How the gathering habits of squirrel unique to Arizona could be the key to saving it

KJZZ | By Mark Brodie
Published July 29, 2024


Arizona Game And Fish DepartmentMount Graham red squirrel.

How a species of squirrel unique to a region of Arizona collects its food could provide some clues about the best ways to protect it going forward. And new research sheds some light on how these squirrels hoard their food.

The Mt. Graham Red Squirrel has experienced disturbances over the past several years, including from fires and insect outbreaks. Over the last three decades, their populations have declined significantly. Sean Mahoney says as of December 2023, there were 144 of them.

Mahoney is a research scientist in the School of Natural Resources and the Environment at the University of Arizona and is also affiliated with the Mt. Graham Biology Programs. He spoke with my The Show — starting with what he was trying to figure out with this research.

Sally HenkelSean Mahoney

SEAN MAHONEY: Yeah, so finding food is probably the most important thing that an animal needs to do. And finding food can be quite a challenge for an animal and it can be especially challenging during periods of scarcity like during the winter when food is just highly limited.

And so some animals have just said, OK, I'm not gonna deal so much with trying to find food in the winter and they just decide to hibernate. But there are a lot of animals that don't hibernate. And so they need to still find food, during periods of scarcity, like during the winter.

And there are three main ways that animals will do this. They'll hoard food. And one strategy of hoarding food is referred to as larder hoarding. And this is when an animal takes a whole lot of food and stores it at a central location and then they can return to that central location in the winter and access food.

And then animals will also scatter hoard food. And this is when animals take smaller amounts of food and hide them across larger areas. And then animals also will do what we've referred to as mixed hoarding. And this is when they'll hoard food, but also scatter hoard food. And an example of this are red squirrels in eastern Arizona and on Mount Graham.

And so hoarding food is really important for how animals survive through the winter when food is really limited on the landscape. And so it can be a really important behavior to understand, especially in a conservation context because it allows us to understand how animals can survive during these periods of scarcity, like during the winter.

MARK BRODIE: And it seems as though you found that at least for some of them, like there's some amount of flexibility with this, like it's not a, not a system that is set in stone.

MAHONEY: Yeah. So, so what we did in our study was we were primarily interested in understanding this behavior in red squirrels because they exhibit this, this mixed strategy and it can offer insights into their, their conservation planning. We also wanted to understand this behavior in a broader context for mammals more broadly.

And when we looked at the evolution of the behavior more broadly within mammals, we found three main patterns emerge from that, from that analysis. And what we found was that the hoarding behavior was related to something about the climate. So if a species was living in colder climates, they were more like, with more precipitation, they were more likely to larder hoard their food rather than scatter hoard their food. So it seems to be related to precipitation and temperature.

And then a third factor that emerged from that analysis was population density. And mammals that were living at higher population densities, so if there were just more individuals of the same species in the area, they were more likely to larder hoard their food. And so, so given that, given that we found that at this broad analysis of, of other mammals, we wanted to explicitly test that within Mount Graham red squirrels.

And to do that, we used a quarter-century data set of Mount Graham red squirrel world data. So we had their population density and the number of cones that they stored in their middens for about 25 years.

And what we found was that in years when the population density was really high, Mount Graham red squirrels would store more cones in their midden. And this supports the hypothesis that they're experiencing more competition at these higher population densities. And that means the squirrels need to invest more, they need to put more food in their midden and then rigorously defend it from competitors that might try to steal the food from them so that they can survive the winter.

But then, interestingly, we did not find that temperature and precipitation was related to the number of cones that they would store in the midden.

BRODIE: So what does all of this tell you about the efforts to conserve and preserve the species of squirrel?

MAHONEY: So this finding, it's, it's an interesting finding in that at these higher population densities, squirrels tend to put more cones into their midden. And at these lower population densities, which they're living at now, they're living at lower population densities. They're not putting as much food into their midden.

And this sort of suggests that they might be shifting to another behavior because they still need to access food during these periods of, of scarcity like in the winter. And anecdotally, what we have noticed is that the, the red squirrels, they still maintain that main midden, but they also have started to develop these kind of smaller middens, which we refer to as satellite middens, around that main larder.

And although this isn't full-on scatter hoarding necessarily, it does sort of suggest that it's, it's kind of this modified scatter hoarding behavior. And what this means is that right now, the critical habitat designation for this endangered subspecies is written to protect habitat under the assumption that squirrels are building this central midden. But if they start to shift towards large, towards scatter hoarding, excuse me, then we may need to tweak the critical habitat designations to more better accommodate the habitat needs of the red squirrel.

BRODIE: How big of a shift would that be?

MAHONEY: That would be quite a legal challenge that would involve changing the, the critical habitat designation that's written by the U.S. Fish and Wildlife Service. So that would be, it would be quite a challenge to do.

And I'm and I'm not suggesting that that needs to happen now. Mainly what I'm suggesting is that it's important to continue the monitoring of the, the foraging behavior of the red squirrel just to keep track of how their food storage behavior might be shifting in response to these population density changes that we're seeing.