Tapping into the pack rat time machine: Rodents at Metropolis of Rocks depart behind 45,000-year-old time capsules for scientists to review | Regional Information


This is one case where a rodent’s predilection for hoarding, collecting, and thieving has been turned into a scientific treasure trove of information.

Specifically, these treasuries are mined in Idaho’s City of Rocks National Reserve near Almo.

Pack rats have a well-deserved reputation for stealing anything shiny and shiny, including pull-tabs, rings, watches or keys. But even these pack rats, who live far away from humans, comb their surroundings and collect something from everything – plants, sticks, stones, bones and dung – and pile it up in their habitat, the so-called dung heaps. You can’t help yourself. It is what they do. In the course of the life of a pack rat family, a dung heap can turn into a formidable mess. Although it looks like it’s stuck in a crack or notch, it’s rock solid.

What makes the Midden Blob tough and incredibly durable is pack rat pee. In the City of Rocks National Reserve, scientists studying piles of earth have dated the contents of some piles of earth to 45,000 years – particularly near the Twin Sister rock formations. The dung heaps can be found in small caves or behind weather-protected rock overhangs. In some cases, reaching the centers is achieved with the help of climbers.

“They’re hard as a rock, kind of black, big chunks, sometimes huge chunks of pack rat debris that have solidified, cemented by the crystallized urine of pack rats,” said Julio Betancourt, a half-retired scientist on the US Geological Survey of the contents of Studied and cataloged rubbish heaps in the West and in South America. “The pack rats only collect tons of stuff and don’t go very far to collect it – usually within 50 meters. The spatial resolution is really high. We’ve been exploring all sorts of things in these deposits. The most important thing is plant remains. “

Listening to Betancourt describe his midden degree is like taking a science college course.

This summer, Claire Veseth, a master naturalist from Boise, Idaho, was hiking with friends in the City of Rocks and noticing large piles of earth hanging from the rocks.

“I knocked on it with my walking stick and said, ‘This stuff is hard as a stone,'” said Veseth. “Then we noticed the silver shield underneath with a small circle nailed into the rock. It said ‘576’. I said someone would look at these things. “

Veseth contacted Betancourt and found out about his studies of dung heaps in the City of Rocks and elsewhere.

Pack rat pile

A tech climber recruited by researchers collects pieces of a pack rat pile in the City of Rocks National Reserve during a study. This dung heap was dated to an age of 5,200 years using radiocarbon.

“We asked him about Midden 576 and he said one layer was 4,100 years old, give or take 15 years and the other layer was 4,900 years old, give or take,” Veseth said. “I was thrilled to find out all of this information. I wonder what I miss in all these other places I’ve seen. “

Essentially, the crystallized urine becomes a time capsule, a snapshot of the ecology at the time the pack rat lived and gathered. A sample of piles of wood dated 10,000 years ago is on display in the visitor center of the City of Rocks in Almo.

“If you get a sample out of this dunghill, it’s rock hard,” said Betancourt. “We clean them very well. Then we bring it back to the lab and keep cleaning it up. Since the piss is crystalline urine and is water soluble, we throw it in a bucket of water and it will dissolve over a period of a week or two, releasing all of that plant debris that the pack rats have collected. Then we passed it through a geological sieve. Then place on a paper plate and dry. Then we sit there and sort. We separate things that we are going to analyze. Many of the plant fragments are in pretty good condition. We can often identify the species. “

Paleoecologists are enthusiastic about collecting well-preserved old plants. By studying the plants that have existed in the City of Rocks over the centuries, Betancourt and his team can track the climate and major vegetation changes that go back nearly 45,000 years.


In the City of Rocks National Reserve in Almo, pack rats peek out from behind a rock on their hut.

“At relatively high resolutions, we can tell when the plants migrated,” said Betancourt. “We did that for the Utah juniper, and we did that for the two main species of pinyon pine and the ponderosa pine in the central Rocky Mountains. What has always interested me are these isolated outposts of certain types. “

Betancourt cites the City of Rocks’ famous pinyon pines as an example of what the pack rat time machine reveals.

“We know when it got there,” he said. “We have a lot of dung heaps that haven’t had any pinyon in them for thousands of years, and then boom, you get to 2,800 and you get a few places where you can get pinyon but a lot of places where you don’t get pinyon. 700 years ago pinyon was omnipresent in the whole city of rocks. “

One question that helps researchers research the midden plant information is what has influenced fire regimes over the past few centuries: is it drought or wetter times with denser vegetation?

“Now that we have this vegetation record, it is an incredible luxury that we can address the chicken and egg issue,” said Betancourt. “Which comes first, the change in vegetation or the shift in the fire regime? And also the erosion in the sedimentation regime? “

A new research tool that has hit the market in recent years is metagenomics. This allows researchers to study a lot of genetic material from one location and potentially find more information about plants and animals that existed at a given time.

“It helps identify species and find things that we couldn’t have found otherwise, such as pathogens that infect both plants and animals that we could find in those heaps,” said Betancourt. “Lots of other animals go through these hollows and leave their own piss and droppings and hair and such. You can begin to get a slightly better view of the entire biotic community that contributes to it. “

Now that there is an archive of material from piles of trash across the west and in the City of Rocks, Betancourt said other scientists recently contacted him for details on a variety of research projects.

“People will say, ‘Hey Julio, I see, have you identified desert lavender from all these piles in the Sonoran Desert, and could I get this kind of food from you between 10,000 and now in this geographic area? I have this interesting hypothesis that I want to test. ‘ When I have it, I’ll give it to them, ”he said. “Not only do I do this, but everyone who has a rational plan to use the material.”

What about pack rats in 2021?

“These pack rats are still at work building a record. A time capsule is the right word, ”said Betancourt.