Combining radio-telemetry and radar measurements to test optimal foraging in an aerial insectivore bird

Abstract

Optimal foraging theory posits that foragers adjust their movements based on prey abundance to optimize food intake. While extensively studied in terrestrial and marine environments, aerial foraging has remained relatively unexplored due to technological limitations. This study, uniquely combining BirdScan-MR1 radar and the ATLAS biotelemetry system, investigates the foraging dynamics of Little Swifts ( Apus affinis ) in response to insect movements over Israel’s Hula Valley. Insect Movement Traffic Rate (MTR) substantially varied across days, strongly influencing swift movement. On days with high insect MTR, swifts exhibited reduced flight distance, increased colony visit rate, and earlier arrivals at the breeding colony, reflecting a dynamic response to prey availability. However, no significant effects were observed in total flight duration, speed, or daily route length. Notably, as insect abundance increased, inter- individual distances decreased. These findings suggest that Little Swifts optimize their foraging behavior in relation to aerial insect abundance, likely influencing reproductive success and population dynamics. The integration of radar technology and biotelemetry systems provides a unique perspective on the interactions between aerial insectivores and their prey, contributing to a comprehensive understanding of optimal foraging strategies in diverse environments.