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

Radio telemetry has advanced the field of wildlife biology, especially with the miniaturization of radio-tags. However, the major limitation faced with 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 to be fitted with radio-tags. Using eyelash adhesive, we fitted hatch year individuals (n=20 males and 15 females) with faux radio-tags of three sizes varying in mass and antenna length (220mg-12.7cm, 240mg-12.7cm, and 220mg-6.35cm), then filmed the birds in a field aviary to quantify activity budgets. We also estimated flight range using flight simulation models. When the three radio-tag packages were pooled for analysis, the presence of a radio-tag significantly decreased both flight time (-8%) and modeled flight range (-23%) when compared 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 (240mg) was attached and no significant difference in flight time when the lighter radio-tag packages (220mg) were attached. Our results are similar to other studies which analyzed the flight time or flight range of birds wearing radio-tags. Therefore, currently available light weight radio-tags (≤220mg) may be a new option to aid in the study of hummingbird biology. Future study should focus upon 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 on the use of radio-tags to study hummingbird biology. Keywords: radio transmitters, radio telemetry, Ruby-throated Hummingbirds, Archilochus colubris, radio-tagging, behavior, flight simulations, migration

A cautionary tale: surrogates for radio-tagging practice do not always simulate the responses of closely related species

Telemetry is useful for monitoring rare and threatened species if they can be effectively tagged. Relatively abundant, closely related species are sometimes used as surrogates in refining tagging methods or testing the suitability of methods before transfer to rare and threatened species. A decision framework for developing a radio-tagging method of an endangered fish (Macquaria australasica; Percichthyidae) is presented based on experiences with tagging a closely related, surrogate species (Macquaria ambigua). Aquaria and field-based trials demonstrated the suitability of internally implanting a radio-tag with an externally exited antenna on the surrogate species. However, transferring this method to the endangered species under field conditions was unsuccessful in terms of mortality and/or radio-tag rejection. In this case, a surrogate species served to refine radio-tagging methods, but did not successfully indicate the suitability of these methods for a closely related species. This cautionary tale illustrates that surrogate species are not always effective and extrapolation of methods, even across closely related species, may be perilous.

Radio-tagging and tracking of translocated trout cod (Maccullochella macquariensis: Percichthyidae) in an upland river

Radio-tracking provides an effective means of studying the spatial ecology of threatened fishes where almost inaccessible habitats and species rarity render conventional mark–recapture methods impractical. Initially, validation of an effective radio-tagging method is required; in the present study, an aquaria trial based on nine hatchery-reared, adult male Maccullochella maquariensis (Percichthyidae) was conducted. Fish resumed feeding within days of being internally implanted with a radio-tag, and tag rejection was not observed (0%, n = 9) based on a 2-month observational period. Following release into an upland stream, individual-specific movements resulted in upstream (n = 1) and downstream (n = 6) dispersal as well as fidelity to the release site (n = 2) at the completion of the study. Individuals established small home-ranges (mean length of river used by an individual per diel period ranged from 47 to 292 m) and were most active in the early morning and evening (n = 6). Complete survivorship of individuals bearing active radio-transmitters (n = 8) was recorded up until 4 months after release. However, an estimated zero or one individual was alive when the last active radio-tag expired 11 months after release (n = 8). The present study highlights the use of radio-tracking in monitoring the dispersal and survivorship of small numbers of hatchery-reared threatened fish released into natural habitats as part of species re-introduction programs.