Megan's Nature Nook
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With snow and colder weather upon us, many animals have either migrated to warmer areas, or snuggled into their winter dens for the next few months. Although many animals either migrate or hibernate for the winter we have quite a few hardy animals who stick it out and adapt to the changing weather. Each animal has their own strategy for surviving the cold months ahead. Storing up food for the upcoming winter is the top priority for most animals. However, how they gather and store their food varies with each species and some even have an extra trick up their sleeves to help them! Tree Squirrels Tree squirrels: Fox Squirrels, Gray Squirrels, Red Squirrels, and Flying Squirrels, all cache food for the winter. Red Squirrels and Flying Squirrels will usually store their food in a main area or have a few main caches. Fox and Gray Squirrels on the other hand participate in scatter hoarding, where they burry nuts in individual locations. This can add up to be hundreds or thousands of different hiding spots they have to remember. So how can they remember all of those hiding spots? Many trees only produce nuts in the fall. In order to ensure a large enough food supply to last them through the winter, squirrels have to gather and store as many nuts as they can before the snow falls and the weather gets too cold. To help them remember where they stored all their nuts, their brain does something extraordinary, it grows! Specifically, the hippocampus, which is the memory and spatial organization area of the brain, increases 15% in size in the fall. This increase helps them to remember where a majority of those hundreds or thousands of nuts they scatter hoarded are. The increased brain size especially helps them after the snow has fallen, making it harder to sniff out nuts and making the squirrels easier targets for predators to spot and catch. Squirrels do some other interesting things that help them in their food storage habits. Once they find a nut, they will hold it in their paws and shake it to weigh it and determine if it has any insects in it. If it is light weight, most likely an insect is inside and has been eating it. If that is the case, they will eat the nut and insects right away because they know if they cache it, the insects may eat it before they get a chance to. If the nut is heavy with no insects, they will proceed to find a hiding spot for it. Studies have shown that squirrels will categorize where certain types of nuts are stored. They’ll have walnuts in one area and acorns in another which may help them to better remember the hiding spots since they’re more organized. After the initial hiding they will continue to interact with their caches, visiting spots where they’ve been buried, sniffing around, and even digging up and reburying nuts in a new spot. This can help them to better remember where each nut is hidden and build their mental nut map. It is also thought that digging fake holes and digging up and reburying nuts might deceive any onlookers that may try to steal their caches. Chickadees Squirrels aren’t the only critters whose brains grow to help with food caching. In late summer and early fall the brains of Chickadees grow. The brain growth is happening in the hippocampus just like the squirrels and increases by approximately 30% by adding new nerve cells. In Chickadees, neurons are replaced periodically. Studies suggest that they are able to discard cells that have old memories and replace them with new cells where they can store new memories, such as where they hid a seed. Then in the spring when they no longer have such a need for hiding spot memory, their hippocampus shrinks back down to normal size. Shrews Unlike squirrels and Chickadees, shrews have a different brain winter survival tactic. Instead of growing part of their brain to help with the memory of food caches, they do the opposite. Their skulls and brains shrink! Their skulls will shrink an average of 15% and they loose between 20-30% of brain mass. The joints between the bones of the skull reabsorb tissue during the fall and winter, the tissue will then regenerate in the spring, “growing” the skull back to almost its former size. The skulls and brains aren’t the only things that shrink for the winter in shrews. Other organs lose mass and the spine shortens, reducing the overall body mass of the shrew by about 18%. This act of shrinking in the winter is call Dehnel’s Phenomenon. Luckily for the shrew, in the spring their body mass will rebound to 83% of what it was previously. So, they will be slightly smaller than the previous year, but larger than they were during the winter. It is thought that the reason for this phenomenon may be to conserve energy. Less mass means the need for less food. Shrews are one of the smallest mammals yet have a high metabolic rate causing the need to eat every few hours. Since they cannot migrate far distances to warmer weather and don’t hibernate, winter shrinkage helps them to survive the cold winters. Shrews live an average of 1-2 years so the compounding shrinkage year after year doesn’t really affect them. Who knew all these little critters could do such amazing things to help them survive winter?
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