Cool Critters: A packrat’s stash is a scientific treasure

Part of what you’ve heard about packrats is true. They snatch human objects in the night – a button, coins, shotgun shells, a ring. Then they obsessively stow them like Gollum, the bulgy-eyed creature in “Lord of the Rings.”

Yes, the packrat taketh away, but there’s more to the story. Did you know it also gives back in a remarkable way?

Packrats, also known as woodrats, are savvy collectors. Of the nine species that reside in North America, the bushy-tailed woodrat lives in our region and much of the Western United States.

Although close in size to their rat cousins, packrats belong to a rodent family more closely associated with hamsters, lemmings and voles, said Washington Department of Fish and Wildlife biologist Lindsay Welfelt.

The bushy-tailed version has wide, innocent-looking eyes, along with ears and whiskers whimsically large to its elfish cone-shaped face. The species is named for its hairy tail, unlike a city rat’s, which is naked and scaly.

“They’re cute,” said Welfelt, who occasionally encounters packrats while conducting field research in eastern Washington.

Like all packrat species, bushy-tailed woodrats confiscate naturally occurring materials such as sticks, plants, small bones and rocks – all within a radius of about 100 feet or so, she explained. When they live near humans, they also tend to snatch shiny items ranging from small jewelry and coins to nails and tin foil.

“Near humans, they can be a pest,” Welfelt said. On a larger scale, however, “they’re giving us something in return,” she explained.

And it’s here that the packrat story takes a fascinating turn. Packrats use all the loot they snatch – natural and manmade – to build homes, called middens.

“A midden is very intricate with several tunnels and cavities to sleep and store food,” according to the National Park Service, adding that packrats use their stockpiles for building materials, bedding and food.

In remote, dry locations, midden homes can be 5 feet tall and 9 feet in diameter. In less arid, human-populated areas such as the Inland Northwest, they’re considerably smaller, Welfelt noted.

Whether a packrat builds a mansion or bungalow, what does it use to hold the structure together? Its very own pee. Over time, the rodents’ syrupy urine hardens into a shiny shellac that blocks moisture and wind. Successive generations of packrats come along and add to the middens, making them larger and larger.

The result is a cluttered, yet well-designed dwelling for the packrat and a biological time capsule for scientists. From ancient seeds and animal remains to pottery fragments, the packrat’s collections can be preserved across millennia, providing a snapshot of the habitat back when it was alive.

“The contents of packrat middens represent the local environment at the time the material was gathered, and they can tell scientists a lot about past climates and environments,” the National Oceanic Atmospheric Administration states on its website.

In the past 50 years, researchers have collected and analyzed more than 3,000 fossil packrat middens in western North America, according to the United States Geological Survey, which maintains an online database of findings. The repository includes ancient middens uncovered in the City of Rocks National Reserve in southcentral Idaho, a midden hotspot.

Thanks to Idaho’s prehistoric rodent hoarders, scientists found that the area had no trees about 10,000 years ago. Then, less than 5,000 years ago, it shifted to pine and juniper woodlands. Scientists documented the scientific importance of the discovery in a 2020 study published in the journal Ecology and Evolution.

Closer to home, Washington State University wildlife biologist Rod Sayler recently got to observe a packrat’s exploits at his home near Clarkston after one assembled a nest behind a large planter on his patio.

“Packrats certainly are not stupid,” he said, adding that during a hot spell, his rodent visitor chose a well-shaded location that provided water in drip trays. The critter also hoarded bird seed from a feeder and stripped leaves off a fruit tree to sleep on.

Eventually, Sayler captured the packrat in a cage trap and released it in a wooded area along the Snake River. The encounter widened his perception of this much-maligned animal, he said.

“Sometimes I look back on my life and think that I know a lot. Other times I think that I’ve learned very little,” he explained. “But I do know this: if someone calls you a packrat, take it as a compliment.”