How cheap is soaring flight in raptors? A preliminary investigation in freely-flying vultures.
Measuring the costs of soaring, gliding and flapping flight in raptors is challenging, but essential for understanding their ecology. Among raptors, vultures are scavengers that have evolved highly efficient soaring-gliding flight techniques to minimize energy costs to find unpredictable food resources. Using electrocardiogram, GPS and accelerometer bio-loggers, we report the heart rate (HR) of captive griffon vultures (Gyps fulvus and G. himalayensis) trained for freely-flying. HR increased three-fold at take-off (characterized by prolonged flapping flight) and landing (>300 beats-per-minute, (bpm)) compared to baseline levels (80-100 bpm). However, within 10 minutes after the initial flapping phase, HR in soaring/gliding flight dropped to values similar to baseline levels, i.e. slightly lower than theoretically expected. However, the extremely rapid decrease in HR was unexpected, when compared with other marine gliders, such as albatrosses. Weather conditions influenced flight performance and HR was noticeably higher during cloudy compared to sunny conditions when prolonged soaring flight is made easier by thermal ascending air currents. Soaring as a cheap locomotory mode is a crucial adaptation for vultures who spend so long on the wing for wide-ranging movements to find food.
Centre d'Ecologie Fonctionnelle et Evolutive (UMR5175), Université Montpellier 2, Biogeography and Ecology of Vertebrates, Montpellier, France ; Université Pierre et Marie Curie, UMR7204 CERSP, Muséum National d'Histoire Naturelle, Paris, France.
Olivier
O
Duriez
Université de Strasbourg, IPHC, Strasbourg, France ; CNRS, UMR7178, Strasbourg, France.
Akiko
A
Kato
Centre d'Ecologie Fonctionnelle et Evolutive (UMR5175), Université Montpellier 2, Biogeography and Ecology of Vertebrates, Montpellier, France ; Université de Strasbourg, IPHC, Strasbourg, France.
Clara
C
Tromp
Ornis italica, Rome, Italy.
Giacomo
G
Dell'Omo
Institute of Neuroinformatics, University of Zurich/ETH Zurich, Zurich, Switzerland.
Alexei L
AL
Vyssotski
Université Pierre et Marie Curie, UMR7204 CERSP, Muséum National d'Histoire Naturelle, Paris, France.
François
F
Sarrazin
Université de Strasbourg, IPHC, Strasbourg, France ; CNRS, UMR7178, Strasbourg, France.
Yan
Y
Ropert-Coudert
D000818:Animals; D005426:Flight, Animal; D006339:Heart Rate; D020304:Raptors / Q000502:physiology*