2011 SOUTHEASTERN NATURALIST 10(3):509–514 Artificial Nest Cavities Designed for Use by Small Mammals Lara L. Catall1, Darcie L. Odom1, Jacqueline T. Bangma1, Terry L. Barrett1, and Gary W. Barrett1,* Abstract - Forty artificial nest cavities, composed of 7.6-cm plastic tubing (20 PVC white and 20 ABS black), were established in a riparian hardwood forest habitat located in the Georgia Piedmont. Nest cavities situated on wooden L-shaped platforms were secured on Quercus nigra (Water Oak) and Q. alba (White Oak) tree trunks 1.5 m from the ground. Peromyscus leucopus (White-footed Mouse) and Ochrotomys nuttalli (Golden Mouse) used these artificial nest cavities during autumn, winter, and spring. White-footed Mice (36 M, 38 F, 7 J) used the black tubes to a significantly greater extent than the white tubes (12 M, 10 F, 0 J) (χ2 = 33.8, df = 1, P ≤ 0.01). In contrast, Golden Mice inhabited the black tubes (3 M, 5 F, 6 J) to the same extent as the white tubes (6 M, 7 F, 0 J) (χ2 = 0.04, df = 1, P > 0.25). Black tube cavities were warmer (2.5 ºC) than white tubes during the winter breeding season, which may partially explain why White-footed Mice, a less social species than Golden Mice, used these artificial nests to a greater extent during winter. Introduction Avian species are attracted to and protected by property owners who provide resources, such as nest boxes, feeders, and water baths, for conservation and recreational purposes. Small mammals, perhaps inhabiting these same forests or managed habitats, are seldom identified or appreciated, perhaps because of factors such as their nocturnal behavior (Wolff and Hurlbutt 1982), or limited food sources (Scarlett 2004) and nest cavities (Wolf and Batzli 2002) provided by property owners. Occupied artificial nest cavities located in proximity to the property owner likely would encourage familiarity with the ecological value attributed to these small-mammal species. Therefore, our purpose was to design an artificial nest cavity appealing to small mammals that could be located within a managed domain. Nest cavities provide sites for reproduction, protection from predators, and a cache site for food (Goundie and Vessey 1986, Rose and Walke 1988). As a possible limiting factor, nest-cavity availability may influence small-mammal population abundance within a forest ecosystem (Brady et al. 2000, Goundie and Vessey 1986, Vessey 1987). Luring small mammals with resources necessary for survival, such as food and shelter, is an appropriate strategy to attract and study small-mammal species (Rodas et al. 2009). The Ochrotomys nuttalli Harlan (Golden Mouse) and Peromyscus leucopus Rafinesque (White-footed Mouse) compete for resources, such as nest cavities, in a three-dimensional forest habitat space that likely impacts population dynamics (Christopher and Barrett 2006). 1 Eugene P. Odum School of Ecology, University of Georgia, 140 East Green Street, Athens, GA 30602. *Corresponding author - gbarrett@uga.edu. 510 Southeastern Naturalist Vol. 10, No. 3 Many studies have focused on the use of nest boxes to record and observe mammalian behavior (Brady et al. 2000, Edwards and Guynn 1995, Wolff and Durr 1986). Mammals have been reported to use nest boxes more frequently than natural cavities (McComb and Noble 1981) during winter months (Nicholson 1941). Because small mammals often reside in nest boxes for long periods of time, the nest box could provide an effective implement for investigating smallmammal behavior and abundance (Lewellen and Vessey 1999). In our study, artificial tube nests composed of plastic, unlike the commonly constructed wooden-house nest box, were designed to simulate natural shelters, such as tree cavities. We question if these artificial nest cavities would lure small mammals, such as the White-footed Mouse and the Golden Mouse, throughout all seasons of the year. Specifically, the objectives of our study were to determine if small mammals would: (1) use this newly designed artificial nest cavity; (2) prefer white or black plastic tube nest cavities; and (3) occupy nest cavities with similar frequency during each season of the year. Study Area This study was conducted at Horseshoe Bend (HSB) Ecology Experimental Site located in Athens-Clarke County, Athens, GA (33º57'N, 83º23'W). HSB is a 14.2-ha riverine peninsula research site created by a meander of the North Oconee River. This site is composed of highland and lowland deciduous forest, dominated by Quercus nigra L. (Water Oak), Ligustrum sinense Loureiro (Chinese Privet), Smilax rotundifolia L. (Greenbrier), Lonicera maackii (Ruprecht) Herder (Amur Honeysuckle), and L. japonica Thunberg (Japanese Honeysuckle). Quercus alba L. (White Oak) and Fagus grandifolia Ehrhart (American Beech) are more abundant in highland habitat, whereas Betula nigra L. (River Birch) and Liquidambar styraciflua L. (Sweetgum) are populous in lowland habitat (Christopher and Barrett 2006, Klee et al. 2004). Methods Twenty white PVC (polyvinyl chloride) and twenty black ABS (acrylonitrile butadiene styrene) tubes, 7.6 cm in diameter and 30.5 cm in length, were capped on both ends. Holes (2.5 cm in diameter) were drilled into the caps on each end to provide entrance/escape portals. Nonabsorbent cotton was positioned in half the length of each tube to provide bedding material. An experimental grid (approximately 1 ha) was established in each of the highland and lowland habitats. Ten Water Oaks were selected in the lowland grid, and ten White Oaks were selected in the highland grid. Each oak tree (highland mean DBH = 81.4 ± 10.4 [SD] cm and lowland mean DBH = 43.63 ± 8.14 [SD] cm) represented a sample station. Each station was comprised of two platforms mounted 180º from each other 1.5 m aboveground level. Adjacent stations were spaced on average 8.04 ± 2.02 (SD) m apart. On each tree, one 7.6-cm-diameter white tube and one 7.6-cm-diameter black tube was mounted on wooden platforms using bungee cords (Fig. 1). Directions 2011 L.L. Catall, D.L. Odom, J.T. Bangma, T.L. Barrett, and G.W. Barrett 511 of the platforms (360º) were randomized. Nest tubes were checked weekly from 16 February 2009 to 17 March 2010. When checking nest tubes for smallmammal occupancy, a #5 rubber stopper was fitted into each of the two-entrance/ escape portals. Each nest tube was then placed into a 32 gal (121.6 l) Rubbermaid roughneck container to remove cotton and handle captive individual(s). Location, species, ear tag number, sex, reproductive condition (females open or Figure 1. Image of a station encompassing one black and one white tube positioned on platforms attached to a tree 1.5 m aboveground, Horseshoe Bend Ecology Experimental Site. Photograph © Terry L. Barrett. 512 Southeastern Naturalist Vol. 10, No. 3 closed vaginal orifice; males abdominal or scrotal testes), and weight of each captured individual were recorded. Captured individuals were released at the site of capture. From 14 November 2009 to 26 February 2010, dual probed maximum/ minimum thermometers (Digital Dual Sensor Thermometers SN 89212, Forestry Supplies, Inc.) were inserted into each white and black nest tube cavity to measure daily ambient temperatures inside each nest tube. Two random stations, one in the highland and one in the lowland grid, were used to determine mean weekly temperature differences between the black and white tubes. Thermometers were rotated to new stations on a weekly basis. Mean weekly ambient temperatures were also recorded. A chi-square test was performed to determine treatment differences in nest tube selection (black versus white) by White-footed Mice and Golden Mice. We hypothesized that small mammals would select black versus white tubes in equal proportions (50/50). Significant differences were determined at the P ≤ 0.05 level of probability. Results and Discussion Only White-footed Mice and Golden Mice used the nest tubes during this investigation, likely because of the diameter (2.5 cm) of entrance/escape portals. White-footed Mice (n = 103) and Golden Mice (n = 27) used these artificial nest cavities during all seasons except summer; peak use occurred during winter months. Use of nest tubes by adult White-footed Mice during winter months of December through February included 15 females and 13 males in black nest tubes and 1 female and 6 males in white nest tubes. Use by adult Golden Mice during these same months, were 3 females and 1 male in black nest tubes and 7 females and 6 males in white nest tubes. These data confirm that White-footed Mice dominate use of black nest tubes during the winter breeding season. Birthing (n = 13) occurred only in black nest tubes for both small-mammal species. Birth of young began on 17 December for White-footed Mice and not until 27 January for Golden Mice. There was a significantly greater use of black nest tubes by White-footed Mice, compared to white nest tubes, throughout this investigation (χ2 = 33.8, df = 1, P ≤ 0.01). There was no significant difference between black compared to white nest-tube use by Golden Mice (χ2 = 0.04, df = 1, P > 0.25). We are not certain why White-footed Mice and Golden Mice did not use the nest tubes during summer. However, Wolff and Hurlbutt (1982) and Wolff and Durr (1986) found that White-footed Mice nested underground or in hollow trees during summer. Madison et al. (1984) reported that White-footed Mice nested singly in trees during summer. Southern populations of Golden Mice breed mostly during winter, and avoid breeding during summer (Linzey and Packard 1977, McCarley 1958, Pearson 1953, Rose 2008), suggesting less need for use of nest tubes during summer. We observed the same breeding pattern at HSB, which may partially explain why Golden Mice did not use nest tubes during summer. Because black tubes were preferred over white tubes, we explored mean weekly maximum and minimum temperature within each colored tube during 2011 L.L. Catall, D.L. Odom, J.T. Bangma, T.L. Barrett, and G.W. Barrett 513 winter months in both the highland and the lowland forest habitat (i.e., from mid-November 2009 through late February 2010). Mean weekly ambient temperatures were also recorded during this same time period (Fig. 2). Black tubes reached a higher daily maximum temperature than did the white tubes. Mean recorded maximum temperatures in the black tubes were 2.5 ºC greater than in the white tubes throughout the winter months. Black and white tubes reached similar minimum temperatures at night throughout the course of the study (Fig. 2). Our study proposed to create an economical artificial nest cavity that property owners can use to attract small mammals. As noted, the black nest tube cavities were used more frequently than the white ones. An estimated cost to construct a single black ABS nest tube is approximately fifteen U.S. dollars ($15.00) excluding labor (i.e., similar to or less expensive than numerous avian nest-box designs). 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