It looks like we’ve hit a home run! After a lot of struggling, problem solving, and changing different aspects of our experiment, we have finally managed to get the rats hoarding again. To review, we began our experiment hoping to discover whether rats hoard more pellets when alone or when they are together, but we ran into a problem when the rats were only averaging about 7 pellets per trial. Thus, we set off to answer the question of WHY the rats were no longer hoarding. Over the course of a couple of weeks we researched hoarding and changed the following things, hoping they would make a difference and increase the number of pellets each rat hoarded:
1) Placed the pellets in a container rather than in a pile on the ground
2) Delivered the pellets one by one by hand instead of in a pile
3) Varied the size of the pellets
4) Fed them before each trial to ensure they were no longer hungry (versus depriving them)
5)Took away hoarded food to motivate them to hoard more
6) Gave them free reign of the whole tank (more space)
Unfortunately, NONE of these manipulations worked. What DID work was the addition of a familiar washcloth and “cubby” (both concepts are described in previous posts) into the experimental tank, along with a slightly redesigned apparatus (which is also described in previous posts.) From research we learned that rats tend to hoard more in their own cage, and a larger space is more representative of a rat’s natural environment.
Thus, we have begun collecting data in hopes of pursuing our original proposal for the remainder of the semester. After 3 trials, Louise has hoarded an average of 34.33 pellets, and Penelope has hoarded an average of 29.0 pellets. You can see in the following graph that this is a vast difference from previous trials!
This graph shows the change in Penelope’s hoarding behavior between the old apparatus and the new apparatus.
This graph shows the change in Louise’s hoarding behavior between the old appartus and the new apparatus.
In the following video, you can see Penelope’s great hoarding technique! This consistent back and forth movement between the food pile and her box is a huge difference from previous trials.
We will continue with “alone” trials for the next week, and then switch to trials in which Penelope and Louise are in the tank together, separated by the wire mesh divider. We will stick with the following small changes:
1) We will stop counting the number of times each rat takes a bite of a pellet. Instead we will keep track of how many grams each rat eats.
2) Instead of ending each trial after 3 minutes of non-hoarding or up to 50 pellets hoarded, we will make each trial 25 minutes long or up to 50 pellets hoarded. We noticed that at times the rats would become distracted for a few minutes (standing on their hind legs, sniffing, jumping on their boxes, etc.) but then continue hoarding. Thus, we felt it was appropriate to wait and give the rats the opportunity to hoard even more pellets. Here is a video of Penelope NOT hoarding (due to distraction behaviors) in the beginning, and then getting “re-focused” and starting to hoard again:
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