Nature Notes: Fall Feeding Frenzy
This month is known as Binaakwii-giizis, or “Leaves Changing Color Moon”, to the Fond du Lac Band of Ojibwe. The beautiful weather over the first couple days of October made for some breath-taking scenery of brilliant yellows against a bright blue sky and dark blue waters. Soon the yellow of our aspens will be replaced by the golden shimmer of our tamaracks. Enjoy the view now, for by the end of the month, we’ll be greeting the barren landscape of winter.
The animals that remain in our cold environment for winter are busy preparing for the season. Throughout the next month, we’ll focus on three animals that uniquely prepare for winter: squirrels, beavers, and winter birds. We’ll kick off our fall feeding frenzy by taking a look at how squirrels are preparing for the season ahead.
Above: Marilyn Lee caught this red squirrel adding to its larder. Below: A midden left on a look-out stump.
Squirrels are busy storing, or caching, food. Our two most common squirrels, eastern gray squirrels and red squirrels, have very different behaviors when it comes to food. Gray squirrels tend to favor nuts, like acorns, while red squirrels tend to favor other seeds, like those from pine cones. Gray squirrels are “scatter hoarders” which means they store small amounts of food in numerous locations. They have excellent spatial memories and rely on landmarks to get them close to their hidden caches before using smell to hone in on the treasure. Red squirrels on the other hand, are “larder hoarders”, which means they store large amounts of food in one or a few piles. They rely on their superb sense of smell to find their food, above and below ground. They can even sniff out seeds under multiple feet of snow! Seeing large piles of pinecones indicates the presence of red squirrels, as do their middens, or the “waste” piles left behind as they pick the seeds out of a pinecone. Red squirrels, which are smaller in size than gray squirrels and are often prey for other species, tend to eat while “on guard”, so you’ll often find these middens below a low branch, log, or stump where the squirrel can keep an eye out for predators while it eats.
Not only do gray squirrels have a stronger affinity for acorns, but they also have a preference for types of acorns! We have two categories of oak trees here in Minnesota: red oaks and white oaks. We have three types of white oaks and four types of red oaks throughout the state. Red oaks have pointed lobes on their leaves and their acorns take two years to develop, are rich in fat, and are high in tannins. Tannins are bitter-tasting compounds that are believed to delay germination in acorns, so red oak acorns typically fall to the ground during autumn but do not germinate until the following spring. White oaks have rounded lobes on their leaves and their acorns develop in one year, are low in tannins, low in fat, and germinate right away when they fall to the ground in the autumn.
In a study tracking acorn dispersal by squirrels, scientists found that squirrels treated acorns from these two groups of oak trees differently. Up to 85% of the white oak acorns collected by squirrels were eaten shortly after discovery and 15% were stored for later. If squirrels were to wait to eat white oak acorns, they would lose much of their fat stores and nutrients, as these are used up in the process of germination. Only 40% of red oak acorns are eaten right away, while 60% are buried for later. While these red oak acorns are buried in the soil, groundwater leaches out the tannins, meaning they become much tastier (less bitter) later in winter then they are in autumn. They have relatively the same amount of fat and nutrients if eaten before the spring. Pretty smart, huh?! Squirrels can bury over 1000 acorns in preparation for winter, but they won’t recover all of them. In fact, the study found that up to 72% of the acorns may not be recovered! The ones they don’t dig up have already been “planted” by the squirrels and help in the regeneration and dispersal of our oak trees.
There is another interesting relationship between oak trees, their acorns, and the rodents that eat them. Many scientists have explored the connection between the number of acorns produced in the autumn and the population of acorn-eating rodents the following summer. It turns out, there is a cyclic predator-prey type of relationship (without the predation, of course). Oaks are a type of mast tree. Mast is the fruit of a forest tree, such as acorns or hickory nuts. Oaks do not always produce the same amount of acorns each year – some years there are only a handful while other years have very high yields. Mast trees synch up, so when one type of oak is having a year with more acorns than usual (a mast year), they all are! Depending on the type of oaks, mast years occur every 2-5 years. Let’s explore how this would be an evolutionary advantage to the tree.
Squirrels aren’t the only ones caching food for winter. Chipmunks are furiously working to fill their dens with enough food to last through the winter. Busy beavers are making their rounds, cutting down trees and dragging the branches back to their lodges. This cache of sticks will serve as the beaver’s fridge for winter, allowing underwater access to this food source once the ice has formed on our lakes. Even chickadees, nuthatches, and blue jays are busy caching food in the nooks and crannies of our trees.
So get outside this month to see who you can catch in the act of preparing for winter! Soak in that last bit of autumn sunshine while it lasts! Make sure to come back to our blog next week and check out what the beavers are up to & how they prepare for a long, cold, wet winter. Enjoy!
This chipmunk, captured by Marcia Adair, has large cheek pouches that helps it efficiently gather & store food for winter. Marcia says her name is Chiplet! 🙂 Do you have a frequent visitor in your yard?