I’m officially 2 months into my field season that will likely last until mid-October, so it’s about time for an update!
This year, Cache Crew (myself and my field assistant Tessie, a Yukoner herself) has been working hard to find out which patches of boreal forest certain squirrels are calling home this year. For a very territorial, vocal animal like the red squirrel, this sounds easier than it is. Although most squirrels traditionally defend a territory centered around a single food cache called a “midden”, this year there is relatively little food for them and lower densities of squirrels. This means that the remaining squirrels are spreading out a bit more trying to look for food that will fill their bellies right now AND fill their larders to sustain them for the winter.
Once we narrow down where squirrels are living, we are estimating how many white spruce cones (their #1 food source) are growing in spruce trees on their territories to get an idea of what is available for the squirrels to harvest, and also estimating how many cones they have leftover in their middens from previous years. With this information, we know how much stored energy they have stashed in the ground in addition to the potential food energy they might be able to take advantage of.
Sesame Street’s high calibre of training in counting has proven to be quite useful for this PhD! One spruce cone – ah ah ah!
But wait – what about the energy they store on their bodies? Traditionally we have thought of red squirrels as not carrying much body fat, since they don’t hibernate and don’t seem to put on that much weight heading into fall (unlike the Eastern grey squirrel or any hibernating ground squirrel/marmot who you may have encountered as a roly-poly feeding machine during “fat squirrel season”). We’re using some cool technology this year that is typically reserved for medical testing to investigate whether the body fat percentage changes across the food caching season. Have you ever had an MRI or known someone who has? We are using the same technology in squirrel-size to find out! Unlike an MRI, the machine we have doesn’t give us pictures, but it does give us readouts of % body fat, % lean mass (like muscle), and water content. All of this is coming together to give us a dynamic picture of how red squirrels manage energy throughout the food-caching season here in the southwest Yukon!
I was fortunate to be invited to present this research-in-progress at a special symposium on Food Caching in the Wild at the annual Canadian Society for Ecology & Evolution this summer at the University of Guelph. The symposium, organized by Alex Sutton & Dr Ryan Norris, was a fantastic forum to swap food caching findings, and a lovely little break from fieldwork to put it all into perspective.
The fireweed is starting to go to seed and the aspens are beginning to turn gold. Just like the plants know that fall is coming, so do the squirrels. We are starting to see new spruce cones, heavy and purplish-green, stuffed into holes in squirrel middens, and more and more are noticing these tree dwellers scurrying down the spruce with cones in their mouths to bring to their underground storage tunnels.
Stay tuned for updates as we move into the last half of the field season – and importantly, images of fieldwork that my current internet connectivity won’t allow to be uploaded.