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!