Effects of Climatic Changes on the Foraging Behavior of Fox Squirrels (sciurus niger) Bradly M. Hussey

Transcription

1 Hussey: 1 Effects of Climatic Changes on the Foraging Behavior of Fox Squirrels (sciurus niger) Bradly M. Hussey Grand Valley State University Department of Biology, Allendale, MI, Submitted: Monday, 12 April, 1999 (991) Keywords: Ethogram, Fox Squirrels, Tree Squirrels, Foraging Behavior, Climate, Temperature, Behavioral Patterns.

2 Hussey: 2 Introduction The fox squirrel (Sciurus niger), like all other living organisms, must intake a specific minimum amount of food per day in order to sustain life. In more recent years, as the ever increasing human population continues to grow, the fox squirrel has been losing its natural woodland habitat to residential and commercial expansion efforts. This increase in human habitat has, in a sense, left the fox squirrel without a large enough foraging area to sustain himself except in rural areas. (Gurnell & Pepper, 1993) Thus, the squirrels living in urban and suburban areas have become reliant on the generosity of their human neighbors to obtain their food. (Haverna & Nixon, 1980) What we wanted to know was whether squirrels were more or less dependent on human aid during the colder seasons of the year. Our hypothesis is that squirrels will eat more human aid food during the warmer seasons than in the cooler seasons. Because fox squirrels are much more active in warmer weather, their caloric intake will have to rise to keep up with their increased energy needs. (Gurnell, 1996)(Pauls, 1978) However, other factors may play a role in the displayed behavior. For example, fox squirrels mate in the early spring. Thus, the female squirrel, in order to prepare for the energy requirements of the baby as well as her own, may greatly increase her food intake. (Ferron, 1986) The five fox squirrels studied in this experiment, although wild, have been under the care of an elderly lady for 4 years. They have been fed bread, corn, seed and water every morning at promptly 9 a.m. and then again at 2 p.m. All of

3 Hussey: 3 the squirrels visit the feeding site every day. Hence, it can be assumed that the population of fox squirrels is reliant on the elderly lady for their food. (Sullivan, 1990)(Klenner & Krebs 1991) The squirrels are all believed to be related with two being parents, one female offspring and two male offspring. Methods This study was conducted in Kentwood, Michigan. A West-facing, second story, natural oak deck was used as the study area. The deck measures 7.2 meters by 4.5 meters, and is covered from direct sunlight by an overhang of equal size. Data were collected from 12 p.m. to 5 p.m. on every Saturday and Sunday from 13 March, 1999 through 3 April, The ambient air temperature was taken each day at 12 p.m. and recorded (NWS). The weather conditions were also recorded. Each slice of bread in a loaf had the crust removed and was cut into six pieces of equal size. Next, the bread was weighed using a MasterChef digital scale. The bread was then thrown onto the surface of the deck with no attention paid to the assortment of the pieces. The squirrels were also given a fresh supply of water using a two liter refillable squirrel water fountain manufactured by Wild Stuff in Traverse City, Michigan. At the end of each five hour observation period, the uneaten bread was removed from the deck and the weight was taken again. The weight of the uneaten bread was then subtracted from the total weight of the bread put out

4 Hussey: 4 side. This gives us the weight of the bread eaten. This number was also recorded in the data chart. When the study was complete, we entered the raw data into a Microsoft Excel97 spreadsheet. The chart wizard was then used to create a graph for visual inspection. Linear regression of the points was performed using Microsoft Excel97. Unfortunately, the data collected in this study is only open to observational analysis, as statistical analysis would fail to yield any valid results. Results It was determined from this experiment that fox squirrels do vary their food consumption with changes in temperature. There appears to be an inverse relationship between rise in temperature and grams of food eaten (fig. 1). Thus our original hypothesis, that food consumption will increase in warmer weather, is rejected. Linear regression of the points on an x-y scatter plot of the data yields the equation y = x where x, the independent variable, is the temperature in degrees Fahrenheit and y, the dependent variable, is the number of grams of bread consumed by the squirrel population. This equation produces a R 2 value of

5 Hussey: 5 Discussion This population of fox squirrels does not increase their food consumption when the ambient air temperature gets warmer. In fact, our study reveals that the exact opposite happens. This was very puzzling at first. Logic dictates that the squirrels need more energy in order to be more active in the warmer weather. In order for the squirrel to have more available energy, it has to ingest and process more food. However, there are some possible reasons for this change in behavior. First, the squirrels may have chosen a different feeding ground when the weather became warmer. Secondly, the squirrels may have decreased their food consumption because of a decrease in energy needs. During colder weather, it is easy to see that the squirrels ate more food. One thing that this study was lacking was any test to determine if there was another location that the squirrels could acquire their food. However, many times we did observe the squirrels foraging for food throughout the yard and not on the deck when the temperatures were above 60 F. If, when the weather was warmer, the squirrels preferred to forage for non human aid food, this would definitely support the data collected in this study. (Rosenzweig, 1999) Another study would have to be conducted in order to verify these results. The second reason that we may have encountered the observations that we did, stem from a decreased energy need. Although the squirrels are markedly more active in warmer seasons (Haverna & Nixon, 1980), there are other factors which may need to be considered. Thermoregulation has a very

6 Hussey: 6 high energy requirement. (Milton, 1994) In the colder seasons, squirrels need to protect themselves from the cold by increasing their metabolic activities to produce heat. This means that they need to intake and process more food than if they were not regulating their temperature. If thermoregulation requires more energy than does the increased activity level found on warmer days, the data we collected would be supported. Another study would need to be preformed to verify this hypothesis. It should be noted that the raw data alone yielded a very low quality of correlation value (R 2 =.742) for the linear regression. On Sunday, 4 April, 1999 the weather was far from ideal. The temperature was 62 F, but it was raining quite heavily. We believe that the weather alone was to blame for the squirrels apparent loss of appetite. Rather than venture out into the storm, they probably decided to stay in their nests, protected from the elements. Because the number of days that readings were taken was quite small, the decision was made to eliminate that day s data from the study to give a more true to life account.

7 Hussey: 7 References Ferron, J., et al. (1986) Spring and summer time budgets and feeding behaviour of the red squirrel (Tamiasciurus hudsonicus). Canadian journal of Zoology. 64: Gurnell, J. (1983) Squirrel numbers and the abundance of tree seeds. Mammal Review. 13: Gurnell, J. (1996) The effects of food availability and winter weather on the dynamics of a grey squirrel populations in southern England. The Journal of Applied Ecology. 33: Gurnell, J. & Pepper, H. (1993) A critical look at conserving the British red squirrel (Sciurus vulgais). Mammal Review. 23: Haverna, S.P. & Nixon, C.M. (1980) Winter feeding of fox and grey squirrels populations. The Journal of Wildlife Management. 44:41-55 Klenner, W. & Krebs, C.J. (1991) Red squirrel population dynamics I. The effect of supplemental food on demography. The Journal of Animal Ecology. 60: Milton, A.S. (1994) Physiological and Pharmacological Advances. Birkhauser. Basel, Switzerland. Pauls, R.W Behavioural strategies relevant to the energy economy of the red squirrel (Tamiasciurus hudsonicus). Canadian Journal of Zoology. 56: Rozenzweig, M.R. (1999) Biological Phycology. Sinauer Assc. Sunderland, Massachusetts. Sullivan, T.P. (1990) Responses of red Squirrel (Tamiasciurus hudsonicus) populations to supplemental food. Journal of Mammalogy. 71:579-90

8 Hussey: 8 Grams of Bread Consumed y = x R 2 = Temperature ( F) Bread (g) Linear (Bread (g)) Figure 1. Graph of the amount of bread consumed by 5 squirrels at different temperatures.

9 Table 1. Raw data collected in our study. Date Temp. Bread (g) Weather 13-Mar Sun 14-Mar Sun 20-Mar Sun 21-Mar Sun 27-Mar Sun 28-Mar Sun 3-Apr Sun 4-Apr N/A N/A Rain Hussey: 9

10 Hussey: 10 Appendix A. Ethogram of the Fox Squirrel (sciurus niger). Behavior Name Allogrooming Autogroom Biting Chewing Cling Crawl Crouch Descending Climb Food Spin Food Spit Grasp Head Wag Hiding Hop Jump Kneading Left Head Rotation Left Scratch Leg Stand Mouth Drop Peeking Reach Rest Retreating Right Head Rotation Right Scratch Search Sitting Behavior Description Picking at another individual with claws and/or teeth. Picking at one's own body with teeth and claws. Elevation of jaw, usually with an object in mouth. Repeated elevation/depression of jaw with an object in mouth. Using hind legs and forepaws to remain stationary on a vertical object. Slow forward walk (see walk) Flexion of hip, knee, and elbow, extension of shoulder with all limbs in contact with the ground. Downward locomotion using repeated flexion and extension of shoulders in opposition. Rotating food items using rapid flexion and extension of the elbow Ejecting food from mouth while eating Flexion of digits around an object (tree) Movement of superior portion of cranium out of the X-axis into the Y-axis and then returning to X-axis and entering -Y-axis. Concealment from view Short jump (see jump) Flexion of hind limbs followed by rapid extension of hind limbs resulting in forward propulsion of subject with little contact with ground. Flexion of shoulder and extension of elbow using both forelimbs in opposition Rotation of cranium towards left shoulder Rapid flexion/extension of the left hip while foot is firmly adducted against the trunk Erect stationary bipedal stance. Depression of Mandible Looking over top of an object with only the portion of the cranium above the lower boundaries of the eyes above the object. Flexion of shoulder/extension of elbow and extension of phalanges. Stationary position with eyes open and no apparent voluntary activity. Changing direction of forward locomotion. Rotation of cranium towards right shoulder Rapid flexion/extension of the right hip while foot is firmly adducted against the trunk Moving head and eyes in all directions Stationary position with only posterior portion of trunk, and posterior limbs in contact with the ground.

11 Hussey: 11 Sleep Appendix A Continued. Sprawl Stare Straddle Stretch Tail Alert Tail Flip Tail Wag Walk Stationary position with eyes closed and no apparent voluntary actions Laying on surface with ventral side in contact and all legs spread out. Looking intently at and object or individual. Sprawl, with legs and arms loosely laying around circumference of tree branch, or railing. Flexion or extension of all joints often accompanied by short, violent muscle spasms. Tail pointing in the plane perpendicular to the ground Distal 1/3 of tail curls over proximal 2/3 of tail Movement of tail out of the X-axis into the Y-axis and then returning to X-axis and entering -Y-axis. Flexion and extension of all four limbs with contact to the ground (in opposition) resulting in forward locomotion.