The impact of radio-tags on Ruby-throated Hummingbirds (Archilochus colubris)

Radiotelemetry has advanced the field of wildlife biology, especially with the miniaturization of radio-tags. However, the major limitation when radio-tagging birds is the size of the animal to which a radio-tag can be attached. We tested how miniature radio-tags affected flight performance and behavior of Ruby-throated Hummingbirds (Archilochus colubris), possibly the smallest bird species that has been fitted with radio-tags. Using eyelash adhesive, we fitted hatch-year individuals (n = 20 males, n = 15 females) with faux radio-tags of 3 sizes that varied in mass and antenna length (220 mg, 12.7 cm; 240 mg, 12.7 cm; and 220 mg, 6.35 cm), then filmed the birds in a field aviary to quantify activity budgets. We also estimated flight range using flight simulation models. When the 3 radio-tag packages were pooled for analysis, the presence of a radio-tag significantly decreased both flight time (similar to 8%) and modeled flight range (similar to 23%) in comparison to control birds. However, a multiple-comparison analysis between the different packages revealed that there was a significant difference in flight time when the larger radio-tag package (240 mg) was attached, and no significant difference in flight time when the lighter radio-tag packages (220 mg) were attached. Our results are similar to those of other studies that analyzed the flight time or flight range of birds wearing radio-tags. Therefore, currently available lightweight radio-tags (<= 220 mg) may be a new option to aid in the study of hummingbird biology. Future study should focus on the additional drag created by the radio-tag and the effects of the lightest radio-tag packages on free-ranging birds. These studies would provide additional information to determine the feasibility of the use of radio-tags to study hummingbird biology.