Mountain knives have remarkable memories. A new study explains why

Food-storing mountain clams have some of the best spatial memory abilities in the animal kingdom.
Provided / Vladimir Pravosudov

RENO, Nevada — Have you lost your keys? Have you lost your glasses? Do you no longer remember where you parked the car? Maybe you wish you had the memory of a mountain tit.

In the warmer months, these half-ounce birds, with brains slightly larger than a pea, hide tens of thousands of food items such as seeds in tree bark, in lichens and crevices on the tree branches across the mountains. When winter arrives, they can remember the exact locations of their caches, a skill that helps them survive the bitter cold and deep snow.

In a new study published April 17 in the journal Current Biology, researchers from the University of Nevada, Reno and CU Boulder identify nearly a hundred genes related to birds’ spatial memory, or the ability to remember the locations of objects. The article also suggests that there may be a possible trade-off between having a solid long-term memory and being able to quickly abandon old memories to form new ones.



The findings could help biologists better understand the evolution of spatial memory in animals, including humans.

Vladimir Pravosudov is a professor of biology at the University of Nevada, Reno, and has been studying chickadees in the Sierra Nevada for 25 years.



“Using a field system for testing spatial learning in wild bird memory that we have used for many years, we worked with collaborators to find out which genes might influence how well a chickadee can learn spatial locations and remember,” Pravosudov said.

To evaluate the spatial memory of wild mountain tits, Pravosudov’s team designed a smart test. They put up multiple feeders, each containing eight bird feeders with seeds in the Sierra Nevada mountains. Each feeder has a port with a radio frequency reader that can detect a tag that researchers have placed on chickadees. The team then programmed each of the eight gates to open only for certain birds, so the chickadees had to remember the location of the correct feeders that would open for them.

Pravosudov and his team then measured the birds’ spatial memory by counting how many times each chickadee landed on the wrong feeders before retrieving the right one. Birds with better spatial memory have a lower error rate.

Using blood samples, the CU Boulder team also sequenced the complete genomes of 162 tagged chickadees that were tested for their spatial learning and memory abilities using the smart feeder arrays, creating the largest dataset ever collected for the evaluating the genetic basis of the cognitive ability of tits. . By comparing the birds’ genomes to their performance on the feeder test, the team identified 97 genes linked to chicks’ spatial learning and memory. Birds with specific genetic variants of these genes made fewer incorrect attempts before arriving at the designated feeders, compared to birds without them.

A large proportion of these genetic variants are associated with the formation of neurons in the hippocampus, a part of the brain responsible for learning and memory, said Sara Padula, co-author of the paper and PhD. student in the Department of Ecology and Evolutionary Biology at CU Boulder.

“Understanding the genetic basis of this trait will allow us to understand how the trait evolves,” said Scott Taylor, director of CU Boulder’s Mountain Research Station and associate professor in the Department of Ecology and Evolutionary Biology.

According to Taylor, the common ancestor of all North American chickadees was cached food. But of the seven species of chickadees now found in North America, two do not store food.

“They live in a milder environment where food is generally available all year round. Now that we know the gene regions that underlie spatial memory, we can look at what the variation looks like in these species that have lost caching,” Taylor said.

“This study has substantially improved our understanding of the genetics of spatial memory in birds and behavioral genetics more broadly,” said Georgy Semenov, co-author of the paper and research associate in the Department of Ecology and Evolutionary Biology.

Step down

Chickadees with exceptional spatial memory can live eight to nine years, which is a long time for a small bird, Taylor said. But having a good long-term memory can come at a price.

After a few days of performing the first task, Pravosudov’s research team assigned new feeders to the birds to test how well birds can learn new locations after being consistently rewarded at a different feeder, a test typically used to measure the assess cognitive flexibility.

Interestingly, chickadees from harsher, higher altitudes always seemed to perform worse on this ‘reversal’ test, despite having better spatial learning and memory abilities compared to birds from lower and milder altitudes. It seemed they had a harder time giving up their original memories and creating new ones.

“In a more variable environment, what our collaborators found suggests that chickadees with good long-term memory may be at a disadvantage,” Padula said.

A changing climate

Like many other habitats, mountains undergo rapid climate changes characterized by faster shifts between extreme drought and extreme snowfall. It is not clear how birds can adapt to such changes and how such changes can affect memory ability.

“Because of climate change, we might expect these selective pressures, which have shaped the special memory of chickadees for thousands of years, to shift significantly. By understanding the genetic basis of the trait, we can track changes in their genomes over time,” Taylor said.

“Tracking genetic changes associated with spatial cognition will allow us to better understand the evolutionary process associated with climate change,” Pravosudov said.

Pravosudov will continue to work with Taylor’s group at CU Boulder. The team has already set up the same experiment in the Rocky Mountains, where another population of mountain chickadees lives that has developed independently of the chickadees in the Sierra Nevada over the past million years.

The researchers will also look specifically at genes related to spatial memory and understand how frequencies of certain versions of a gene, or alleles, related to cognitive skills change over time with different climates.

“We can test whether selection on certain alleles is stronger in snow years and weaker in drought years, and also see changes over many years,” Pravosudov said.

Using these methods, researchers will be able to study climate-related evolutionary processes by focusing specifically on cognition and genes underlying cognition.

“We have a beautiful model that we can use to study the evolution of cognition in our mountainous backyards,” Pravosudov said.

The University of Nevada, Reno is a public research university committed to the promise of a future powered by knowledge. Founded in 1874, Nevada’s land-grant university serves 21,000 students. The university is a comprehensive doctoral university, classified as an R1 institution with very high research activity by the Carnegie Classification of Institutions of Higher Education. In addition, it has achieved the prestigious “Carnegie Engaged” rating, which reflects the impact of students and institutions on community engagement and service, fostered by extensive community and statewide partnerships. Since 2009, more than $800 million has been invested in state-of-the-art laboratories, residence halls and campus facilities. It is home to the University of Nevada, the Reno School of Medicine and Wolf Pack Athletics, and maintains a nationwide outreach mission and presence through programs such as the University of Nevada, Reno Extension, Nevada Bureau of Mines and Geology, Small Business Development Center, Nevada Seismological Laboratory, and is part of the Nevada System of Higher Education. Through its commitment to world-changing research, student success and outreach serving Nevada’s communities and businesses, the university has an impact across the state and around the world. For more information visit http://www.unr.edu.