Detection range of songbirds using a stopover site by automated radio‐telemetry

Abstract

A major uncertainty in automated radio‐telemetry studies of small birds is the detection range 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.

Locating large insects using automated VHF radio telemetry with a multi‐antennae array

“…When the transmitter was attached to a mobile monarch butterfly, increased error in location estimates were expected due to interference of vegetation, variability in transmitter antenna orientation when in flight and height of the transmitter (Crewe et al., 2019; Kays et al., 2011; Ward et al., 2013). Estimated locations were a median of 58 m from their associated stationary location.…”

“…Estimated locations with the correction ranged in accuracy from 38 to 93 m and the pattern of estimated and actual locations were concordant. This approach assumes a constant vegetative effect; however, the impact of vegetation likely varies with plant height and density (Crewe et al., 2019; Kays et al., 2011; Ward et al., 2013). Further investigation could ascertain the need to use site‐specific vegetation to implement appropriate corrections for interference.…”

“…Our ARTS utilized a model that incorporated both power–distance and power–angle relationships. Performance of the ARTS was evaluated using a low‐powered, 0.22 g transmitter, taking into account factors including height and orientation of the transmitter, vegetation between the transmitter and the receiving station, and rate and pattern of transmitter movement (see Crewe et al., 2019; Kays et al., 2011; Lenske & Nocera, 2018; Ward et al., 2013).…”

“…Time sequences of power received during the observation period were smoothed using a gam() model, as described in Section 2.4.2. Because the vegetation present in the prairie restoration was expected to lower confidence in estimated location in comparison to the sod and harvested maize fields (Crewe et al., 2019; Goldman & Swenson, 1999; Kays et al., 2011; Larkin et al., 1996), we conducted a calibration test to quantify the distance–power relationship with the transmitter placed in a potted plant ( Chrysanthemum sp. ; Figure ).…”

“…Automated radio telemetry systems (ARTS) have been proposed as a means to increase scalability, frequency in data collection intervals and potentially minimize errors in location estimates for insects (Kissling et al., 2014). Several research teams have described ARTS for tracking mammals and birds (Cochran et al., 1965, 2001; Crewe et al., 2019; Kays et al., 2011; Knight et al., 2019; Larkin et al., 1996; Lenske & Nocera, 2018; Motus Wildlife Tracking System, 2020; Ward et al., 2013). Most notably Kays et al.…”