Problem-Solving Squirrels

Vicki’s home-built,
squirrel-proof
bird feeder.

Welcome back. In one of my earliest blog posts (Lawn, Garden & Squirrels Photo Addendum), which was an addendum to a post voted exceptionally humorous (Time for Lawn and Garden), I described my wife Vicki’s struggles to defend birdseed from squirrels.

After failing with commercially available, squirrel-proof bird feeders, she painted and stood a pvc tube, about 8-foot tall, 8-inch diameter, on our deck and hung bird feeders and faux vegetation from its top.

As I wrote: Was it fear of jumping, missing and falling that restrained the squirrels, or were they just laughing too hard? Whatever it was, it worked for a couple of days.
 

Oops. A squirrel
made the leap.

Although I needed no further insight concerning squirrels’ problem-solving ability, researchers from the U.K.’s University of Exeter felt differently. They set out to examine how memory, together with behavioral traits, enhance squirrels’ problem-solving efficiency.

Testing Squirrels’ Memory
The researchers assessed five gray squirrels’ ability to retrieve food from the same puzzle box the squirrels had overcome 22 months earlier as well as from a physically dissimilar puzzle box that required the same actions for success.

The original puzzle box was a transparent plexiglass cube, outer dimensions about 10 inches. Ten holes were aligned vertically on each side, and 10 levers were inserted through holes on opposite sides. One end of each lever had a container for a hazelnut positioned just inside the box; 5 levers held a nut, 5 were empty. The box stood on legs, allowing space for squirrels to obtain nuts that fell from the containers.
 

Squirrel-testing puzzle boxes. Top: original box, first used 22 months earlier; Bottom: two views of new box. (Photo from link.springer.com/article/10.1007%2Fs10071-017-1113-7)

The most effective squirrel behaviors to obtain a nut were pushing the end of a lever near the container or pulling the opposite end. Pulling the near end or pushing the far end wouldn’t work.
 
The new puzzle box added for the study was an A-frame, four-sided triangular prism. There were only 5 levers inserted through side holes, which were horizontally, not vertically aligned. The effective and ineffective squirrel behaviors for retrieving a nut still applied, though all of the levers had nuts.

The squirrels (Arnold, Leonard, Sarah, Simon and Suzy) were lab residents, average age 6 years, with similar experimental histories in cognitive tasks. The researchers had them participate individually in a series of trials that began when the squirrel touched the box; it ended when the squirrel obtained all the nuts or specified times had elapsed.

Squirrel Performance
Encountering a new stimulus, the squirrels took on the order of 23 seconds to make contact in the first trial with the new puzzle box, compared to about 11 seconds in the last trial with the original puzzle box.

Once they got started, however, the squirrels needed about half the time to retrieve nuts in the first trial with the new puzzle box than they did in the first trial with the original box (2 sec versus 4 sec) and only about 1 second more than they needed in the last trial with the original box.

The researchers used video to analyze four behavioral traits: persistence (rate of attempts), selectivity (proportion of effective behaviors), motor diversity (rate of trying different tactics) and flexibility (rate of switching tactics after a failed attempt).

All squirrels demonstrated a high proportion of effective behaviors, reflecting the interaction between memory and behavioral traits for problem-solving. Remembering task-effective tactics, they consistently changed from ineffective to effective behaviors after failed attempts.

Wrap Up
Now that the role of memory in the problem-solving ability of squirrels (at least five) has been addressed, it’s appropriate to ask: Do squirrels find the nuts they hoard?

Here, the findings are mixed. I’ve seen comments about studies that show squirrels fail to recover most of the nuts they bury, but I haven’t seen those studies. In contrast, small sample, controlled studies I’ve reviewed had the opposite results. One article posited that just because a squirrel hasn’t retrieved a nut doesn’t mean that it won’t.

Perhaps the answer is muddied by the generally agreed findings that squirrels repeatedly rebury nuts to deter thieves and pretend to bury a nut to deceive onlookers. They’re pretty smart. Thanks for stopping by.

P.S.
University of Exeter study in Animal Cognition journal: link.springer.com/article/10.1007%2Fs10071-017-1113-7
Article on study on ScienceDaily website: www.sciencedaily.com/releases/2017/07/170713154843.htm
Example studies and articles on squirrels’ ability to locate hoarded nuts:
- www.sciencedirect.com/science/article/pii/S0003347205805068?via%3Dihub
- www.sciencedirect.com/science/article/pii/S000334729690528X?via%3Dihub
- animals.mom.me/smart-squirrel-6321.html
- www.nytimes.com/1994/12/11/nyregion/cuttings-now-it-can-be-told-all-about-squirrels-and-nuts.html
- en.wikipedia.org/wiki/Eastern_gray_squirrel

Visual Perception

Welcome back. Though hardly a visionary, I’ve blogged about stereovision, depth perception, pupil size and, stretching it, eyespots. I’ve got one more.
 
Have you ever seen birds chasing one another? They never slam into a tree branch or feeder. Their visual systems respond fast enough for them to see what’s coming. Luke Skywalker and Princess Leia may have chased scout troopers through the woods on speeder bikes that can go 300 mph, but could you do that without smashing into a tree? 

It goes further, of course. If I see a cat chasing a squirrel, the cat is almost a blur. But the escaping squirrel’s visual system perceives the cat to be moving pretty slowly. 

Video that gives an idea of how squirrels see cats
moving. www.youtube.com/watch?v=J1vpB6h3ek4

If I may continue with cinema, Neo’s visual perception allowed him to dodge and watch bullets fly by. Don’t try it. He’s The One; you’re not.

New research from Ireland’s Trinity College Dublin and Scotland’s Edinburgh and St. Andrews universities suggests that there’s an order to all this. In the animal kingdom, at least among vertebrates, it appears that temporal resolution of visual systems--how well a species perceives time-changing information--is generally related to body size and metabolic rate.

Critical Flicker Fusion Frequency

Using data from the literature, the collaborators conducted a comparative analysis of the visual system temporal resolution of 34 vertebrate species together with mass-specific metabolic rate and body mass. They also added data on brain mass for 28 of the species.

For their measure of temporal resolution, the investigators used maximum values of critical flicker fusion frequency (aka flicker fusion threshold, flicker fusion frequency, flicker fusion rate and the like).

Think of switching a light on and off, faster and faster, until it’s fast enough that the light appears to stay on. The frequency of light ons and offs per second when the light first appears to be on continuously to the observer--whether the observer is a human, squirrel, bird or cat--is the critical flicker fusion frequency. That frequency is dependent on a number of factors, including light brightness.

Vertebrate Scale

The analysis discovered a pattern of visual system temporal resolution that increased with metabolic rate and decreased with body mass.

Small animals with high mass specific metabolic rates in high light environments had the highest maximum flicker fusion frequencies and thus the greatest ability to perceive visually dynamic information. In contrast, large animals with low metabolic rates in low light environments had the lowest flicker fusion frequencies.

The frequencies, measured in cycles per second or Hertz, ranged from European eels at 14 to gold-mantled ground squirrels at 120, with humans checking in at 60. Cat lovers will be aghast to learn that the temporal resolution of their whiz-by cat is only 55, much less than that of dogs, 80, chickens, 87, or pigeons, 100.

Wrap Up

The researchers point out the study’s implications for the evolution of predator-prey interactions as well as less obvious possible influences on ecological niche. But if just learning that littler creatures perceive dynamic information faster than bigger creatures doesn’t impress you, at least recognize that when it comes to how fast you or I can go safely with or without a Star Wars speeder bike, it’s not as fast as pigeons--or, if pressed, chickens. Thanks for stopping by.

P.S.

- Study paper in Animal Behaviour:  www.sciencedirect.com/science/article/pii/S0003347213003060
- Articles on the study on Popular Science and the BBC News websites:
www.popsci.com/science/article/2013-09/small-animals-see-world-slow-motion 
www.bbc.co.uk/news/science-environment-24078179
- Background on flicker fusion frequency:
en.wikipedia.org/wiki/Flicker_fusion_threshold
- Examples of earlier research on flicker fusion frequency measurements:
insects (1958): www.sciencedirect.com/science/article/pii/002219105890012X
cats (1975): www.sciencedirect.com/science/article/pii/0042698975903028
dogs (1989): www.sciencedirect.com/science/article/pii/0031938489900929

Lawn, Garden & Squirrels Photo Addendum

I mentioned Vicki’s attempts to keep squirrels from the birdseed. It got serious when she bought a guaranteed-to-work device that delayed the squirrels’ feeding for possibly an hour.
 

Squirrel on squirrel-proof bird feeder.

Squirrel defeating squirrel-proof bird feeder.

Next, Vicki erected (and painted) a tall, smooth tube on our deck and hung different feeders (and faux vegetation) from its top. (Patent is not pending.)

Was it fear of jumping, missing and falling that restrained the squirrels, or were they just laughing too hard? Whatever it was, it worked for a couple of days. That’s a record!

Vicki's home-made squirrel-proof bird feeder.

Squirrel defeating Vicki's home-made squirrel-proof bird feeder.