Tradeoffs between learning and memory in mountain chickadees

Mountain chickadee, Poecile gambeli. Photo by Nick Athanas.

This week's paper is in Animal Behaviour and comes out of the Pravosudov lab at the University of Nevada at Reno, lead authored by Rebecca Croston. Mountain chickadees, Poecile gambeli, live in the Western USA and Canada where they occur from low elevations up into the Sierras. Previous research from the Pravosudov lab has shown that the high elevation chickadees (which experience harsher climates) have better spatial memory and larger hippocampi (the brain region associated with spatial memory), than low elevation chickadees. This is thought to be because high elevation chickadees must cache more food to make it through the winter, and therefore they must have better spatial memory to locate all those food caches. In this particular paper the authors examined the "cognitive flexibility" of high and low elevation chickadees. Chickadees were captured in the field and fitted with individual PIT tags. These PIT tags were registered by feeder boxes that identified and recorded the bird that landed, and determined whether that individual is allowed access to food. (As a side note, this PIT tag and feeder technology is such a cool way that field research on animal behavior is being transformed right now!) The authors put arrays of 8 feeder boxes out in the field, and chickadees only got food when they landed on their assigned "correct" box. They therefore couldn't follow each other to the correct feeder box, because the PIT tag system assigned the correct box to be different for each bird. After a bird learned the correct box, it was then tested for behavioral flexibility using a reversal task, in that the "correct" box was changed to a different box in the array.

The authors found that high and low elevation chickadees performed equally on the initial learning task (which is contrary to their previous reported results that high elevation chickadees perform better at spatial learning tasks), and high elevation chickadees are much worse at the reversal learning task. The authors suggest that selection for spatial memory abilities and the associated larger hippocampi, may be a trade-off with cognitive flexibility. Perhaps the high elevation birds are really good at remembering initial food cache locations, but this limits their ability to learn novel caches. I don't know that I buy this. The authors say that it was a harsher year than other years, as a potential explanation for the lack of a difference in initial learning between high and low elevation chickadees, which is incongruous with their previous research. It seems possible to me that this reduced reversal learning is also a consequence of some other factor. The concept that selection for memory may limit flexibility is, however, interesting. I hope the Pravosudov lab pursues this further to really pull apart what factors are at play.