Wyoming Migration Initiative

Migration tracking week 9 🦌🦌🦌🦌🦌🦌🦌🦌🦌 Deer 665 has arrived on summer range! The five-year old mule deer finally reached Teton Valley, Idaho on June 8 and gave birth to her twin fawns on June 9. This is the first time she has given birth in Idaho. Amazingly, June 8 is also the date she arrived on summer range in 2024 and 2025.

This is the last update for Deer 665’s spring 2026 migration. Assuming she has a successful summer, we’ll share her next migration journey when the snow flies in autumn. If you enjoyed tracking Deer 665 with us, be sure to hit the follow button and help us share migration science with the world.

MIGRATION SUMMARY
All told, this spring Deer 665 migrated about roughly 197 miles in 61 days, with 45 of those days foraging in stopover habitat. That’s almost three-quarters of her migration spent selecting for the most nutritious springtime sprouts. These plants set her up for successful birthing, lactation, and survival in the coming winter.

Across Deer 665’s full spring migration, she made seven crossings of four highways, along with navigating more than 100 fences, swimming the Green River and Snake River and traversing an arm of the Continental Divide.

Starting from winter range in Superior, Wyoming at 7,100 feet, her lowest elevation on the migration trail was 6,070 feet during her nighttime crossing of the Snake River. Her highest elevation traversed was about 9,200 feet on a ridge south of Teton Pass.

PLAY-BY-PLAY FOR WEEK 9
Deer 665 began week nine of her migration near the switchback on the western part of the Teton Pass highway. She hung out there from June 4-8, foraging in the woods at a stopover measuring about one mile in length.

On the night of June 7-8, she set off on her final migration push along Trail Creek and the highway. She crossed the road to the north for about 30 minutes, only to return to the south side.

She then migrated about eight miles downhill, losing 600 feet of elevation.

After traveling for 59 days and nearly 200 miles in Wyoming, she crossed into Idaho at 5 AM on June 8.

She then joined the path of an electrical transmission line through the forest. This convenient route for Deer 665 follows the power line transmitting energy from Palisades Dam into Jackson Hole to power its ski areas, houses, and businesses. In a way, Deer 665 is also using this transmission line to get the energy she needs in the form of plants.

Deer 665 next migrated within a quarter mile of a golf course subdivision on the outskirts of Victor, Idaho. She traveled about halfway through the forested hills that bound the southern end of Teton Valley.

Then on June 9 she doubled back to the east where a cluster of points suggests she gave birth to her twin fawns. We do not have visual confirmation of the fawns, but they showed up on a field ultrasound by in March, 2026.

The birth zone started out measuring about 300 feet in diameter on June 9, then roughly doubled in area by a week later, and doubled again by the end of June. This widening circle likely corresponds to the increasing mobility and expanding world of her fawns, the next generation of migratory mule deer.

SUPER-LONG MIGRATION
Deer 665’s final summer range is near developed areas, yet her ultra-long-distance migration shows she is one of the most remarkable mule deer in the Mountain West. While long-distance migrators tend to be fatter and make up more of this herd, migrations of all distances are important for maintaining abundant big game populations.

Deer 665 is only the second mule deer that we have ever documented migrating from Wyoming’s Red Desert across the Teton Range and into Idaho.

The other deer was Deer 255, who we tracked from 2018-2024. Deer 255’s longest migration was approximately 242 miles, about 20 miles longer than Deer 665 has ever ventured.

Deer 665 didn’t quite match her longest migration of 223 miles to Ririe, Idaho completed in 2022. Yet at nine weeks of travel and stopovers, spring 2026 was one of her lengthiest migration durations. In 2023-2025, she typically migrated for only five weeks. In 2026 she departed winter range nearly a month earlier than usual given the early arrival of spring, which accounts for the longer time on the trail.

While Deer 665 is just one animal, she helps us empathize with the challenges that all migrating species face as they strive to complete their seasonal cycles.

THANK YOU to everyone who has followed, liked, shared, and commented. Every one of you has added to the strength of Deer 665’s story. We’re grateful for your curiosity about the incredible migrations that big game mammals make. We can all do our part to use this knowledge to keep wild migrations intact for future generations.

The data for this map is thanks to collaboration between our team at the University of Wyoming and biologists with the Wyoming Game and Fish Department, Monteith Shop, Bureau of Land Management - Wyoming, and USGS Cooperative Fish and Wildlife Research Units.

Cartography by our Wild Migrations atlas partners at the Department of Geography, University of Oregon InfoGraphics lab, especially Clare Otcasek and Joanna Merson, and WMI’s Ian Freeman.