Fine-scale changes in speed and altitude suggest protean movements in homing pigeon flights.

Baptiste Garde,Anders Hedenström,Martin Wikelski,Steven J Portugal,Emily L C Shepard,Emmanouil Lempidakis,Michael Quetting,Giacomo Dell'Omo,Luca Börger,Rory P Wilson

doi:10.1098/rsos.210130

Abstract

The power curve provides a basis for predicting adjustments that animals make in flight speed, for example in relation to wind, distance, habitat foraging quality and objective. However, relatively few studies have examined how animals respond to the landscape below them, which could affect speed and power allocation through modifications in climb rate and perceived predation risk. We equipped homing pigeons (Columba livia) with high-frequency loggers to examine how flight speed, and hence effort, varies in relation to topography and land cover. Pigeons showed mixed evidence for an energy-saving strategy, as they minimized climb rates by starting their ascent ahead of hills, but selected rapid speeds in their ascents. Birds did not modify their speed substantially in relation to land cover, but used higher speeds during descending flight, highlighting the importance of considering the rate of change in altitude before estimating power use from speed. Finally, we document an unexpected variability in speed and altitude over fine scales; a source of substantial energetic inefficiency. We suggest this may be a form of protean behaviour adopted to reduce predation risk when flocking is not an option, and that such a strategy could be widespread.

Highlights

Time and energy are currencies that have a profound influence on animal movement, with the judicious use of energy being pertinent for flying animals, due to the scale of the costs in flapping flight [1,2]
No differences in individual wing loading were observed between the two field seasons and neither was there a significant difference in the average airspeed recorded for each pigeon
Homing pigeons have been bred for their ability to return to the loft quickly, and the selective pressure to minimize the flight time is likely to outweigh that to minimize power

Summary

Introduction

Time and energy are currencies that have a profound influence on animal movement, with the judicious use of energy being pertinent for flying animals, due to the scale of the costs in flapping flight [1,2]. [13,22], though see [9,23]) This means that factors impacting the choice of flight speed over fine scales, including changes in the substrate (mainly land cover and topography) that birds fly over, tend to be averaged out. We quantified variation in speed in relation to land cover, predicting that an increase in speed or altitude above a certain type of land cover is likely to represent a response to greater perceived predation risk Overall, this should provide insight into the fine-scale changes in effort and perceived risk driven by the landscape that could influence the costs associated with route choice when a flight is considered in all three dimensions. A visual representation of the GPS tracks was generated using the R package ‘ggmap’ [47]

Results

Discussion

61. Garde B et al 2021 Data from