The first few trials — Working out the kinks

After feeding Penelope and Louise only 8 grams/day for 3 days, we have officially begun our experiment investigating whether rats hoard more alone or when placed together. We are currently in the first stage, during which we are doing a number of trials with each rat alone. We choose randomly which rat goes first each day, and we are only able to do one trial per day because the rats have to be the same “amount” of hungry at the start of each trial. We feed them the same amount and at the same time each day, but once they begin eating during each trial, the amount of food they eat is difficult to control and we must wait a day until the next trial.

After 4 trials, Louise has hoarded an average of 7.0 pellets, and eaten an average of 11.5 times. Penelope has hoarded an average of 14.25 pellets, and eaten an average of 8.25 times. However it is important to note that on the first day, Penelope hoarded a shocking 30 pellets before the trial ended (unfortunately we do not have a video of this particular trial.) The number of pellets she has hoarded has been much lower ever since.

We have also observed a marked difference in each rat’s hoarding behavior. Penelope is a “larder” hoarder while Louise is a “scatter” hoarder. Refer to the previous post for a more detailed explanation.

On a different note, after 3+ days of eating only 8 grams a day, both Penelope and Louise showed a marked decrease in body weight. Due to this dramatic weight loss, we decided to increase each rat’s daily food ration to about 14 grams (including what they eat during each trial.) This does not seem to have noticeably affected their hoarding habits.

At this point we are concerned that they are not hoarding as much as they might in a more natural situation; however we believe this could be due to:

1) Research shows that rats tend to hoard less in unfamiliar environments (like the one in which we have placed them.) However, it was also shown that the animals gradually habituate to their environments and hoarding eventually increases to a more natural rate (closer to the number they would hoard in their home cages.) Thus, we hope that the rats will become more comfortable in the tank over the next few trials.

2) The pile of food is too ambiguous. Due to the small size of the tank, the pile of food we provide sometimes becomes interspersed with the food the rats have already hoarded. We are now placing the pellets inside a container ( the bottom of a plastic bottle) which we have placed exactly where we used to place the food.

The rats are not distracted by the new container and willingly take food out of them.

3) We also read that certain animals prefer to hide their food in or under something. We did a trial run with Louise in which we placed a small food container in the corner of the tank, under which she could have hoarded food. Although she played with the container for a couple of minutes, she paid little attention to it otherwise and continued to hoard and eat her food in an opposite corner.

4) We are also slightly concerned that the rats are spending too much time eating, since hoarding consists of “deferred consumption” or handling and keeping the food, but not eating it. Perhaps the rats are too hungry.

5) The rats become very interested in the “leftover” smells of the rat who went first wafting from across the tank. They sniff near the screen for long periods of time, push the screen with their noses, and stand up with their front feet on the screen. We will begin completely washing out the entire tank between each trial.

6) Perhaps the rats aren’t hoarding very much because they have become accustomed to being fed after the experiment is complete for the day. Thus, maybe the don’t think they need to hoard because they know they will get food afterward with very little effort. We will now feed them no earlier than 2 hours after trials have been completed. Maybe this will increase their motivation to hoard!

7) OR maybe rats just don’t hoard very much when they’re alone!

We have posted two videos, one of each rat, to give you an idea of what each rat looks like when she hoards. Enjoy!


October 30, 2008 at 1:55 am Leave a comment

Larder Vs. Scatter Hoarding

We came across an interesting article by Stephen Vander Wall in which he describes two different types of hoarding: lardering and scattering. This is most fascinating because we have observed that Penelope seems to be a larder hoarder while Louise is a scatter hoarder.

Larder hoarding refers to the concentration of all hoarded food in one spot. In other words, the animal goes back and forth between the food source and one particular site. Larder hoards look like recognizable clumps.

Scatter hoarding, on the other hand, means that the hoarded food is not concentrated, rather it is highly dispersed. At its most extreme, only one piece of food is hoarded in each spot. However, it also refers to very small bunches.

Here is a visual comparison of the two types of hoarding:

Penelope–Larder Hoarding


Louise–Scatter Hoarding

October 30, 2008 at 12:27 am Leave a comment

Hoarding Experiment–Trial Run

Today we did a trial run of our hoarding experiment.  We began by first setting up the wire mesh screen that cut down the middle of the glass aquarium, creating two separate halves.

We then broke the large food pellets in half, attempting to make them all relatively the same size.  We created 50 of these.

We made 50 pellets because we plan to count how many pellets are hoarded until either the rats do not hoard for a period of 3 minutes or they hoard up to 50 pellets.  Even though at this point we have no idea how many pellets Louise and Penelope would hoard overall (hence the trial run), we decided to be safe and have at least 50 pellets on hand.

We then placed 5 pellets in a pile on the left side of the wire mesh. Once the rat has hoarded the 5th pellet, we will add 5 more pellets, repeating this until 50 pellets have been hoarded or 3 minutes have elapsed since the last hoarded pellet. We also plan on weighing the pellets before and after each trial in order to keep track of how much food is eaten.  Here is a picture of the pellet set up:

After this was set up, we put Penelope into the aquarium and watched what she did.  The trial was not a very big success! Here is a video of what Penelope did:

As you can see, Penelope picked up a pellet and ran around with it, but never actually dropped it.  She also eventually pushed through the wire mesh barrier. We have come up with a number of solutions:

1) We need to remedy the un-sturdy mesh barrier problem.  We are looking to weigh the bottom down with a piece of wood, which may also allow us to wedge it in and make it unmoveable.  If this doesn’t work, we have a Plan B! This will include taking two of the metal drawers (like the ones they live in now) and placing them next to each other in such a way that the metal grated sides are touching.  Thus, they have two separate areas but can still see and smell each other.

The only problem we saw here is that they can easily jump out of these boxes; however, all we need is some sort of see through covering to place over each drawer.

2) We are positive that the rats need to be much hungrier.  We have switched them to a diet of only 8 grams per day.  We will do this for 3 days and try our experiment again on Friday.  This will also give us time to figure out which box/tank we will use, gather our supplies, and allow the rats to become familiar with the new environments.

October 23, 2008 at 3:53 pm Leave a comment

Hoarding Experiment Proposal

Hoarding is defined as a behavior in which a rat will remove piece after piece of food, add each to its store in a specific place, and then return for more. Generally we are looking to find out what factors influence the hoarding response of rats. More specifically, we would like to know whether hoarding would increase or decrease in the presence of another rat, rather than when the rat is alone.

There are many other manipulations that could be investigated in relation to their affects on hoarding, and time willing, we hope to be able to explore as many of these as possible. These variables include pellet size, how hungry the rat is, the addition of fear, temperature of the environment, etc. It would also be interesting to look into whether rats would prefer to hide their hoarded food in or under something, and whether the same rat could remember where it had hidden its food over a period of time.


Penelope and Louise will be put on the same feeding schedule for about a week before the experiment begins. They will be fed at the same time with the same amount of food each day, and deprived for the same amount of time before trials. Our apparatus will include one glass aquarium with a removable piece of hardware cloth that will cut the aquarium in half down the middle. The hardware cloth will enable the rats to both see and smell each other. For the beginning trials, each rat will be put into one side of the the split aquarium with a single pile of food. The pile of food will be weighed before we add it to the aquarium so the amount of food stays consistent between both rats. Although there will be no rat placed on the other side of the aquarium for these particular trials, we want to use the divider in order to control for the size of the “hoarding space.” Once the rat is placed in the tank with the food, the number of pellets hoarded and the number of pellets eaten in a five minute period will be recorded. We will count hoarding as any movement of the pellets to a consistent area. Furthermore, the pile of food will already be in the aquarium before the rat is added.

The next set of trials will again include dividing the aquarium in half with the hardware cloth; however, this time both rats will be involved. There will also be two piles of food, one on each side of the glass. The food will be placed in such a way that the rats are facing each other. Each rat will be placed on one side of the aquarium with the hardware cloth dividing the two rats. The number of pellets each rat hoards and the number of pellets each rat eats in five minutes will once again be recorded.

Finally, the last set of trials will include the aquarium without the divider. One pile of food will be placed in the aquarium. This pile will be the equivalent of the combination of each rat’s individual pile (i.e., an individual rat pile x2.) Both rats will be placed in the aquarium at the same time (undivided) and the number of pellets hoarded and eaten by each rat in a five minute period will be recorded. Once this task is completed, we will include an additional stage in which both rats are put into the aquarium without the divider; however, in this case there will be two individual piles of food. We will again record the number of pellets hoarded and eaten by each rat.

If time allows, further tests of the affects of additional variables on hoarding will be examined. One such test includes manipulating how hungry the rat is and repeating the above procedures. The rats will be tested after 12 hours without food, 24 hours without food, and immediately after being fed their daily ration (complete satiation.) Another potential manipulation is to add boxes, tubes, or pieces of cloth to the aquarium to see if the rats hide their food or simply hoard in an open space. Once the rats have hoarded, they will be removed from the aquarium for a single day. Upon being placed back into the aquarium, we will observe whether the rats show recall of their particular “hoarding spot” by returning to the area in which they had hoarded their food the previous day.

October 19, 2008 at 10:59 pm Leave a comment

Louise’s Trick cont…

As I mentioned in a previous post, I decided to change Louise’s trick from teaching her to jump over an obstacle (ruler) to trying to get her to “beg” on her two hind feet at the word “up.” Since Louise stands up so much on her own, all I had to do was capture the behavior by clicking and feeding her as soon as both of her front feet left the ground. I also tried to coax her by holding a piece of food over her head. Thus, I often just gave her the food directly from my hand; however, I also intermittently delivered the food through the tube in the food corner.

I then began adding the “up” command on the very first day of training. I say “up” right before it looks (to me) like she’s about to stand on her hind feet. However, I’m often wrong in my assumption and end up saying it a bunch of time before she actually stands up. As of now, she still is not showing much response to the “up” command. I’m hoping if I just continue to do it over and over, she’ll eventually begin to stand up on command, but at this point I think she is just so interested in the food that I’m holding over her head that the “up” command has little salience. I’ll continue to work on not holding the food to coax her to stand up, and only reinforcing her through the tube in the food corner. We’ll see where that gets us!

Here is a brief video showing the different ways I reinforced Louise, as well as what the trick is supposed to look like!

I will continue to work with Louise as much as possible.  However, Erika and I will be starting in on our experiment as soon as possible, so trick training time may be limited!

October 12, 2008 at 3:59 pm Leave a comment


After clicker training our next assignment was having our rat do a trick. I have been working this past week with Penelope to go through a tunnel, which is a plastic cup. I took a solo cup and cut the bottom out of it. I tapped it to the floor of the aquarium. I have been shaping Penelope to go through the cup and I think she has it. At the beginning of introducing this trick Penelope was very distracted by the cup. The first time I tried to train with her, I got nothing accomplished because she was seemed to be too interested in jumping on the cup, trying to chew the cup and rip it off from the floor. The first step in shaping that I did was when she put her head in the cup I clicked. Once she got use to this the next step was half her body in the cup. In this video you can see her standing on the cup and her first stages of shaping.

After a week of practice and shaping Penelope is completely going through the cup now. Here is a video showing off her new trick!!  

October 5, 2008 at 9:24 pm Leave a comment

Louise’s Trick

On Thursday I began trying to teach Louise her first trick: jumping over a piece of wood (aka, a ruler.)  I began by simply letting her go up to the ruler to sniff and clicking which she touched the ruler.  I had planned on gradually clicking when she put her feet on it, then when she put her head over it, and then when she put her feet on the other side, but Louise was ten steps ahead of me and just began jumping over the ruler without much coaxing.

I had been placing a small piece of food on the other side of the ruler, and once she jumped I would click and she would find the food.  This seemed to be working well and Louise continually jumped over the ruler, until she simply…stopped.  For a couple of days I couldn’t get Louise to jump over the ruler without some sort of coaxing (holding the food in my hand and luring her over, or just giving her a nudge.)  With some help she started jumping again, but she then seemed to become very overstimulated by the reappearance of my hand in the tank.

I believe she also was slightly confused by the fact that she had to jump over the ruler in two different directions, especially when one direction pointed her toward her usual food corner and the other didn’t.  Also, since I began teaching the trick with a ruler that stretched the entire way across the tank, after I clicked, she would try to jump back over the ruler to get back to the food corner, which was just too complex for the both of us!

Thus, I’ve decided to try a different, simpler trick.  Today I am going to try to teach her simply to do a “begging” stance in which she stands on her back legs to the command “up.”  I was hesitant to do this at first because she so often stands on her back legs and sniffs when she’s off task, but I think it is a much simpler trick for not only her first time learning, but my first time teaching.  We’ll see how it goes!

October 5, 2008 at 7:24 pm Leave a comment

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