Rush or relax: migration tactics of a nocturnal insectivore in response to ecological barriers

Author(s): Lathouwers, M., Artois, T., Dendoncker, N., Beenaerts, N., Conway, G., Henderson, I., Kowalczyk, C., Davaasuren, B., Bayargur, S., Shewring. M., Cross, T., Ulenaers, E., Liechti, F. & Evens, R.

Published: March 2022 Pages: 10pp

Journal: Scientific Reports Volume: 12 ( part 4964 )

Digital Identifier No. (DOI): 10.1038/s41598-022-09106-y

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New research involving BTO has confirmed the theory the migratory birds use different strategies at different points on their migratory journeys, speeding up when passing through inhospitable regions and slowing down where conditions are more favourable. Using GPS and data loggers, researchers tracked Nightjars breeding in the UK, Belgium and Mongolia as they travelled to their wintering grounds. Birds were found to adopt a 'rush' tactic when passing through ecological barriers, such as the Saharan and Arabian Deserts. This tactic involved a high daily travel speed and flight altitude, and a high migration probability at dusk and at night. By contrast, in semi-open, hospitable habitats, birds travelled at lower speeds and had a lower migration probability at dusk. The likely reflected birds slowing down to forage and refuel before the rest of their journey.

Abstract

During their annual migration, avian migrants alternate stopover periods, for refuelling, with migratory flight bouts. We hypothesise that European Nightjars (Caprimulgus europaeus) adapt their daily migration tactics in association with biomes. We tracked the autumn migration of 24 European Nightjars, from breeding populations in Mongolia, Belgium and UK, using GPS-loggers and multisensor data loggers. We quantified crepuscular and nocturnal migration and foraging probabilities, as well as daily travel speed and flight altitude during active migration in response to biomes. Nightjars adopt a rush tactic, reflected in high daily travel speed, flight altitude and high migration probabilities at dusk and at night, when travelling through ecological barriers. Migration is slower in semi-open, hospitable biomes. This is reflected in high foraging probabilities at dusk, lower daily travel speed and lower migration probabilities at dusk. Our study shows how nightjars switch migration tactics during autumn migration, and suggest nightjars alternate between feeding and short migratory flight bouts within the same night when travelling through suitable habitats. How this may affect individuals’ fuel stores and whether different biomes provide refuelling opportunities en route remains to be investigated, to understand how future land-use change may affect migration patterns and survival probabilities.

Notes

The BTO authors wish to acknowledge the help and financial support received from Mark Constantine, Forestry England, and the British Birds Charitable Trust.

Staff Author(s)