Authors: Tara L. Crewe, Jessica E. Deakin, Andrew T. Beauchamp, and Yolanda E. Morbey
Publication: Journal of Field Ornithology
Publication link: https://doi.org/10.1111/jofo.12291
Keywords: automated radio-telemetry, ecological methods, manual radio-telemetry, migratory stopover habitat, sampling design
Abstract: A major uncertainty in automated radio-telemetry studies of small birds is the detectionrange of receiving antennas. We compared simultaneous daytime detections ( 30 s) by automated and manual radio-telemetry to assess detection probability and the proportion of transmissions detected for birds
on migratory stopover as a function of distance, foraging guild (Black-throated Blue Warblers, Setophaga caerulescens, and Yellow-rumped Warblers, Dendroica coronata coronata, represented mid-canopy foliage gleaners and White-throated Sparrows, Zonotrichia albicollis, represented a ground forager), habitat type, meteorological variables, tower antenna number (1–4), and the position of a bird relative to the receiving antenna’s bearing (offset angle). Our study was conducted at a migratory stopover site in southern Ontario, Canada. Most detections were in dense to sparse forest, and all individuals were within 1.03 km of the automated receiving station. Daily detection probability was near 100% for both foraging guilds. However,within 30 s before and after a manual radio-telemetry location was made, detection probability and the proportion of transmissions detected by automated radio-telemetry declined with distance, was higher for warblers than sparrows, and was lowest for 90° offset angles. Our results suggest that when research goals do not require detections with high temporal frequency, e.g., estimation of departure date or daily departure probability, our study design had an effective detection range of at least 1 km. However, where temporal precision is required, e.g., to investigate movements and changes in activity levels during stopover, detection range was ~300 m for ground-foraging sparrows and 600 m for mid-canopy foraging warblers, which is much lower than the presumed detection range of antennas under optimal conditions (15 km). This corresponds to a spatial area of coverage for forest-dwelling birds of ~0.3–1.1 km2. Our results suggest that to optimally configure an automated radio-telemetry array at the regional scale, investigators should carefully consider detection range and its underlying covariates, including species type, the habitat matrix, and the orientation of antennas relative to preferred habitat.