Quantifying Bird Density During Migratory Stopover Using Weather Surveillance Radar

Estimating animal densities in the aerosphere using weather radar: To Z or not to Z?

“…Past efforts to quantify aerial densities based on radar observations have typically relied on comparing relative values of Z Kunz 2008, Buler andMoore 2011) or used linear regression to calibrate densities estimated from individual bioscatterers from marine radar to reported values of Z from NEXRAD installations (Diehl et al 2003, van Gasteren et al 2008, Buler and Diehl 2009. While these efforts have proved useful for answering ecological questions in certain contexts , Bonter et al 2009), they have limited generality and rely on the radar reflectivity factor, which assumes properties inherent to meteorological entities.…”

“…Clearly the number of animals in the aerosphere must decrease with height. Moreover, their distribution in height can vary depending on wind conditions, time of year, location, and so forth (Bruderer and Liechti 1998, Dolbeer 2006, Schmaljohan et al 2008, Buler and Diehl 2009. Therefore N bio should ideally be treated as a function of height.…”

“…Increased access to archived weather radar products has sparked interest in various biological uses of radar data (e.g., , Gauthreaux and Belser 1998, Diehl et al 2003, Horn and Kunz 2008, Buler and Diehl 2009. Advanced investigations that use these remotely sensed data to quantify population densities of animals in the aerosphere require a rigorous understanding of the basic mathematical properties and inherent assumptions in analyzing radar echo power.…”

Assessment of Bird Response to the Migratory Bird Habitat Initiative Using Weather-Surveillance Radar

“…For migrating land birds, their locations and relative densities for a given day are typically sampled using a single nearly instantaneous radar scan collected dur ing the abrupt en masse exodus of birds at evening civil twilight. Radar measures of reflectivity are strongly correlated with ground observations of bird densi ties and provide relative bird density measures that can be quantitatively com pared across the radar area after being adjusted for sampling biases (Buler and Diehl 2009). The evening en masse exo dus of wintering waterfowl between foraging and roosting habitats presents a similar opportunity to quantify bird dis tributions using weather surveillance radar observations.…”

“…Bias-adjusted radar reflectivity (i.e., the amount of radio energy returned by tar gets in the sampled airspace) measured at the onset of waterfowl evening feed ing flights was positively related to the observed diurnal density of radiomarked waterfowl locations at the ground. To improve the accuracy of re flectivity measures, the study team modified the algorithms of Buler and Diehl (2009) by interpolating reflectivity to a sun elevation angle of 5.0° below horizon (about 30 min after sunset). This time point occurs about 5 minutes after the mean onset of evening feeding flights and represented the sampling time point that optimized the correlation between radar and ground measures of bird density.…”