Bryan Hummel

                                                                                                            Ecology 3434

                                                                                                            Ribble; 8:30 TR

                                                                                                            February 23, 1999.

 

Fox Squirrel Foraging Habits at Trinity University

 

Introduction:

            An experiment was carried out to test the predation risks on Fox Squirrels (Sciurus niger) during forging on a college campus.  The results were expected to show that there was little risk of predation on the campus.

 

Methods:

            Each of 5 students made 4 feeders with 100 grams of sand covering 50 grams of sunflower seeds.  The feeders were placed in different areas around campus.  One tray was placed next to the trunk of a tree (near) and the second was placed at a distance of 10 meters (far).  The third and fourth were done in a similar fashion, one near and the other far.  The trays were then left alone for several hours (2.5 hours to 5 hours).  At the end of this time, the trays were collected, the sand was screened out and the remaining intact seeds were weighed to determine the amount of seeds consumed.

 

Results:

            The seed consumption at each feeder was recorded in Table 1.  The total amount of seeds consumed was 51.4 grams for the trays placed near the trees and 58.5 grams for the trays that were 10 meters away.  Because the standard deviations were 4.8 and 4.9 respectively, there is an overlap in the possible values.  Table 1 also shows that there were 4 sites where there were no seeds consumed.

 

 

Weight of seeds left (grams)

Weight of seeds consumed (grams)

 

        Near

         Far

        Near

        Far

 

Bryan

42

45

8

5

 

 

44

44

6

6

 

Jennifer

47.5

48

2.5

2

 

 

47

44

3

6

 

Matt

38.1

37

11.9

13

 

 

36

40

14

10

 

Libby

50

36.5

0

13.5

 

 

50

50

0

0

 

Vanessa

46

50

4

0

 

 

48

47

2

3

 

TOTALS

448.6

441.5

51.4

58.5

 

Average

44.86

44.15

5.14

5.85

 

Standard Deviation

 

4.815069

4.933164

 

 

Table 1.

            Table 1 compiles the experimental data into the first two columns.  The weight of seeds consumed was calculated, as well as the totals for all 4 columns.  The average and standard deviation were also calculated.

 

Discussion:

            Evaluation of Table 1 shows us that there was no significant difference between the feeders placed near the trees and the trays placed at a distance.  Assuming that the seeds were eaten by squirrels and not by birds, this confirms our hypothesis that the predation risk on the squirrels would be minimal.  At a college campus there are several factors that would decrease the effects of predation.  First, the campus is very well maintained and always traversed with humans, which makes for an undesirable habitat for most natural small animal predators.  The lack of predators over several generations of squirrels would decrease the squirrels concern of predation.  The abundance of humans at all hours of the day and night would also have an effect on the squirrels.  The squirrels would grow accustomed to people walking by, and thus they would not feel threatened by the humans who walk by during their feeding.

            There was a difference in the number of grams consumed at the near feeders as compared to the farther feeders even though the difference was deemed insignificant by the standard deviations.  The standard deviations in this experiment are not absolute because they could be changed with several factors such as number of feeders or length of time the feeders were available.  To explain the difference we can look at other factors besides predation.  Predation is just one variable in the squirrels decision to stay and eat or to leave in retreat.  We can use an equation that relates the rate of food harvest (H), the energetic costs of finding and handling the food (E), the cost of missed opportunities (M), as well as the risk of predation (P). This can be written as H > E + M + P, meaning as long as the benefits of the harvest (H) outweigh the costs of the harvest, the squirrel should stay and eat until the benefits lower or the costs rise. The food consumption with the harvest and the missed opportunities are constant because of the amount of food per tray is constant, thus we must look at the energetic costs and predation.  Since predation is most likely of little importance on a college campus, the focus will fall on the energetic costs of finding and handling the food.  Since squirrels spend a great deal of their time in trees, it seems reasonable that they would find the feeders close to the trunk before finding the ones further away from the trunk.  The handling time of actually splitting and eating the seeds should be constant at either spot, so the difference could be attributed to actually finding the feeders.  There may still be an effect by predators such as cats, but most of the cats are shy and they do not hang around during the day.  I would assume that the difference in consumption between near and far is because of the energy used to find the feeding trays more than predation, but if the experiment were expanded, the data would surely change and allow for a better comparison.

                                              

Fox Squirrel Foraging Habits at Trinity University

 

Bryan Hummel

Ecology 3434

Ribble; 8:30 TR

February 23, 1999.

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