Extreme altitude changes between night and day during marathon flights of great snipes

Abstract

Several factors affect the flight altitude of migratory birds, such as topography, ambient temperature, wind conditions, air humidity, predation avoidance, landmark orientation, and avoiding over-heating from direct sunlight.1Alerstam T. Bird Migration. Cambrige University Press, 1990Google Scholar, 2Liechti F. Schaller E. The use of low-level jets by migrating birds.Naturwissenschaften. 1999; 86: 549-551Crossref PubMed Scopus (49) Google Scholar, 3Shamoun-Baranes J. Liechti F. Vansteelant W.M.G. Atmospheric conditions create freeways, detours and tailbacks for migrating birds.J. Comp. Physiol. A Neuroethol. Sens. Neural Behav. Physiol. 2017; 203: 509-529Crossref PubMed Scopus (69) Google Scholar, 4Senner N.R. Stager M. Verhoeven M.A. Cheviron Z.A. Piersma T. Bouten W. High-altitude shorebird migration in the absence of topographical barriers: avoiding high air temperatures and searching for profitable winds.Proc. Biol. 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Unexplained altitude changes in a migrating thrush: long-flight altitude data from radio-telemetry.Auk. 2015; 132: 808-816Crossref Scopus (25) Google Scholar The reasons behind these altitude changes are not well understood. In their seasonal migrations between Sweden and sub-Saharan Africa, great snipes Gallinago media make non-stop flights of 4,000–7,000 km, lasting 60–90 h.9Klaassen R.H.G. Alerstam T. Carlsson P. Fox J.W. Lindström A. Great flights by great snipes: long and fast non-stop migration over benign habitats.Biol. Lett. 2011; 7: 833-835Crossref PubMed Scopus (89) Google Scholar,10Lindström Å. Alerstam T. Bahlenberg P. Ekblom R. Fox J.W. Råghall J. Klaassen R.H.G. The migration of the great snipe Gallinago media: intriguing variations on a grand theme.J. Avian Biol. 2016; 47: 321-334Crossref Scopus (23) Google Scholar Activity and air pressure data from multisensor dataloggers showed that great snipes repeatedly changed altitudes around dawn and dusk, between average cruising heights about 2,000 m (above sea level) at night and around 4,000 m during daytime. Frequency and autocorrelation analyses corroborated a conspicuous diel cycle in flight altitude. Most birds regularly flew at 6,000 m and one bird reached 8,700 m, possibly the highest altitude ever recorded for an identified migrating bird. The diel altitude changes took place independently of climate zone, topography, and habitat overflown. Ambient temperature, wind condition, and humidity have no important diel variation at the high altitudes chosen by great snipes. Instead, improved view for orientation by landmarks, predator avoidance, and not least, seeking cold altitudes at day to counteract heating from direct sunlight are the most plausible explanations for the diel altitude cycle. Together with similar recent findings for a small songbird,6Sjöberg S. Malmiga G. Nord A. Andersson A. Bäckman J. Tarka M. Willemoes M. Thorup K. Hansson B. Alerstam T. Hasselquist D. Extreme altitudes during diurnal flights in a nocturnal songbird migrant.Science. 2021; 372: 646-648Crossref PubMed Scopus (4) Google Scholar the great snipes’ altitudinal performance sheds new light on the complexity and challenges of migratory flights.

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