https://orcid.org/0000-0001-7009-9120
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Xu Shi, Jacob Drucker, Jason W Chapman, Melissa Sánchez Herrera, Adriaan M Dokter, Analysis of mixtures of birds and insects in weather radar profile data, Ornithological Applications, 2025;, duaf020, https://doi.org/10.1093/ornithapp/duaf020
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Abstract
Weather radars are increasingly used to study the spatial-temporal dynamics of airborne birds and insects. These two taxa often co-occur and separating their contributions is crucial for reliable interpretation of their movement patterns. Most studies have restricted analyses to locations, seasons, and periods in which one or the other taxa dominates. In this study, we describe an analytical method to estimate the proportion of birds and insects in cases where both taxa share the same airspace. Our approach partitions vertical profiles of biological reflectivity into bird and insect components, using assumptions of downwind heading selection by insects and information on expected airspeeds for birds and insects. We evaluated our method in regions, where existing approaches of studying bird migration with weather radars can be particularly challenging due to high airborne insect density: the tropics (Colombia) and the southern temperate zone (Southeast Australia). We found that bird and insect signals routinely reached similar magnitudes in these regions. Retrieved patterns of bird and insect occurrence across daily and annual cycles reflected expected biological patterns that are indicative of migratory and non-migratory movements in both climates and migration systems, particularly broad-front migration in birds. Contrary to fixed airspeed thresholding, we were able to partition birds along the full range of bird–insect proportions, retaining more spatial-temporal complexity that was crucial to revealing the aerial habitat use of both taxa. Our analytical procedure readily extends existing vertical profiling approaches, empowering ecologists to explore complex aerial ecosystems across a diverse range of climates, as well as potential diurnal movements of birds and insects that remain heavily understudied.
RESUMEN
Los radares meteorológicos se utilizan cada vez más para estudiar la dinámica espacio-temporal de aves e insectos en el aire. Estos dos taxones suelen presentarse en simultáneo, y separar sus contribuciones es crucial para una interpretación fiable de sus patrones de movimiento. La mayoría de los estudios han restringido sus análisis a ubicaciones, estaciones y períodos en los que uno de los dos taxones domina. En este estudio, describimos un método analítico para estimar la proporción de aves e insectos en casos en los que ambos taxones comparten el mismo espacio aéreo. Nuestro enfoque divide los perfiles verticales de reflectividad biológica en componentes de aves e insectos, utilizando suposiciones sobre la selección de rumbo a favor del viento por parte de los insectos e información sobre las velocidades aéreas esperadas para aves e insectos. Evaluamos nuestro método en regiones donde los enfoques actuales para estudiar la migración de aves con radares meteorológicos pueden resultar particularmente difíciles debido a la alta densidad de insectos en el aire: los trópicos (Colombia) y la zona templada del sur (sureste de Australia). Encontramos que las señales de aves e insectos alcanzaban magnitudes similares de manera rutinaria en estas regiones. Los patrones obtenidos de la presencia de aves e insectos a lo largo de los ciclos diarios y anuales reflejaron patrones biológicos esperados que son indicativos de movimientos migratorios y no migratorios en ambos climas y sistemas de migración, en particular la migración de frente amplio en las aves. A diferencia del umbral fijo de velocidad aérea, fuimos capaces de separar las aves en todo el rango de proporciones entre aves e insectos, manteniendo una mayor complejidad espacio-temporal, lo que fue crucial para revelar el uso del hábitat aéreo por parte de ambos taxones. Nuestro procedimiento analítico amplía fácilmente los enfoques actuales de perfilado vertical, facilitando a los ecólogos la exploración de ecosistemas aéreos complejos en una amplia variedad de climas, así como los posibles movimientos diurnos de aves e insectos, que siguen estando poco estudiados.
Lay Summary
• We developed a simple analytical method for partitioning bird and insect signals in weather radar data.
• The approach is based on minimal assumptions about the flight speeds and directions of birds and insects.
• We tested the method in regions with high insect density: the American tropics (Colombia) and southern temperate zone (Southeast Australia).
• After partitioning, we found bird and insect movements captured expected patterns of daily and annual movements, which were indicative of migratory and non-migratory movement of both taxa.
• Unlike fixed airspeed criteria for bird and insect separation, our approach provides a more detailed understanding of aerial habitat use by both birds and insects.
• The methodology is readily applied post-hoc to vertical profile retrievals and easily implemented in existing software packages, helping ecologists study bird and insect movements, where their separation in air space has previously proved challenging.
