Rat Predatory Behavior
Purpose:
The purpose of this lab exercise is to describe the behaviors used by rats in their predation on insects, and to describe the importance of learning in the development of this behavior. Given adequate habituation, a high proportion (80-95%) of naive, undeprived rats will attack and consume insect prey within an initial 30 minute trial. The initial predatory attack typically follows repeated physical contact between the insect and the rat, and consists of rapid pursuit and grasping motions with the forepaws, pinning or pouncing on the dorsal side of the insect with the forepaws, and a series of rapid bites to the head and/or anterior thorax. The insect is then picked up, the head bitten off and discarded, and all but the hardest parts of the exoskeleton consumed. This attack is very similar in form to the highly predatory grasshopper mouse (Onychomys leucogaster).
With repeated exposures, kill latencies rapidly decline to 30-120 seconds. This is due primarily to a more rapid initiation of pursuit which requires fewer, then no, contacts between insect and rat.
In this lab exercise, you will be asked to document the sequence of events that leads to insect consumption by rats, and to track rats' latencies to kill insects as a function of repeated exposures to those insects. To do this, you will use the continuous sampling method. Using the data that you collect, you should describe the typical pattern (or fixed action pattern?) of insect killing in our population of rats. Also, you should propose a possible sign stimulus for the initiation of the attack--what is it, after all, that stimulates the rat to make the attack? Base your conjecture on the data that you collect.
Materials Needed:
Methods:
First, spend a few minutes becoming familiar with the ethogram. Test one another on what initials indicate which behaviors. The more you practice this now, the better your data will be later.
Then, place one cricket into the aquarium holding your rat, and note the time on your data sheet. Then, using the ethogram below, record the behaviors that you observe and the time at which they occur over the next half hour or so. Keep in mind that your primary focal animal is the rat, although a few behaviors in the ethogram are the cricket's (chiefly, CCR).
Rat Predation Ethogram:
Anagram |
Behavior Description |
CCR |
Cricket Contacts Rat (any physical contact between cricket and rat initiated by the cricket)--indicate where on the rat's body it is contacted |
PS |
Pursuit of cricket by rat |
RCC |
Rat Contacts Cricket (any physical contact between cricket and rat initiated by the rat)--indicate where on the cricket's body it is contacted |
PN |
Pin or pounce on insect--indicate how insect is pinned down (what paw, for ex. is used?) |
BITE |
As implied. Rat bites insect. Indicate where on its body the insect receives bites. |
PU |
Pick up. Rat picks up insect in mouth or paws. |
DECAP |
Rat bites head off insect. |
EAT |
As implied. Rat eats insect. |
GR |
Groom. Rat grooms self with paws or tongue and teeth. |
S |
Stationary. Rat is remaining in one place. (note that in this ethogram, any locomotion on the rat's part is therefore "PS" or "O"--depending on what kind of locomotion that is) |
O |
Other. Rat does something not on the ethogram. |
Note the time at which your rat finally kills the first cricket. Then, offer it another. Again, make behavioral observations, and note the time at which the rat kills the second cricket. Continue offering crickets until the end of the lab or until your rat seems no longer interested in eating them (i.e. your rat is stuffed!). Make a graph of the time it takes your rat to kill each cricket. Does it decrease over repeated exposures? How about the behaviors that your rat shows in response to the cricket? Do those change over time? What, if anything, does this suggest about your rat's learning to kill crickets?
Notes to Teachers:
In this lab, any of several types of insects can be used. Crickets work well, but so do American cockroaches or other similar critters with active antennae and a not-too-hard exoskeleton. What appears to trigger the rat's consumatory behavior is repeated contact of the insect with the rat's whiskers or tail.
Students sometimes grow impatient waiting for the rats to become stimulated enough to begin to kill the insects. It can help to have a few "experienced" rats ready as backups, just in case.