Radiotagged fledgling Savannah Sparrows Passerculus sandwichensis at risk of entanglement in vegetation.

Radiotelemetry is an essential method for studying the movements and survival of cryptic grassland bird fledglings. There is mixed evidence on the effects of wearing radio‐transmitters for passerines, with negative consequences probably under‐reported. In one season of a 2‐year study, we found 23% of radio‐transmitters and/or antennas deployed on fledgling Savannah Sparrows Passerculus sandwichensis had become entangled in vegetation, consequently harming the fledglings in two of seven cases. It is important for researchers to share their information on any negative consequences of attaching radio‐transmitters to songbirds in order to improve methods and to harm fewer individuals in future studies. [ABSTRACT FROM AUTHOR]