Foraging at the edge of the world: Low-altitude, high-speed maneuvering in barn swallows

Douglas R. Warrick, Tyson L. Hedrick, Andrew A. Biewener, Kristen E. Crandell, Bret W. Tobalske

Research output: Contribution to journalArticlepeer-review

Abstract

While prior studies of swallow manoeuvering have focused on slow-speed flight and obstacle avoidance in still air, swallows survive by foraging at high speeds in windy environments. Recent advances in field-portable, high-speed video systems, coupled with precise anemometry, permit measures of high-speed aerial performance of birds in a natural state. We undertook the present study to test: (i) the manner in which barn swallows (Hirundo rustica) may exploit wind dynamics and ground effect while foraging and (ii) the relative importance of flapping versus gliding for accomplishing high-speed manoeuvers. Using multi-camera videography synchronized with wind-velocity measurements, we tracked coursing manoeuvers in pursuit of prey. Wind speed averaged 1.3–2.0 m s21 across the atmospheric boundary layer, exhibiting a shear gradient greater than expected, with instantaneous speeds of 0.02–6.1 m s21. While barn swallows tended to flap throughout turns, they exhibited reduced wingbeat frequency, relying on glides and partial bounds during maximal manoeuvers. Further, the birds capitalized on the near-earth wind speed gradient to gain kinetic and potential energy during both flapping and gliding turns; providing evidence that such behaviour is not limited to large, fixed-wing soaring seabirds and that exploitation of wind gradients bysmall aerial insectivores may be a significant aspect of their aeroecology.

Original languageEnglish
Article number20150391
JournalPhilosophical Transactions of the Royal Society B: Biological Sciences
Volume371
Issue number1704
DOIs
StatePublished - Sep 26 2016

Keywords

  • Flapping
  • Foraging flight
  • Gliding
  • Kinematics
  • Wind energy

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