How do cranes meet their needs in complex environments?

Tracking data has revealed the remarkable migrations undertaken by cranes, with some migratory routes covering more than 6,400 kilometers round trip. 

These journeys involved overcoming substantial natural barriers, such as the Alps, the Himalayas, the deserts of the Arabian Peninsula, and the Mediterranean Sea. 

Monitoring the movement of cranes 

Researchers used miniature GPS tracking devices to monitor the movements of 104 cranes across Africa, Asia, and Europe. These devices featured unique solar-powered GPS leg bands, developed by scientists from the Max Planck Institute of Animal Behavior (MPI-AB). 

In addition to the tracking data, the researchers developed a statistical framework to analyze how the cranes’ movements were influenced by environmental factors, such as the presence of crops, water bodies, temperature, and vegetation cover.

“Animals have to satisfy their own needs with what they can get from their environment, but both of these are changing constantly,” said lead author Scott Yanco, a postdoctoral researcher at the University of Michigan. 

“This creates an intriguing optimization problem that we wanted to know if cranes were solving through long-distance migration.”

Environmental challenges faced by cranes 

The study found that all four crane species faced vastly different environmental conditions throughout the year, and that these conditions were synchronized with key life events. 

The stark contrasts in temperature or resource availability between their wintering grounds and summer breeding grounds were particularly notable. 

For some cranes, the migrations themselves involved drastic shifts in environmental conditions. For instance, the demoiselle cranes had to contend with significant temperature fluctuations as they migrated across the Tibetan plateau.

“We suspect this all has to do with different biological needs during these different times of the year,” added Yanco, who conducted the research while at the Yale Center for Biodiversity and Global Change. 

Finding areas with abundant resources 

Yanco pointed out that common cranes clearly prioritized agricultural areas during the late summer, a time that aligns with raising juveniles and preparing for fall migration. 

“This is exactly when we would expect them to want easy access to food,” Yanco explained.

For other species, accessing food came with trade-offs. The black-necked cranes, for example, had to balance between safe roosting habitats and areas with abundant resources. 

The competing needs of cranes

“Amazingly, the balance between these competing needs changed over the year depending on what the birds were doing,” Yanco said. During migration, they chose safer roosting sites, while during breeding, they prioritized abundant food sources.

“This type of shifting emphasis depending on what cranes need at any given time is what we were expecting to see,” said senior author Ivan Pokrovsky, a postdoctoral researcher at MPI-AB. 

“But we were blown away by how well the cranes used movement to resolve trade-offs among competing needs and to access certain environments during key periods of the year.”

Wildlife conservation efforts

Understanding how animals interact with their environment not only offers a more nuanced view of how they survive in complex ecosystems but is also essential for informing conservation and management strategies in the face of the twin crises of climate change and biodiversity loss. 

The study’s framework provides a statistical tool to better understand the intricate relationships between animals and their environments, which can be widely applied to wildlife conservation efforts.

“When we know how animals use certain environmental conditions, we can make better predictions about how species might respond to human-caused global change and develop more effective interventions that ensure we preserve the conditions species need to survive,” Pokrovsky concluded.

More about cranes

Cranes are highly social and often travel in large flocks during migration. They are also vocal birds, using a variety of calls that can be heard from miles away, which helps them communicate with other members of their flock. 

Cranes are omnivores, feeding on a diverse diet that includes plants, seeds, small animals, and insects. Some species of cranes are endangered, largely due to habitat loss and environmental changes. 

For example, the Siberian crane is critically endangered. Ongoing conservation efforts aim to protect its breeding grounds in Russia and wintering habitats in China and India.

Cranes have deep cultural significance in many parts of the world. In Japan and China, they are symbols of longevity, peace, and good fortune, and they are prominently featured in folklore and art. 

The whooping crane, native to North America, is a symbol of conservation success, having recovered from the brink of extinction due to extensive preservation efforts.

The study is published in the Proceedings of the National Academy of Sciences.

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