Chickadees are active, social birds that live in flocks and inhabit deciduous and mixed forests, open woods and parks. They feed on insects and seeds but prefer to cache their food away and eat it later, rather than consume it on the spot. In fact, chickadees hide thousands of food items every fall and rely on these hidden stores to get through the harsh winter times in the mountains of the western U.S.
For a chickadee, a highly developed spatial memory is clearly essential for survival. This fact led researchers to wonder whether spatial memory has a genetic basis in chickadees. If so, the ability to memorize the location of cached food would be under the influence of natural selection. The genetic basis for spatial memory has been demonstrated for humans and other mammals, but has not been identified in birds.
In a new study, published in the journal Current Biology, researchers investigated the genetic basis of individual variation in spatial cognition used by chickadees to recover food stores. The research involved a collaboration between scientists from the Cornell Lab of Ornithology, the University of Colorado Boulder, the University of Nevada, Reno, and the University of Oklahoma.
“We all use spatial memory to navigate our environment,” said study lead author Carrie Branch. “Without memory there’s no learning and an organism would have to start from scratch for every task. So, it really is life and death for these birds to be able to remember where they stashed their food. We’ve been able to show that natural selection is shaping their ability to remember locations.”
In order to quantify spatial memory ability in a population of wild Mountain Chickadees in California’s Sierra Nevada mountains, senior author Vladimir Pravosudov and his team at the University of Nevada, Reno, designed clusters of “smart” feeders that the birds could visit. Each feeder was equipped with a radio frequency identification sensor, and each of the 42 birds in the study was fitted with a leg tag, the size of a grain of rice, that gave off a unique identifying signal.
Birds were assigned to different feeders in the clusters. When a bird visited a feeder, the feedes sensor read the bird’s ID tag and, if it matched the feeder for that individual, a mechanism would open the door, and the bird could access a seed. The scientists recorded the number of attempts each bird made before it consistently went to the correct feeder.
“This is an effective system to test spatial learning and memory in hundreds of wild chickadees in their natural environment,” said Pravosudov. “We have previously shown that even very small variations in performance are associated with differences in survival.”
The researchers found that some chickadees took fewer attempts than others to learn the location of the feeder that delivered food to them. In other words, there was natural variation in the spatial memories of the birds. If natural selection is shaping chickadee memory, then one would expect to find variation in the trait: some chickadees are certainly better than others at remembering where their food is.
Furthermore, if there is a genetic basis to spatial memory then birds that perform the task better would have a survival advantage and would be more likely to produce offspring. This certainly appeared to be the case, with very small variations in performance being associated with differences in survival.
“Environment does still matter a lot in terms of shaping behavior, but our work here suggests that genes may create the brain structures, and then experience and learning can build on top of that,” explained Branch.
The study confirms that spatial memory in chickadees has a genetic basis and is selected for during the process of natural selection.
By Alison Bosman, Earth.com Staff Writer