Batbayar Galtbalt1, Amanda Lilleyman2, Jonathan T Coleman3, Chuyu Cheng4, Zhijun Ma4, Danny I Rogers5,6, Bradley K Woodworth7, Richard A Fuller7, Stephen T Garnett2, Marcel Klaassen8,9. 1. Centre for Integrative Ecology, School of Life and Environmental Science, Deakin University, Geelong, Victoria, Australia. batbr19@gmail.com. 2. Threatened Species Recovery Hub, National Environment Science Program, Research Institute for Environment and Livelihoods, Charles Darwin University, Ellengowan Drive, Casuarina, Northern Territory, 0909, Australia. 3. Queensland Wader Study Group, 22 Parker Street, Shailer Park, 4128, Australia. 4. Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Coastal Ecosystems Research Station of the Yangtze River Estuary, Institute of Biodiversity Science, School of Life Sciences, Fudan University, Shanghai, 200433, China. 5. Department of Environment, Water, Land and Planning, Arthur Rylah Institute, PO Box 137, Heidelberg, Victoria, 3084, Australia. 6. Australasian Wader Studies Group, Melbourne, Victoria, Australia. 7. School of Biological Sciences, University of Queensland, Brisbane, Queensland, Australia. 8. Centre for Integrative Ecology, School of Life and Environmental Science, Deakin University, Geelong, Victoria, Australia. 9. Victorian Wader Study Group, Melbourne, Victoria, Australia.
Abstract
BACKGROUND: In-flight conditions are hypothesized to influence the timing and success of long-distance migration. Wind assistance and thermal uplift are thought to reduce the energetic costs of flight, humidity, air pressure and temperature may affect the migrants' water balance, and clouds may impede navigation. Recent advances in animal-borne long-distance tracking enable evaluating the importance of these factors in determining animals' flight altitude. METHODS: Here we determine the effects of wind, humidity, temperature, cloud cover, and altitude (as proxy for climbing costs and air pressure) on flight altitude selection of two long-distance migratory shorebirds, far eastern curlew (Numenius madagascariensis) and whimbrel (Numenius phaeopus). To reveal the predominant drivers of flight altitude selection during migration we compared the atmospheric conditions at the altitude the birds were found flying with conditions elsewhere in the air column using conditional logistic mixed effect models. RESULTS: Our results demonstrate that despite occasional high-altitude migrations (up to 5550 m above ground level), our study species typically forego flying at high altitudes, limiting climbing costs and potentially alleviating water loss and facilitating navigation. While mainly preferring migrating at low altitude, notably in combination with low air temperature, the birds also preferred flying with wind support to likely reduce flight costs. They avoided clouds, perhaps to help navigation or to reduce the risks from adverse weather. CONCLUSIONS: We conclude that the primary determinant of avian migrant's flight altitude selection is a preference for low altitude, with wind support as an important secondary factor. Our approach and findings can assist in predicting climate change effects on migration and in mitigating bird strikes with air traffic, wind farms, power lines, and other human-made structures.
BACKGROUND: In-flight conditions are hypothesized to influence the timing and success of long-distance migration. Wind assistance and thermal uplift are thought to reduce the energetic costs of flight, humidity, air pressure and temperature may affect the migrants' water balance, and clouds may impede navigation. Recent advances in animal-borne long-distance tracking enable evaluating the importance of these factors in determining animals' flight altitude. METHODS: Here we determine the effects of wind, humidity, temperature, cloud cover, and altitude (as proxy for climbing costs and air pressure) on flight altitude selection of two long-distance migratory shorebirds, far eastern curlew (Numenius madagascariensis) and whimbrel (Numenius phaeopus). To reveal the predominant drivers of flight altitude selection during migration we compared the atmospheric conditions at the altitude the birds were found flying with conditions elsewhere in the air column using conditional logistic mixed effect models. RESULTS: Our results demonstrate that despite occasional high-altitude migrations (up to 5550 m above ground level), our study species typically forego flying at high altitudes, limiting climbing costs and potentially alleviating water loss and facilitating navigation. While mainly preferring migrating at low altitude, notably in combination with low air temperature, the birds also preferred flying with wind support to likely reduce flight costs. They avoided clouds, perhaps to help navigation or to reduce the risks from adverse weather. CONCLUSIONS: We conclude that the primary determinant of avian migrant's flight altitude selection is a preference for low altitude, with wind support as an important secondary factor. Our approach and findings can assist in predicting climate change effects on migration and in mitigating bird strikes with air traffic, wind farms, power lines, and other human-made structures.
Entities:
Keywords:
Air temperature; Altitude selection; Atmospheric condition; Migration; Shorebird; Weather
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