Dietary resource preference of the southern flying squirrel (Glaucomys volans).
Southern flying squirrels are an omnivorous species with their diet containing nuts and acorns, in addition to young buds, fruits, fungi, and even carrion and birds eggs (Dolan and Carter, 1977; Saunders, 1988; Harlow and Doyle, 1990; Thomas and Weigl, 1998; Thorington and Ferrell, 2006). Experimental studies have been conducted on the bioenergetics (Pearson, 1947) and foraging behavior of the Southern flying squirrel (Thomas and Weigl, 1998). Stapp (1992) also reported Southern flying squirrels have a low metabolic rate, especially compared to diurnal tree squirrels and other mammals of similar body mass. Thomas and Weigl (1998) found that temperature influences the foraging behavior of G. volans. Below -10 C, the hickory nut Carya spp. was considered the optimal food for Southern flying squirrels due to its high caloric value; whereas above this temperature, their energy needs were met by a diet of acorns. Southern flying squirrels have a dynamic foraging strategy, consuming acorns in autumn and storing hickory nuts for winter, thus optimizing their food resources (Thomas and Weigl, 1998).
There is a dearth of literature, concerning the dietary resource preference and rate of ingestion of G. volans. This study was designed to quantify the caloric input and dietary ranking regarding food resources consumed by G. volans. We selected five food resources based on reported food preferences in the diet of Southern flying squirrels (Sollberger, 1940; Thomas and Weigl, 1998). These food resources were flowering dogwood Comus Jlorida, water oak Quercus nigra, white oak Q. alba, black oak 0. velutina, and pignut hickory Carya glabra', caloric values are summarized in Table 1. We hypothesized that white oak and water oak acorns would rank highest in food preference due to their seasonal abundance and minimal effort required to forage, open, and consume the acorn. Thomas and Weigl (1998) demonstrated that flying squirrels are likely to eat and store the nuts of Carya spp. during winter due to their high caloric value. Unlike the study of Thomas and Weigl (1998), temperature was not a factor in this study; each Southern flying squirrel was maintained at 21 C. We hypothesized that without the factor of cold temperature, Southern flying squirrels would consume acorns rather than the nuts of the pignut hickory, which are characterized by a hard pericarp that is difficult to open and require more energy to process and consume.
MATERIALS AND METHODS
The study was conducted from Nov. 2011 through Mar. 2012 at the HorseShoe Bend (HSB) Ecology Experimental Research Site located within Clarke County, in proximity to Athens, Georgia (33[degrees]56'3"N, 83[degrees] 21'31"W). Five types of food resources were collected during autumn 2011 and refrigerated at 2 C prior to feeding. These include: flowering dogwood, water oak, white oak, black oak, and pignut hickory. Twelve adult Southern flying squirrels (8 males, 4 females) were livetrapped at HSB. Individuals were weighed to the nearest gram and ear tagged for identification. Each individual was housed in a temperature-controlled 21 C cylindrical tank that functioned as an experimental mesocosm for this study. Each tank measured 80 cm in diameter and 88 cm in depth, and was covered by a sturdy mesh wire lid to prevent escape. A nest box, containing nonabsorbent cotton and supporting an attached outside water bottle, was placed in the center of each tank. Each Southern flying squirrel was acclimated to its tank for 1-2 d. Five food bowls, each containing weighed portions (30 g) of each food type were placed along the circumference of the tank 72[degrees] apart from the central nest box. We computed rate of ingestion energy by weighing each food type, then determined non-consumed food the following day. Each food bowl was then refilled, weighed, and placed back in the tank. We repeated this process for five consecutive days for each individual. Rates of ingestion were expressed as Kcal x g live [wt.sup.-1] x [d.sup.-1]. Each Southern flying squirrel was weighed to the nearest gram at the beginning and upon termination of the feeding process. Individuals were then released at the site of capture. Animals were handled in accordance with the guidelines approved by the American Society of Mammalogists (Sikes et al., 2011), and The University of Georgia Animal Care and Use Committee (AUP #A 2010 7-116).
A split-plot Analysis of Variance (ANOVA) was used to compare the differences in diet preference among individuals and between sexes. An Analysis of Covariance (ANCOVA) was used to compare weight to amount of food eaten. A Tukey-Kramer test was used to determine pair- wise differences among diets. The statistical software used was SAS 9.2. Significant differences were determined at an [alpha] level of P [less than or equal to] 0.05.
The mean daily rate of ingestion for G. volans was 1.87 ([+ or -] 0.06 se) Kcal x g live [wt.sup.-1] x [d.sup.-1]. The preferred diet of the Southern flying squirrel was white oak acorns with 0.93 ([+ or -] 0.14 se) Kcal x g live [wt.sup.-1] x [d.sup.-1] (Fig. 1). The subsequent preferences were black oak and water oak acorns with mean rates of ingestion 0.31 ([+ or -] 0.08 se) and 0.30 ([+ or -] 0.04 se) Kcal x g live [wt.sup.-1] x [d.sup.-1], respectively. The least preferred food types were pignut hickory nuts and flowering dogwood fruits with mean rates of ingestion 0.16 ([+ or -] 0.02 se) and 0.14 ([+ or -] 0.04 se) Kcal x g live [wt.sup.-1] x [d.sup.-1], respectively. Energy consumption varied significantly according to food type ([[F.sub.4,44] = 24.91, P < 0.001); energy consumption of white oak was significantly higher than all other food types, and pignut hickory significantly lower than other food types except flowering dogwood. Sex itself did not significantly predict caloric intake ([F.sub.1,10] = 3.57, P = 0.088), and additionally, there was no significant interaction of sex and food preference when predicting caloric intake ([F.sub.,440] = 0.06, P = 0.994). The lack of this interaction indicates that male and female food preferences, gauged by caloric intake, are similar. A highly significant effect was found when comparing weight per individual with daily caloric intake ([F.sub.1,44] = 6.81, P = 0.012).
We hypothesized that white oak and water oak acorns would rank highest in food preference due to seasonal abundance and minimal effort required to collect and consume these acorns. White oak indeed was the preferred diet of the Southern flying squirrel when the temperature was maintained at 21 C; energy consumption of white oak acorns was significantly higher than other food types. We determined the mean daily ingestion rate of the Southern flying squirrel is 1.87 ([+ or -] 0.06 SE) Kcal x g live [wt.sup.-1] x [d.sup.-1], thus white oak composes 49.7% of the Southern flying squirrel average daily diet given the available food resources. The next preferred foods of the Southern flying squirrel were acorns of the black oak and water oak, and the least preferred foods of the Southern flying squirrel were fruits of the flowering dogwood and nuts of the pignut hickory.
Our study substantiates the findings of Thomas and Weigl (1998); we noted a dynamic foraging strategy of G. volans while observing individual Southern flying squirrels throughout the duration of the study. Most Southern flying squirrels opted to consume white oak acorns, but mainly stored black oak acorns and pignut hickory nuts within their nest boxes inside each mesocosm tank. These uneaten nuts, including pericarps, were not considered consumed foods during daily diet computations. The fact that individuals cached acorns and nuts in their nest boxes indicates that these diets were to serve as food resources in later months when there is a scarcity of white oak acorns. The storing of pignut hickory nuts indicates that during winter months the advantages of the high caloric value of pignut hickory 7.97 ([+ or -] 0.33 SD) Real x g dry [wt.sup.-1] outweighs the disadvantages of the difficult to open pericarp of the nut. Given the option, Southern flying squirrels will not immediately consume pignut hickory nuts, but store them for consumption at a later date.
The rates of ingestion interaction between sex and food preference were not significant, suggesting that males and females do not differ in food preferences. The sample size (8 males, 4 females) could have influenced the ability to detect significant differences. It also is possible that a wild population might have different rates of ingestion during this time. There was no significant difference between males and females regarding caloric intake. We did find that as Southern flying squirrels increase in weight, they consume significantly less energy per gram live weight. We theorized this relationship could be due to a bioenergetic strategy of caloric intake in order to limit weight gain in adult Southern flying squirrels. Because gliding is essential to the daily activities of the Southern flying squirrel (Barrett el al., 2009), it is possible that deviating from a weight threshold could negatively impact gliding ability, thus decreasing individual survivorship. This finding invites future research, such as the testing of differences in food preference of the Southern flying squirrel according to their latitudinal location within their geographical range, as discussed by Thomas and Weigl (1998).
Acknowledgments.--We thank E. Froetschel, D. Gaydos, R. LoPilato, J. Moree, and A. Penn for fieldwork and laboratory assistance at HSB. We thank K. Love-Myers, Associate Director of the Statistical Consulting Center, University of Georgia, for assistance in data analysis. This study was supported in part by funding from the Eugene P. Odum Endowed Chair in Ecology held by G. W. B.
Barrett, G. W., S. Shivers, K. Meek, and M. Shuman. 2009. Home range of the Southern flying squirrel (Glaucomys volans) in a forested riparian peninsula. Georgia J. Sci., 67:19-24.
Burns, T. A. and C. E. Veirs, Jr. 1973. Caloric and moisture content values of selected fruits and mast. J. Wildlife Manage., 37:585-587.
Dolan, P. G. and D. C. Carter. 1977. Glaucomys volans. Mammal. Spec., 78:1-6.
Gibbes, L. A. and G. W. Barrett. 2011. Diet resource portioning between the golden mouse (Ochrotomys nuttalli) and the white-footed mouse (Peromyscus leucopus). Am. Midi. Nat., 166:139-146.
Harlow, R. F. and A. T. Doyle. 1990. Food habits of Southern flying squirrels (Glaucomys volans) collected from red-cockaded woodpecker (Picoides borealis) colonies in South Carolina. Am. Midi. Nat., 124:187-191.
Pearson, O. 1947. The rate of metabolism of some small mammals. Ecology, 28:127- 145.
Saunders, D. A. 1988. Southern flying squirrel, p. 95-97. In: D. A. Saunders (ed.). Adirondack mammals.
State University of New York, College of Environmental Science and Forestry, Syracuse, New York. 216 p.
Sikes, A. S., W. L. Gannon, and The Animal. Care and Use Committee. 2011. Guidelines of the American Society of Mammalogists for the use of wild mammals in research. J. Mammal., 92:235-253.
Sollberger, D. E. 1940. Notes on the life history of the small eastern flying squirrel. J. Mammal., 21:282-293.
Stapp, P. 1992. Energetic influences on the life history of Glaucomys volans. J. Mammal, 73:914-920.
Thomas, R. B. and P. D. Weigl. 1998. Dynamic foraging behavior in the Southern flying squirrel (Glaucomys volans): the test of a model. Am. Midi. Nat., 140:264-270.
Thorington, Jr., R. W. and K. Ferrell. 2006. Squirrels: the animal answer guide. Johns Hopkins University Press, Baltimore. 183 p.
KATHERINE R. HELMICK (1), TERRY L. BARRETT, and GARYW. BARRETT, Eugene P. Odum School of Ecology, University of Georgia, Athens 30602. Submitted 7 May 2012; Accepted 15 November 2013.
(1) Corresponding author: e-mail: firstname.lastname@example.org
Table 1.--Summary of caloric values (Kcal x g dry [wt.sup.-1] [+ or -] sn) for each food type collected from the Georgia Piedmont based on five samples per diet. Acorns and hickory nuts are minus pericarp Food type Caloric value (Kcal x g dry [wt.sup.-1] [+ or -] sd) Carya glabra 7.97 [+ or -] 0.33 Comus florida 5.36 [+ or -] 0.12 Quercus velutina 5.21 [+ or -] 0.13 Quercus nigra 5.20 [+ or -] 0.17 Quercus alba 3.91 [+ or -] 0.03 (a) Caloric value from Burns and Veirs 1973, Gibbes and Barrett 2011
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|Title Annotation:||Notes and Discussion|
|Author:||Helmick, Katherine R.; Barrett, Terry L.; Barrett, Gary W.|
|Publication:||The American Midland Naturalist|
|Date:||Feb 1, 2014|
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