See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/220028468 Sexual disparity in activity patterns and time budgets of angulate tortoises (Chersina angulata) on Dassen Island, South Africa Article in African Zoology · October 2006 DOI: 10.3377/1562-7020(2006)41[224:SDIAPA]2.0.CO;2 CITATIONS READS 13 77 3 authors: Toby Keswick Brian Henen University of the Western Cape 116 PUBLICATIONS 1,379 CITATIONS 7 PUBLICATIONS 40 CITATIONS SEE PROFILE SEE PROFILE Margaretha Hofmeyr University of the Western Cape 87 PUBLICATIONS 664 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Headstarting Agassiz's Desert Tortoises View project Tortoise ecology and conservation View project All content following this page was uploaded by Toby Keswick on 24 July 2014. The user has requested enhancement of the downloaded file. Sexual disparity in activity patterns and time budgets of angulate tortoises (Chersina angulata) on Dassen Island, South Africa Toby Keswick, Brian T. Henen & Margaretha D. Hofmeyr* Chelonian Biodiversity and Conservation – Southern Africa, Department of Biodiversity and Conservation Biology, University of the Western Cape, Private Bag X17, Bellville, 7535 South Africa Received 13 September 2005. Accepted 11 January 2006 Behavioural frequencies and time budgets for male and female Chersina angulata were recorded in spring, September 2004. The daily activity of the population was 10.51 ± 0.42 h (mean ± CI), but individual males and females were in the open for 2.57 ± 1.12 h and 1.58 ± 1.44 h, respectively. Both sexes spent nearly 3.5 h per day basking with 90% of the basking time in the cover of sparse vegetation. Feeding and walking were the most frequent active behaviours. The activity pattern of the sexes differed between 10:00 and 12:00 in the morning when males spent more time out of cover on active behaviours, particularly feeding, than females did. The daily activity pattern of the population peaked between 10:00 and 12:00, reflecting the activity pattern of the more active sex, males. Females were out of cover, active, and feeding at higher temperatures than were males. The high temperatures probably allowed females to complete activities more efficiently, reducing their exposure time and predation risk. Although fighting and mating represented small fractions of male time budgets, the extended physical presence through walking and feeding may help males to establish dominance hierarchies and enhance mating success. Key words: activity pattern, behaviour, temperature, thread-trailing, time budget, tortoise. INTRODUCTION duce at any particular point in time (Wolf & Field studies of animal behaviour have progressed Hainsworth 1971). Time budgets may also differ from being largely descriptive to quantifying and between sexes due to sexual differences in repro- explaining observed behaviour. This change is not ductive behaviours (e.g. male displays, male–male to be perceived as one superseding the other, as combat, and mate choice by females). without description there can be no explanation A number of studies have evaluated activity and (Altmann & Altmann 2003). By observing and behaviour patterns in chelonians (Rose & Judd describing functional traits (e.g. foraging), we can 1975; Douglass & Layne 1978; McRae et al. 1981; investigate causality (e.g. foraging to provide Brown & Brooks 1993; Kazmaier et al. 2001). Few energy for sexual reproduction) and form falsi- studies, however, constructed time budgets fiable hypotheses (Altmann & Altmann 2003). (Hailey & Coulson 1999) and evaluated the differ- Testing such hypotheses may provide insight into ent time allocations of the two sexes (Lagarde et al. the importance of behaviour to the perpetuation 2002). Researchers often use undirected searches, of a species and thus assist in conservation opportunistic encounters, or continuous short- (Altmann & Altmann 2003). term observations of individuals to evaluate Time budgets document the time spent in activity patterns and the frequencies of different behavioural categories (e.g. walking) and have behaviours for the population. Time budgets been compiled for several taxa, including birds based on results from these sampling methods, (Wolf & Hainsworth 1971; Bubier 1996) and however, can grossly overestimate the activity mammals (Weller & Bennett 2000; Sharpe & Rosell level of individuals (Moskovits & Kiester 1987; 2002). Time budgets are valuable as they describe Hailey & Coulson 1999). Accurate estimates of behavioural allocation for individuals or groups the frequencies and durations of the different in relation to their environment – one obvious behaviours require continuous monitoring of example being behavioural changes among individuals throughout the daily activity period of seasons. An individual’s behaviour may be a the population (Hailey & Coulson 1999). Thread- reflection of what it needs to survive and repro- trailing (Breder 1927) facilitates observation of *Author for correspondence. E-mail: [email protected] specific individuals and Hailey & Coulson (1999) African Zoology 41(2): 00–00 (October 2006) 2 African Zoology Vol. 41, No. 2, October 2006 used thread-trailing to compile time budgets for South Africa (33°25’S, 18°5’E). The vegetation the Speke’s hinged tortoise, Kinixys spekii. consists of large open areas with low-growing Temperature is an important aspect to consider mosses and annuals interspersed with taller plants when constructing time budgets of ectotherms. (c. 25–100 cm). The open vegetation and the Most reptiles have a preferred body temperature extremely high density of angulate tortoises range and may use different behaviours to achieve (c. 100–200 tortoises per hectare; M.D. Hofmeyr, and maintain eccritic temperatures (Pough et al. unpubl. data) made it possible to monitor popula- 2001). Temperature influences the metabolic rate tion activity while doing focal observations on of reptiles and active behaviours may require individuals. higher body temperatures than passive behaviours (Meek 1988). The low metabolic rate of ectotherms Data collection and the effect of temperature on their activity may In order to compare male and female activities explain why many chelonians remain inactive for under the same weather conditions, we observed long periods of the day (Douglass & Layne 1978; one male and one female simultaneously per Pough 1980; Nagy & Medica 1986; Lagarde et al. day. We used thread-trailing to facilitate the track- 2002). ing and simultaneous observation of the two There has been only one explicit study of the individuals; thread-trailing also helped minimize behavioural activity of Chersina angulata. Ramsay or eliminate observer disturbance of tortoise et al. (2002) found that weather conditions influence behaviour. We obtained complete data sets (from the daily and seasonal activity patterns of angulate sunrise to sunset) for 10 male–female pairs between tortoises and that tortoises are more active in 10 and 30 September 2004 (early spring). On the spring than at other times of the year. Structured eve of each study day, we chose one adult male searches revealed that a larger proportion of male and one adult female, in close proximity to one than female tortoises is active in spring and in another, for our focal observations the next day. summer. Chersina angulata males engage in Tortoises were found partially buried in vegeta- agonistic behaviours in spring (Ramsay et al. 2002; tion and we selected two tortoises with similar Mann et al., in press), a time when females are amounts of cover to not bias emergence times the vitellogenic and still nesting (Hofmeyr 2004). following day. Ramsay and co-workers engaged several methods We used duct tape to fit a simple harness to collect behavioural data from angulate tortoises. containing 150 m of cotton thread to the carapace These methods were suited to population sam- of the tortoise. The loose end of the thread was tied pling and the authors did not monitor the behav- to a flag planted near each tortoise to help locate iour of individual tortoises throughout the day. tortoises at the beginning of the observation day. In this study, we used focal observations of Applying the harness required only a few minutes individual males and females to characterize the of gentle handling and after the harness was behaviour of angulate tortoises in spring. The attached, most tortoises remained at the same results of individuals were interpreted against position; some tortoises moved a few metres to a results from population scans obtained under new refuge. Because the disturbance was minimal similar weather conditions. Our objectives were and the tortoises had more than 12 hours to recover, to: 1) determine if male and female angulate we assumed that tortoise activity the next day was tortoises spend the same amount of time on spe- not affected by the procedure. cific behaviours; 2) establish if the temporal Observation days began at 07:00 and ended at pattern of behaviour is similar for the sexes; 18:30, approximately sunrise and sunset, encom- 3) evaluate if males and females perform specific passing the activity period of C. angulata in behaviours at similar temperatures; 4) construct September 2004. The observer was positioned detailed time budgets for both sexes, and 5) evalu- between the two focal animals, and used the ate the information provided by focal and popula- instantaneous sampling method (Altmann 1974) tion scan methods.