Nest box use by woodland dormice (Graphiurus murinus) - Springer Link

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Mar 18, 2010 - Nest box use by woodland dormice (Graphiurus murinus): the influence of life cycle and nest box placement. Zimkitha J. K. Madikiza & Sandro ...
Eur J Wildl Res (2010) 56:735–743 DOI 10.1007/s10344-010-0369-x

ORIGINAL PAPER

Nest box use by woodland dormice (Graphiurus murinus): the influence of life cycle and nest box placement Zimkitha J. K. Madikiza & Sandro Bertolino & Roderick M. Baxter & Emmanuel Do Linh San

Received: 25 November 2009 / Revised: 15 February 2010 / Accepted: 18 February 2010 / Published online: 18 March 2010 # Springer-Verlag 2010

Abstract The use of nest boxes by the woodland dormouse, Graphiurus murinus, was investigated over a 13-month period in a riverine forest of the Great Fish River Reserve, South Africa. We predicted that some characteristics of nest box placement would affect nest box use and that the seasonal pattern of nest box use would be linked to the species' life cycle and physiological and socioecological characteristics. Generalized linear models indicated that the time since nest box installation and nest box height above ground positively affected the frequency and intensity of nest box use. Male and female dormice, as well as adults and juveniles, did not differ in the number of nest boxes used and equally occupied individual nest boxes. The percentage of nest boxes used peaked during spring and summer (breeding period) and dropped during winter (hibernation). However, whereas significantly more males were caught during the mating season (spring), the number of females occupying nest boxes was constant during the year. As female dormice successfully

Communicated by: C. Gortázar Z. J. K. Madikiza (*) : R. M. Baxter : E. Do Linh San Department of Zoology and Entomology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa e-mail: [email protected] S. Bertolino DIVAPRA, Entomology & Zoology, Via L. da Vinci 44, 10095 Grugliasco, Turin, Italy Present Address: R. M. Baxter Department of Ecology and Resource Management, School of Environmental Sciences, University of Venda, Private Bag X5050, Thohoyandou 0950, South Africa

bred in the nest boxes, the observed sexual patterns suggest that (artificial) nest sites represent an important resource for females, whereas females seem to constitute the main resource for males, as predicted by the socioecological model. Keywords Gliridae . Artificial nest sites . Nest box use . Capture–mark–recapture . Breeding period . Hibernation

Introduction Artificial nest sites, most commonly in the form of nest boxes that are attached to a tree, are readily used by several hollow-using animals belonging to various systematic groups, including birds (e.g., Petty et al. 1994; Mand et al. 2005), arboreal marsupials (Menkhorst 1984; Lindenmayer et al. 2003), bats (Kowalski and Lesinski 1994; Ciechanowski 2005), arboreal rodents (Barkalow and Soots 1965; Morris et al. 1990; Shuttleworth 1999; Juškaitis 1999; Marsh and Morris 2000), and invertebrates (e.g., wasps, ants, beetles, etc.). As a consequence, nest boxes may constitute important survey and research tools (Myers and Dashper 1999; Harley 2004). In population biology studies, the use of artificial nest sites by arboreal species for breeding purposes is of prime importance, since data on breeding period, litter size, or growth rate can be collected by monitoring the boxes on a regular basis. Furthermore, irrespective of the proportion of individuals from an animal population using nest boxes, seasonal, sexual and age-related variations in nest box use might shed light on the species' ecology, physiology, and sociospatial organization. Dormice (Family Gliridae) constitute a group of largely arboreal rodents distributed in the Palaearctic and Ethiopian faunal regions (Holden 2005). Due to their small size (adult body weight ranges from 15 to 200 g) and nocturnal and

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hole-nesting habits, dormice are notoriously difficult to study in their natural habitat without the help of live traps, radio transmitters, and nest boxes. The latter have been used by zoologists to collect information on aspects as diverse as geographical distribution (e.g., Andera 1994; Juškaitis 1994), population structure and dynamics (e.g., Burgess et al. 2003; Juškaitis 2003; Kryštufek et al. 2003), reproductive cycle and breeding patterns (e.g., Juškaitis 1997a; Buechner et al. 2003), spatial behavior (Juškaitis 1997b; Buechner 2008), or physiology (Juškaitis 2005). Wooden nest boxes are also used extensively in countrywide monitoring programs (Bright et al. 2006). Whereas a substantial knowledge has been acquired on European dormice species, comparatively little is known about the biology and ecology of African dormice. According to Holden (2005), there are currently 15 dormouse species on the African continent, 14 of which belong to the genus Graphiurus. One of them, the woodland dormouse, G. murinus, possesses a very broad geographical range that stretches from Ethiopia in the North to South Africa in the South and from Angola in the West to Mozambique in the East (Skinner and Chimimba 2005). However, current knowledge on G. murinus is largely limited to dietary habits (e.g., Baxter et al. 2005) and physiological aspects. The species is described as a competent thermoregulator, with dormice maintaining a body temperature of between 34°C and 38°C either by increasing activity and making postural adjustments at low ambient temperatures or salivating at high ambient temperatures (Whittington-Jones and Brown 1999). Under laboratory conditions, Webb and Skinner (1996) noted that summer-acclimatized dormice used daily torpor spontaneously as an energy-saving mechanism in response to food deprivation. Ellison and Skinner (1991) further described that coldacclimatized dormice entered hibernation (i.e., prolonged bouts of torpor were observed), characterized by a decrease in body temperature and a decrease in body weight. Mzilikazi and Baxter (2009) showed that, in the Great Fish River Reserve (South Africa), free-ranging woodland dormice similarly undergo multiple-day torpor bouts of up to 96 h during winter, with body temperature reaching a minimum of 2.5°C. The use of heterothermy in dormice implanted with data loggers was observed for up to 98% of all measurement days (Mzilikazi and Baxter 2009). In this paper, we present for the first time data on the nest box utilization by the woodland dormouse. Considering that, throughout its distributional range, this species is associated with woodlands (Smithers and Wilson 1979) and that it uses tree holes as nest sites (Kingdon 1974; Skinner and Chimimba 2005), we predicted that (1) woodland dormice would use nest boxes for resting and nesting, allowing the use of this technique for population studies. A woodland habitat is a patch with a set of environmental conditions and resources that favor occupancy, survival, and

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reproduction by individuals of a given species (Morrison et al. 1992). We thus also predicted that (2) site characteristics within the study area where nest boxes were placed (e.g., tree species, trunk dimension, position on the tree) would influence their occupation by dormice. Studies on other dormice species highlighted a differential use of nest boxes by animals, according to season, life cycle, and individual characteristics (Burgess et al. 2003; Kryštufek et al. 2003; Buechner et al. 2003; Juškaitis 2008). However, as mentioned above, the woodland dormouse is a poorly studied species and information on its life history traits, mating system, and social organization are very scanty. Thus, our hypothesis was that woodland dormice (3) would use nest boxes with seasonal differences related to the physiological (i.e., torpor, hibernation) and reproductive cycle and that (4) sexual and/or age-related differences could provide some information on the socioecology of that species.

Materials and methods Study area The study was carried out in the Great Fish River Reserve (GFRR; 33°11′ S, 26°38′ E) which is situated about 30 km north of Grahamstown, in the Eastern Cape Province, South Africa. The conservation area was designated in 1973 and enlarged in 1983 and 1987, respectively (Birch 2000), and the total combined size is approximately 445 km2. The reserve complex was created from cattle farms with heavily transformed natural vegetation. It is currently made up of three entities (Fig. 1). Our study site was located in the western part, namely, the Andries Vosloo Kudu Nature Reserve. The region has a characteristic undulating terrain, with the elevation ranging from 170 m at the river up to 800 m on the ridges (Palmer and Tanser 1999). The area is relatively arid (summer temperatures are often >40°C), with an annual rainfall of between 400 and 500 mm, which peaks in October–November and February–March. The dense thickets and clumps of thorny and succulent shrubs are major features of the reserve. The area falls within the Albany Thicket Biome with the “Great Fish Thicket” being the dominant vegetation type throughout the GFRR complex (Hoare et al. 2006). Our study was conducted in a stretch of “Riverine Combretum Thicket” dominated by stands of Cape bush willows, Combretum caffrum. This species is prone to rotting from the inside, resulting in numerous holes and hollows, and this in virtually every Combretum tree present. The riverine forest supports several other tree species: Acacia karoo, Acalypha glabrata, Olea europaea ssp. africana, Ziziphus mucronata, and Schotia afra. Beneath these trees, Azima tetracantha, Scutia myrtina, Ehretia regida, Carrisa bispinosa ssp.

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Fig. 1 Location of the Great Fish River Reserve complex. AVKNR Andries Vosloo Kudu Nature Reserve, SKNR Sam Knott Nature Reserve, DDGR Double Drift Game Reserve. The sampling site of “Junction 9” is indicated by a gray-shaded star

GREAT FISH RIVER RESERVE COMPLEX (445 km2) (Eastern Cape Province, South Africa) AFRICA

DDGR

South Africa

(150 km2)

Farming area

N

Junction 9 site

0

(230 km2)

SKNR

5

AVKNR

SKNR

(65 km2)

10

km

bispinosa, and Maytenus heterophylla often form dense undergrowth. On both sides, the study area is bordered by relatively large expanses of “Bushclump Karroid Thicket”, a semi-open habitat composed of Rhus species and S. myrtina bush clumps and a karroid herbaceous layer. Nest box design and monitoring Seventy wooden nest boxes with entrance hole diameter of 3 cm and removable lid were erected at the study site (altitude, 300 m), called “Junction 9.” Nest boxes were made of wood, approximately 2 cm thick, with internal dimensions of 11.5× 13×12 cm (breadth×length×height). Nails were fixed on trees and nest boxes were hanged on nails by a wire sling, with the entrance hole facing the tree trunk, so as to be more accessible to small mammals climbing the tree or branch. This design was also intended to deter birds from entering by obstructing their direct line of flight to the entrance hole (Morris et al. 1990). Two transverse spacing bars, above and below the entrance hole, held the box about 2.5 cm clear of the tree to which it was attached, allowing dormice to squeeze in. Nest boxes were located in a 2.5-ha (breadth×length, 100×250 m) area inside the study site. No attempt was made to install the boxes in subjectively assessed “good” sites. Rather, they were set arbitrarily and spaced irregularly along a curvilinear path across the forest. The 70 nest boxes were erected in five stages (the number of nest boxes is given in parentheses): March 2003 (10), January 2004 (10), March 2005 (20), May 2005 (22), and January 2006 (8). Nest boxes were placed at variable heights, from 1.10 to 2.35 m above the ground (average 1.65±0.26 m), in trees with trunk diameter at nest box height of 90±38 cm (range, 20– 211 cm). The number of Combretum trees in a circular plot of 5-m radius around each nest box was 4.1±2.7 (0–10). Nest box utilization by woodland dormice was evaluated by conducting 57 nest box monitoring sessions between

June 2006 and June 2007. On average, 4.4±1.0 inspections (range, 3–6) were conducted each month. During each monitoring session, nest boxes were considered used by dormice if animals were found inside. When dormice were absent, their nests were recognized by a distinctive woven lichen (Usnea barbata) material and the presence of feathers, snake skin, or even dormouse fur. Dormice were rarely found in nests lacking these materials. Nests built by the Mozambique thicket rat, Grammomys cometes, were distinguished by their composition of long woven grass (Hubbard 1972). Some nest boxes were strictly used as food stations by dormice, with insects and/or fruit remains. Manipulation and marking of dormice At the first capture, dormice were transferred into a preweighed Ziploc plastic bag. Dormice were weighed to the nearest gram with a 60- or 100-g spring balance (Pesola, Baar, Switzerland) and lightly anesthetized using diethyl ether. Dormice were then aged and sexed. Age (adult vs juvenile) was determined based on body size, weight, and fur characteristics. Females were differentiated from males based on the appearance of the genitalia and the presence or absence of swollen nipples. Dormice were individually tattooed on one or two ears with a unique number using single-digit spiked tattoo numbers (Hauptner Herberholz, Solingen, Germany) attached to forceps. Once the ear was pierced, tattoo ink was rubbed into the perforations. Any unusual characteristics (marks in the fur, torn or cut ears, short tail) were recorded to further assist with identification in the event of the tattoo being unclear. Data analysis The following seasons were defined: spring (September– November), summer (December–February), autumn (March– May), and winter (June–August). As the variances of

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subsamples were similar (Levene's test, p>0.05) and the data distributions did not generally depart from normality (Kolmogorov–Smirnov test, p>0.05), seasonal, sexual and age-related variations in nest box utilization parameters were evaluated with one-way analysis of variance (ANOVA), post hoc Bonferroni tests, and independent-samples T tests. In some instances, when data were normally distributed but the variance of subsamples was different, a T test for unequal variances was performed. Nonparametric procedures (Kruskal–Wallis and Mann–Whitney U tests) run as a double check delivered similar results. As nest boxes were erected randomly and in successive stages, placement sites presented variable conditions for dormice. Therefore, we generated generalized linear models (GzLMs) to test if three response variables indicative of nest box use were significantly affected by a set of five predictor variables (Table 1). This procedure expands the general linear model so that the dependent variable (binary, count, or continuous) is linearly related to a combination of discrete factors and continuous covariates via a specified link function. Moreover, the model allows for the dependent variable to have a non-normal distribution, as this is generally the case with binary and count data (Norušis 2008). A binomial distribution and a logit link function was chosen for the binary dependent variable (USE), whereas negative binomial distributions and log link functions were used to model the count response variables (ABSFREQ, NODORM). The dispersion parameter k for the negative binomial distributions was set at 0.7 (ABSFREQ) and 1 (NODORM), respectively. The ratio of the deviance to its degree of freedom was close to 1 for all response variables, indicating that the variability in observed data was similar to the one predicted by the underlying distributions used for the models. As independent variables are treated as fixed known values in the procedure, there was no concern as to their distribution.

Data were tabulated in Excel (Microsoft Inc.) and statistical analyses were performed with SPSS, release 15.0 (SPSS Inc.). Unless stated otherwise, figures are reported as the mean ± standard deviation.

Results Dormouse abundance From June 2006 to June 2007, we made a total of 384 captures of 66 different dormice: 11 adult males, 17 adult females, two unsexed adults, and 36 juveniles. On average, 7.60±6.52 (range, 0–29) dormice were found on each checking day (n=57), with significant seasonal variations (F=6.95, df=3, p