models is increasingly useful for studying body shape. However, methods that capture sub-millimetric detail often do so at the cost of portability and versatility; this system aims to bridge this gap. 2. The PicoCam system employs 3D digital photogrammetry, a process that generates accurate, full-color, 3D models from sequences of photographs. By using six cameras and a rotating base, the system is able to capture multiple angles in rapid succession - a key advantage for both 3D-imaging live specimens and efficiently scanning museum specimens. Through the use of macro lenses and high-resolution camera sensors, this system can capture sub-millimetric detail without sacrificing portability. 3. In this study, we 3D imaged the bills of 19 species of hummingbirds using the PicoCam system and measured length, height, width, surface area, and volume of their bills. We examined eight species in the field and 11 from the Burke Museum in Seattle. We chose Hummingbird bills as a model system, as their fine-scale interspecific differences in 3D shape can have significant functional and behavioral implications, and could tell us more about how these traits predict habitat and resource use. 4. The prospect of a common 3D-imaging method for both museum and field use is compelling when documenting structures shape within and among species. The PicoCam system is also valuable for quantifying the 3D shape of fine-scale phenotypes (like hummingbird bills) that benefit from digital measurement, preservation, and improved accessibility. Lastly, the PicoCam system allows "digital 3D collection", by which the shape of biological structures in the field can be recorded and stored in a public database without the need to collect a specimen. This opens the door to studies in which multiple 3D image captures of the same individual across different time scales permit 3D shape/color comparisons (e.g., seasonal, ontogenetic changes).

evolutionary biology↗