From University of Wyoming\r\n\r\nWYOMING \u2013 Mule deer migration is important to wildlife biologists and other interested parties. Oil and gas exploration companies want to know if their operations are having an impact on mule deer habitat, for one. Highway overpasses are also planned and plotted according to exactly where big game travel to and from.\r\n\r\nSo, just what is driving mule deer to get on the move\u2014when and where? How do big game animals know where to migrate across hundreds of miles of vast Wyoming landscapes year after year?\r\n\r\nAmong scientists, there are two camps of thought. First is that animals use local cues within their vicinity to determine where to migrate. Animals might move up to areas with greener forage\u2014often termed greenwave surfing\u00ad\u2014or move down from mountains with deeper snow. The second idea is that animals develop memory of the landscape where they live and then use that information to guide their movements.\r\n\r\nRecent research from the University of Wyoming has found that memory explains much of deer behavior during migration: Mule deer navigate in spring and fall mostly by using their knowledge of past migration routes and seasonal ranges.\r\n\r\nThe study found that the location of past years\u2019 migratory route and summer range had 2-28 times more influence on a deer\u2019s choice of a migration path than environmental factors such as tracking spring green-up, autumn snow depth or topography.\r\n\r\n\u201cThese animals appear to have a cognitive map of their migration routes and seasonal ranges, which helps them navigate tens to hundreds of miles between seasonal ranges,\u201d says the lead author of the paper, Jerod Merkle, assistant professor and Knobloch Professor in Migration Ecology and Conservation in the Department of Zoology and Physiology at UW.\r\n\r\nThe findings recently were published in\u00a0Ecology Letters, a leading journal within the field of ecology. Coauthors of the paper included Hall Sawyer, with Western EcoSystems Technology Inc.; Kevin Monteith and Samantha Dwinnell, with UW\u2019s Haub School of Environment and Natural Resources; Matthew Kauffman, with the U.S. Geological Survey Wyoming Cooperative Fish and Wildlife Research Unit at UW; and Gary Fralick, with the Wyoming Game and Fish Department.\r\n\r\nScientists had long presumed that migratory behavior was dictated by availability of food resources and other external factors. Where you find resources, you will find species that exploit them, the theory went.\r\n\r\nThe UW team found it is not that simple. Without the intrinsic factor of landscape memory to guide deer between seasonal ranges, the long-distance corridors of western Wyoming\u2019s Green River Basin, for example\u2014exceeding 300 miles roundtrip in some cases\u2014would not exist in their present form.\r\n\r\n\u201cIt appears that greenwave surfing helps them determine when to move within a kind of \u2018map\u2019 in their brain,\u201d Merkle says. \u201cThe timing of spring green-up determines when an animal should migrate, but spatial memory determines where to migrate.\u201d\r\n\r\nThe finding has important conservation implications. Because landscape memory so strongly underlies mule deer migratory behavior, the loss of a migratory population also will destroy the herd\u2019s collective mental map of how to move within a landscape, making it very difficult to restore lost migration routes. Patches of potential habitat likely will go unused.\r\n\r\n\u201cThis is yet another study that makes clear that animals must learn and remember how to make these incredible journeys,\u201d says Kauffman, who leads the Wyoming Cooperative Fish and Wildlife Research Unit, where the research was conducted. \u201cThis is critical for conservation, because it tells us that, to conserve a migration corridor, we need to conserve the specific animals who have the knowledge necessary to make the journey.\u201d\r\n\r\nThe study bolsters the findings of a\u00a02018 paper\u00a0in the journal Science by a UW-led team that found translocated bighorn sheep and moose with no knowledge of the landscape can take anywhere from several decades to a century to learn how to migrate to vacant habitats.\r\n\r\nSimilarly, strategies such as offsite restoration or mitigation may be unsuccessful if restored habitats are not \u201cdiscovered\u201d and integrated into the memory of individuals.\r\n\r\nThe study further makes a case that biologists will not be able to successfully predict migration corridors\u2014or optimally manage populations\u2014based on environmental information or range quality alone. Managers will find it difficult to evaluate potential conservation actions without directly gathering movement data, crucial information that reveals the migration knowledge that animals carry around in their heads.\r\n\r\nMoreover, the research shows that migrants can obtain greater forage benefits during spring migration using memory of a vast landscape, compared to migrants that rely simply on foraging cues in their local area.\r\n\r\nThis suggests that the migratory routes we see today are optimized across generations for greenwave surfing in large landscapes. These learned migration corridors are not readily discoverable by animals if they cannot access the memories established by past generations.