Tracking data has revealed the incredible migrations of cranes, with some routes spanning more than 6,400 kilometers round trip.
These journeys involved overcoming great natural barriers such as the Alps, the Himalayas, the deserts of the Arabian Peninsula and the Mediterranean Sea.
Monitor the movement of the crane
The researchers monitored the movements of 104 cranes across Africa, Asia and Europe using small GPS tracking devices equipped with unique solar-powered GPS leg bands developed by scientists at the Max Planck Institute for Animal Behaviour (MPI-AB).
In addition to the tracking data, the researchers developed a statistical framework to analyze how environmental factors such as the presence of crops, water bodies, temperature and vegetation cover affect crane movements.
“Animals have to satisfy their needs with what they get from their environment, and both are constantly changing,” said lead author Scott Janko, a postdoctoral researcher at the University of Michigan.
“This creates an interesting optimization problem, and we wanted to know whether cranes are solving it throughout their long-distance migration.”
Environmental issues facing cranes
The study found that all four crane species face very different environmental conditions throughout the year, and that these conditions are synchronized with important life events.
The striking differences in temperature and resource availability between wintering and summer breeding grounds were particularly striking.
For some cranes, the migration itself involves dramatic changes in environmental conditions: Demoiselle cranes, for example, have had to cope with significant temperature fluctuations as they crossed the Tibetan Plateau.
“We suspect this all has to do with different biological needs at different times of the year,” added Janko, who conducted the research at Yale University’s Center for Biodiversity and Global Change.
Find resource-rich areas
Yanko noted that the cranes clearly prioritize farmland because late summer coincides with the time when they are rearing their young and preparing for autumn migration.
“This is the exact time they’ll want easy access to food,” Yanko explained.
For other species, obtaining food involves trade-offs: Black-necked Cranes, for example, must strike a balance between safe roosting habitat and areas rich in resources.
Competing Needs for Cranes
“Surprisingly, the balance of these competing needs shifted throughout the year depending on the birds’ behavior,” Janko says. During migration, birds chose safer roosting sites, and during breeding season they prioritized abundant food sources.
“We expected that the emphasis would shift depending on what the cranes needed at any given time,” said Ivan Pokrovsky, a postdoctoral researcher at MPI-AB and lead author of the paper.
“But we were amazed at how the cranes cleverly used movement to resolve trade-offs between competing needs and access specific environments at key times of the year.”
Wildlife Conservation
Understanding how animals interact with their environments not only gives us a more nuanced view of how they survive in complex ecosystems, but is also essential for developing conservation and management strategies in the face of the twin threats of climate change and biodiversity loss.
This research framework provides a statistical tool to better understand the complex relationships between animals and their environments and has broad applications in wildlife conservation efforts.
“By understanding how animals exploit specific environmental conditions, we can better predict how species will respond to human-induced global change and develop more effective interventions to ensure that the conditions necessary for species’ survival are maintained,” Pokrovsky concluded.
More about cranes
Cranes are highly social birds that often travel in large flocks during migration, and they are noisy birds that communicate with other members of their flock using a variety of calls that can be heard from miles away.
Cranes are omnivorous and feed on a wide variety of plants, seeds, small animals and insects. Several species of cranes are in danger of extinction, mainly due to habitat loss and environmental changes.
For example, the Siberian crane is critically endangered, and ongoing conservation efforts aim to protect its breeding grounds in Russia and its wintering grounds in China and India.
Cranes have deep cultural significance in many parts of the world: in Japan and China, cranes are symbols of longevity, peace and good fortune and often feature in folklore and art.
Native to North America, the whooping crane is a conservation success story, having been brought back from the brink of extinction through intensive conservation efforts.
The research is published in the Proceedings of the National Academy of Sciences.
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