title: Flight modes in migrating European bee-eaters: heart rate may indicate low metabolic rate during soaring and gliding.
abstract: BACKGROUND
  Many avian species soar and glide over land. Evidence from large birds (m(b)>0.9 kg) suggests that soaring-gliding is considerably cheaper in terms of energy than flapping flight, and costs about two to three times the basal metabolic rate (BMR). Yet, soaring-gliding is considered unfavorable for small birds because migration speed in small birds during soaring-gliding is believed to be lower than that of flapping flight. Nevertheless, several small bird species routinely soar and glide.
  
  
  RESULTS
  To estimate the energetic cost of soaring-gliding flight in small birds, we measured heart beat frequencies of free-ranging migrating European bee-eaters (Merops apiaster, m(b)∼55 g) using radio telemetry, and established the relationship between heart beat frequency and metabolic rate (by indirect calorimetry) in the laboratory. Heart beat frequency during sustained soaring-gliding was 2.2 to 2.5 times lower than during flapping flight, but similar to, and not significantly different from, that measured in resting birds. We estimated that soaring-gliding metabolic rate of European bee-eaters is about twice their basal metabolic rate (BMR), which is similar to the value estimated in the black-browed albatross Thalassarche (previously Diomedea) melanophrys, m(b)∼4 kg). We found that soaring-gliding migration speed is not significantly different from flapping migration speed.
  
  
  CONCLUSIONS
  We found no evidence that soaring-gliding speed is slower than flapping flight in bee-eaters, contradicting earlier estimates that implied a migration speed penalty for using soaring-gliding rather than flapping flight. Moreover, we suggest that small birds soar and glide during migration, breeding, dispersal, and other stages in their annual cycle because it may entail a low energy cost of transport. We propose that the energy cost of soaring-gliding may be proportional to BMR regardless of bird size, as theoretically deduced by earlier studies.
authors.affiliation: Movement Ecology Laboratory, Department of Evolution, Systematics and Ecology, Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Nir
authors.initials: N
authors.lastname: Sapir
authors.forename: Martin
authors.initials: M
authors.lastname: Wikelski
authors.forename: Marshall D
authors.initials: MD
authors.lastname: McCue
authors.forename: Berry
authors.initials: B
authors.lastname: Pinshow
authors.forename: Ran
authors.initials: R
authors.lastname: Nathan
mesh_terms: D025041:Animal Migration / Q000502:physiology; D000818:Animals; D001481:Basal Metabolism / Q000502:physiology*; D001717:Birds / Q000502:physiology*; D005426:Flight, Animal / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D012044:Regression Analysis; D013686:Telemetry; D014921:Wings, Animal / Q000502:physiology