National Lakeshore Michigan
Scientists can tell a lot about the habitat requirements of an animal by examination of the contents of the digestive tract. In birds, examination of the crop contents is an especially easy method of determination of the diet, because the contents are not yet digested.
In this exercise, ruffed grouse crops are collected from hunters, the contents are analyzed, and hypotheses are made about the preferred habitat of the ruffed grouse (partridge).
Ruffed grouse crops
Plastic Petri plates
Advanced Preparation by Teacher
A week or so before the beginning of ruffed grouse season, prepare a school announcement asking students to save the crop from any grouse that they may shoot. As an incentive, offer a small payment for each crop that is turned in. All crops may be placed in the freezer until they are needed. As well as turning in the crop, students should provide information about the habitat in which the grouse was found.
1. In this activity, students will dissect ruffed grouse crops, and separate identifiable contents into groups.
2. The percent of the total crop contents of each food type is determined.
3. A hypothesis is made regarding the type of habitat that would optimally provide for the food requirements of the ruffed grouse.
1. A grouse crop is distributed to each student or group of students.
2. The crop is opened, and the contents are divided into piles of similar materials, Those bits of food that are unidentifiable are placed in a pile with that name. Descriptions of food types should be named as specifically as possible. For example, clover would be better than just classifying the food as "leaves".
3. Mass the piles of food types in grams.
4. Determine the total mass of food in the crop in grams.
5. Calculate the percentage of the diet comprised by each food type using this formula:
Percentage (%) of diet of a specific food type equals (=) grams of a specific food type times (x) 100 = total grams of food in crop
6. Construct a bar graph with food types along the bottom, and percentage of crop contents along the vertical axis. Use a different color for each food type.
7. On the blackboard, compile the data from all crops, totaling the amounts of specific food types, and determining the total amount of food in each crop. Determine the percentage of diet of each food type; calculate from all of the collected crops.
Record all data in the chart below (you may add more rows if necessary).
1. Comparing the results of the crop you analyzed to the collective results, was your partridge feeding in a habitat that was essentially the same as other partridge, or was it feeding in a different habitat?
2. How would you classify the grouse: herbivore, carnivore, or omnivore?
3. The crop analyses were made in the fall. What specific differences in diet would you expect to find during other seasons of the year?
4. Was there anything in the crop of your partridge that you did not expect to find? If so, what?
5. Based on the results of all of the crops analyzed, propose a hypothesis for the type of habitat where you would expect to find ruffed grouse. Does this agree with the habitat information provided by the hunters?
Gullion, Gordon, 1984, Grouse of the North Shore. Willow Creek Press, Oshkosh, Wisc.