For chickadees, memory is a product of natural selection

On the mountaintops of the Sierra Nevadas, mountain chickadees (Poecile gambeli) create food caches to survive the winter, and they rely on their memories to find them.

Researchers had already known that in places of higher elevation or with harsher winters, chickadees often rely more on these caches. In previous research, they found that chickadees in these areas had a larger hippocampus, a part of the brain that helps with memory, and they had more neurons in their hippocampus than other chickadees.

Recently, biologists found these traits relating to good memory are gained through natural selection.

In the study published in Current Biology, they used passive integrative transponder tags and feeders equipped with radio frequency identification devices. The tagged birds were assigned to one of eight feeders. When they attempted to get food from a feeder that they weren’t assigned to, the machine recorded it but no food came out.

“Any time a bird lands, it records the time and ID of every bird,” said Vladimir Pravosudov,biology professor at the University of Nevada, Reno, and the study’s corresponding author.

The team recorded how long it took for the birds to learn which feeder gave them food and how well they remembered this the following days. They also determined which of the birds did and did not survive the following year and compared how those birds had done on the previous memory test. “Birds that survived did much better than birds that died,” Pravosudov said.

For the birds that survived, the researchers then retested them to see if their memory changed with age. “There was no difference between performance of the same birds when they were juveniles during the first test year and the next year when they were adults,” he said. This suggested that the trait of having a good memory is a naturally selected trait, unique to the bird. At the same time, adults, who survived their first winter, showed better memory compared to a cohort of new juveniles. Overall, he said, the research showed differences in memory have survival consequences.

Pravosudov said this is the first study to show cognition is a trait directly affected by natural selection, just like color or tail length.

The results may apply to other species, he said, but the chickadee system proved ideal for the study.

“There have been speculation and attempts by other people for evaluation of intelligence shaped by natural selection, but some of them were not successful,” he said. “I think the reason our system is successful is because chickadees are a good model.”