Usually, forgetting where you put your coffee cup down doesn’t have a major impact on the rest of your life – you can easily retrieve another cup of coffee (and find the other one later, in a cabinet for some reason). For food-caching mountain chickadees residing at high elevations in the Sierra ΒιΆΉΣ³» mountains, however, the ability to remember where they cached thousands of seeds during the fall may lead to a longer life by increasing their ability to survive harsh, snowy winters, according to research published this week in Science.
Biologists have long assumed that “smarter” animals will live longer, because they can better adapt to unpredictable events or changes to their environment. As climate change starts to make its impact felt, changing many aspects of ecosystem ecology, testing this assumption is increasingly important. Previous studies comparing different species have been difficult to draw conclusions from because of the increased variables that separate species. Some studies comparing individuals in a given species have even drawn the opposite conclusion, that larger brain size is correlated with a shorter lifespan.
“Our study is unique because instead of relying on broad measures of cognitive ability, such as brain size, we compared performance on an ecologically relevant spatial task to lifespan within a single population,” Joseph Welklin, a postdoctoral researcher at the ΒιΆΉΣ³» and lead author of the study, said.
In the study published in Science, titled, “Spatial cognitive ability is associated with longevity in food-caching chickadees,” researchers tracked the lifespans of 227 wild mountain chickadees over the last ten years and tested their spatial learning and memory ability every year. The article is featured on the cover of the journal.
This research was done in the Cognitive and Behavioral Ecology Lab run by Vladimir Pravosudov in the Department of Biology at the ΒιΆΉΣ³». Pravosudov has studied mountain chickadees in the Sierra for more than 20 years, resulting in a significant understanding of how important spatial memory is for food-caching chickadees. Among a slew of related research findings, the researchers had shown in previous studies that chickadees with better spatial learning and memory are more likely to survive their first winter of life and that spatial learning and memory abilities are highly heritable and have genetic basis.
Mountain chickadees are a non-migratory food-caching species that store thousands of food items (mostly pine seeds) during the fall, scattering them one food item at a time in caches around their home ranges. Unlike migratory species, chickadees spend their entire lives including winters in the same locations and food caches are critical for their overwinter survival. Scattering numerous food caches around the entire home range and storing one item in each cache serves as a strategy against cache theft as thieves would only be able to steal a few caches at best, while the chickadees themselves rely, at least in part, on their spatial memory to find their cached food. As such, spatial learning and memory abilities are critical for chickadee survival, and the harsher the winter environment, the more important memory is. These small birds need to eat all the time during the shorter winter days and failing to find food either early in the morning or during the frequent Sierra snowstorms would be fatal.
To measure spatial learning and memory ability, researchers used “smart” feeder arrays of eight feeders. The feeders were equipped with radiofrequency identification (RFID), and each fall and winter, wild chickadees were caught and tagged with Passive Integrated Transponder (PIT) tags. The transponder tags communicate with the feeders, tracking when each individual bird landed on each feeder, and releasing a seed for the bird to eat or cache. At first, all the feeders opened to all birds with tags, so the chickadees could be familiarized with the feeder mechanisms (land on the feeder and receive a seed). Then, as the experiment progressed, only one feeder opened for an individual chickadee throughout the rest of the experiment. When a bird visited a non-rewarding feeder, that information is tracked, too.
Chickadees with better spatial cognition will remember which feeder is the right feeder very quickly and will make fewer and fewer errors (visits to the non-rewarding feeders) with each visit, while those with worse spatial cognition will continue visiting the wrong feeders for longer periods of time. The researchers also tracked cognitive flexibility by measuring performance on a reversal learning task. This was studied by allowing an individual to receive food from a given feeder in the array, then after a few days, changing which feeder in the array rewards the chickadee. The individual is expected to learn the change and stop visiting the previously rewarding feeder.
Mountain chickadees are highly resident birds that spend their entire life in the same home range, so birds not detected for more than a full year at smart feeders, during annual banding periods or during breeding at smart nestboxes in the study area, were assumed to be dead.
The researchers found that chickadees with the best spatial cognition involved in food caching lived on average two years longer than chickadees with the worst spatial cognition. In contrast, cognitive flexibility, which is a trait not involved in food caching, was not associated with survival and lifespan.
“This is an exciting finding because it provides empirical support for the common assumption that smarter individuals live longer lives,” Welklin said. “Intelligence and survival in mountain chickadees is based on their spatial memory abilities – those individuals that can remember where they’ve hidden seeds are more likely to survive the long winters at high elevations, whereas those individuals with poor spatial memory are more likely to starve. It’s a harsh world out there for a 12-gram bird that lives in mountainous conditions where up to 17 feet of accumulated snow is possible in some winters.”
“Combined with our previous results showing that spatial cognition is critical for survival during chickadee’s first year of life, and that variation in cognitive abilities is associated with genetic differences, this study shows that these abilities are under direct natural selection at high elevations associated with harsh winters,” Pravosudov, who supervised the study, said. “Birds with better spatial cognition have better survival and longer lifespans allowing them to produce more offspring with good cognitive abilities during their lifetime compared to chickadees with worse spatial abilities.”
This research is a culmination of many years of field work when birds were tested on spatial memory and followed throughout the entire year. Such intense field work involved many graduate students and postdoctoral scholars in Pravosudov’s lab including Ben Sonnenberg, Virginia Heinen, Angela Pitera, Lauren Benedict, and Lauren Whitenack as well as long-term collaborators Carrie Branch (University of Western Ontario, Canada) and Eli Bridge (University of Oklahoma).
Next steps will consider whether cognition-based survival in chickadees varies between years depending on winter climate and whether winter climate affects strength of selection.
