Migratory mule deer do not need instructions: study

How do big gameers know where to migrate year after year over hundreds of kilometers of Wyoming's vast landscapes?

Among scientists, there are two camps of thought. The first is that animals use local signals in their neighborhood to determine where to migrate. Animals can climb in areas where forage is greener (often called green wave surfing) or descend from mountains with thicker snow. The second idea is that animals develop the memory of the landscape in which they live and then use this information to guide their movements.

Recent research from the University of Wyoming has shown that memory largely explains the behavior of deer during their migration: mule deer navigate in spring and fall, primarily using their knowledge of the routes. migrations and their seasonal beaches.

The study found that the location of migratory routes from previous years and their summer area had 2 to 28 times more influence on the choice of a migration path as environmental factors such as monitoring the spring greenery, the thickness of the snow in autumn or topography.

"These animals seem to have a cognitive map of their migration routes and their seasonal beaches, which helps them navigate between seasonal beaches," says lead author Jerod. Merkle, Assistant Professor and Professor Knobloch in Migration Ecology. and conservation at the Department of Zoology and Physiology at the University of Waterloo.

The results have recently been published in Letters of ecology, a leading journal in the field of ecology. Co-authors of the article include Hall Sawyer, of Western EcoSystems Technology Inc.; Kevin Monteith and Samantha Dwinnell, UW Haub School of Environment and Natural Resources; Matthew Kauffman, U.S. Cooperative Fish and Wildlife Research Unit, Wyoming; and Gary Fralick, Wyoming Game and Fish Department.

Scientists had long assumed that migratory behavior was dictated by the availability of food resources and other external factors. Wherever you find resources, you will find species that exploit them, the theory said.

The UW team found that it was not so simple. Without the intrinsic factor of landscape memory for guiding deer between seasonal ranges, the long-distance corridors of the Green River Basin in western Wyoming, for example – sometimes exceeding 300 miles roundtrip – do not occur. would not exist in their current form.

"It seems that surfing on Green-Wave helps them determine when to move in a kind of" map "in their brain," said Merkle. "The timing of spring greening determines when an animal needs to migrate, but spatial memory determines where to migrate."

The discovery has important implications for conservation. Because the memory of the landscape is at the root of migratory behavior of the mule deer, the loss of a migrating population will also destroy the collective mental map of the herd on how to move in a landscape, making it very difficult to restore lost migration routes. Potential habitat areas will likely remain unused.

"This is another study that clearly shows that animals need to learn and remember how to make these incredible trips," said Kauffman, who heads the Wyoming Fish and Wildlife Research Unit, where research has been conducted. "This is essential for conservation, because it tells us that, to maintain a migration corridor, we must keep the specific animals that have the knowledge to make the trip."

The study confirms the findings of an article published in 2018 in the journal Science, led by a team led by UW, who discovered that an American sheep and moose were transferred without any evidence. Landscape knowledge can take several decades to a century to learn to migrate to vacant habitats.

Similarly, strategies such as off-site restoration or mitigation may be a failure if restored habitats are not "discovered" and integrated into individuals' memories.

The study also shows that biologists will not be able to successfully predict migration corridors – or manage populations optimally – based solely on environmental information or the quality of rangelands. It will be difficult for managers to assess potential conservation actions without directly collecting movement data, which is crucial information that reveals the knowledge of migration that animals carry in their head.

In addition, research shows that migrants can obtain better fodder benefits during spring migration by using the memory of a vast landscape, compared to migrants who simply rely on foraging signals in their area.

This suggests that the migratory routes we see today are optimized over several generations for surfing at the green wave in large landscapes. Migration corridors learned are not easily discoverable by animals if they can not access memories created by past generations.