Welcome back to Birdbrained Science! I’m sure many of us are probably still shaking off the unstructured bed-rotting of winter break and trying to remember how to get back into the routine of being a student, so to kick off the spring semester, let’s talk memory!
Personally, I am a horrifically forgetful person. I have a terrible habit of putting things down (including sharp objects) and forgetting where they are moments later, and this week I lost my ID for probably the 100th time since freshman year. So hypothetically, if I were a UConn squirrel that could only survive the winter by tracking down (or recovering) stores of nuts and other foods that I buried back in the fall (in a process known as food-caching), I would probably die. How, then, do so many food-caching birds and squirrels manage to pull off this exact feat?
Just to be clear, when I talk about food-caching critters in this article, I’m specifically referring to animals who scatter-hoard. These species usually have broad diets; they eat lots of different kinds of food, which is usually found in many different places, so it makes sense for them to “scatter” their caches around. This is different than larder hoarding, where you have, say, American red squirrels, who mostly rely on a few pine trees for food and will create one giant pile of food scraps that they keep an eye on. Both strategies have their merits, but one requires more impressive memory feats than the other.
It’s a pretty widespread claim that the brains of food-caching animals actually get bigger right around the time they need to start burying food. Specifically, the hippocampus, which is the brain region most prominentlyinvolved with memory, is said to grow at the start of fall, giving animals more room to remember things. In fact, Natural Habitat Shorts, a series that produces animations about animal facts, actually has a video about this. I, however, found newer evidence that seems to contradict this (the original study came out in 1995; the newer studies are from 2000 or later), so I’m not totally convinced this is true. It’s quite possible that the original results were misinterpreted, as explained in a 2022 commentary by biology professor Vladimir V. Pravosudov.
But this doesn’t mean that the brain isn’t involved at all when it comes to recovering food stores. A study found that whenever black-capped chickadees cache food, the memory of each caching event gets stored in their hippocampus as a “barcode.” A “barcode” is a unique, specific combination of neurons firing. Each barcode seems to be linked to a particular caching event, and is reactivated when chickadees attempt to recover their caches.
Additionally, food-caching birds do seem to have a relatively larger hippocampus compared to their non-food-storing counterparts (just not one that grows during different seasons). A larger hippocampus seems to belinked to longer-lasting spatial memory in both humans and non-human animals, as was demonstrated in this 2001 study.
Speaking of spatial memory, many species appear to rely on exactly that to recover their stashes. Specifically, they seem to be using landmarks. A study conducted on gray squirrels planted flags to mark where squirrels had buried their caches. However, when these flags were moved, squirrels also moved the locations where they tried to dig up their food, relative to the changes in the flags’ positions. Similarly, an experiment conducted on Clark’s nutcrackers inside an aviary found that when various large objects within the aviary were moved, the nutcrackers had a much harder time finding their food stores.
Practice might also play a part in helping animals find their food. Gray squirrels in particular have also been observed visiting their caches before wintertime, with some even going so far as to dig up and then re-bury their stores. While they could just be making sure that they haven’t been robbed, at the same time, they’re also refreshing their memories of where they’ve buried their food.
Like so many processes in science, although we have some ideas, we don’t quite have the full picture. And like so many ideas in ecology, the exact memory mechanisms seem to vary by species (although there is a good deal of overlap). Regardless, I hope this inspired you to remember how to get back into the swing of things. See you all in another two weeks!