Daily activities of immature Komodo monitors Varanus komodoensis


Daily activities of immature Komodo monitors Varanus komodoensis

M Jeri Imansyah

mjimansyah@yahoo.co.id

Method

To assess patterns in daily activities Radiotelemetry was used to observe hatchlings and the juveniles. This study was conducted between March and June over 2 years (2004-2005). Telemetry equipment consisted of activity-sensitive AVM G31V transmitters (AVM Instruments Co. Ltd.), an AVM LA12Q receiver, and a three-element Yagi antenna. Transmitters were attached to the monitor’s tail base using duct tape (Imansyah et al., 2007). After the transmitters were attached, hatchlings and juveniles were released immediately. Each animal was radio-tracked for 7 – 56 days (mean 31.42 ± 5.05 days). Initial observations showed that radio-tracked Komodo monitors never moved during the night. To increase independency of the data, individual daily observations were conducted in four sessions; separated by a minimum daily time interval of 2-3 hours. Daily positions and habitat use observations were made from 6am to 6pm across 4 time periods of morning (0600-0900h), late morning (0900-1200h), afternoon (1200-1500h) and, late afternoon (1500-1800h).

Results

Several differences were detected in daily activity patterns between hatchling and juvenile Komodo monitors. A significant difference was detected in daily activity patterns between hatchlings and juveniles. Both hatchling and juvenile Komodo monitors were tend to be less active (Chi Square χ2 = 21.26 p ≤ 0.001; T-test; t1,287 = -15.32, p ≤ 0.001 for hatchling and T-test; t1,305 = -12.35, p ≤ 0.001 for juvenile; Figure 1a), however, juveniles were more active than hatchlings (Chi Square χ2 = 28.51 p ≤ 0.001; Figure 1a).

There was a dial activity pattern displayed with two peaks of activity, first between 0900 and 1200 and the second between 1500 and 800. Hatchlings were more active in the afternoon (1500 – 1800) than juveniles were (0900 – 1200). However, juveniles also displayed their ability to be active at anytime during the day 0600 – 1800 after basking in the morning. Activity patterns were significantly differ among activity times in both hatchlings and juveniles (ANOVA F3,276 = 33.97, p ≤ 0.001 for hatchling and ANOVA F3,302 = 60.47, p ≤ 0.001 for juvenile, Figure 1b). The study reported that hatchlings mostly conducting travel between 0900 – 1200 and secondly between 15-18h but did not travel before 9h (Figure 1c). In contrary, juveniles were able to conduct traveling activity at any time even thought they were mostly conducted traveling between 9-12h (Figure 1c).

Mean daily air temperatures in Loh Liang was different among time of activities (ANOVA F3,2924 = 1624.56, p ≤ 0.001, Table 2). There was a significant correlation between daily activities and daily air temperatures (Pearson correlation test; r = 0.36, p = 0.04).

DISCUSSION

In general, both hatchlings and juveniles were less active during the study, they spent most of their diurnal periods for resting rather than for traveling or foraging and no activity were recorded during nocturnal periods. This activity pattern was similar to those reported in adult Komodo monitors by Sastrawan & Ciofi (2002). However, inactivity periods among hatchlings, juveniles and adult Komodo monitors were often followed by intense movement periods afterward (Imansyah et al., 2008; Sastrawan & Ciofi, 2002). Similar inactivity pattern was also reported in other Varanid like V gouldii and V panoptes (Christian et al., 1995) and other reptile species such as Broad-headed snake Hoplocephalus bungaroides (Webb & Shine, 2001), Brown snake Pseunaja textilis (Whitaker & Shine, 2003).

A nonuniform pattern on activity distribution was reported from this study, however, both hatchlings and juveniles displayed bimodal peak of activity time in the late morning (0900 – 1200) and late afternoon (1500- 1800). Adult Komodo monitors were also reported to have bimodal activity time in the morning (0800 – 1000) and in the late afternoon (1600 – 1800) (Sastrawan & Ciofi, 2002). Unlike hatchlings, juveniles were displayed to have ability to be active at anytime during their diurnal activity period like those reported in adults (Sastrawan & Ciofi, 2002). However, Auffenberg (1981) reported that during rainy seasons, particularly between January and March, Komodo monitors activity were more concentrated to the warmest hours. Similar to Komodo monitors, Ibrahim (2002) reported that V. griseus daily peak of activity was in the late morning (0900-1000h) and ability to be active at anytime during the day. Another monitor, V. caudolineatus, was active during late morning and early afternoon and positively correlated with the highest temperature at that time (Thompson, 1993). In contrast, Amat et al. (2003) reported that immature Lacerta agilis lizard were displayed a unimodal activity pattern that occur in the morning. As reported by (Heatwole 1976), among immature life stages it is common to have different activity cycles.

Most of hatchlings activity is carried out on tree as they displayed arboreal characteristic during this age (Imansyah et al., 2008). Arboreal character in hatchlings was believed as a mechanism to avoid predator, cannibalism, and competition among conspecific, therefore this life stage performed the least active compared to other age class (Auufenberg, 1981; Sastrawan & Ciofi, 2002). Early post natal movement in lizard is often resulting in fidelity and important to to assess resource acquisition and success in reproduction (Rose, 1981; Sumner, 2006). Further, activity and movement in immature lizards are often associated with avoidance of predatory and resource competition with adults (Auffenberg, 1981; King & Green, 1999). Webb and Shine (1997) reported that specific thermal regimes driven species to select specific retreat sites.

This study also reported influence of environment temperatures to immature Komodo monitor’s daily activities. During the study, both hatchlings and juveniles were more active in the late morning and afternoon when the average temperatures were 29.58 and 29.57 °C consecutively. Climatic and physical characteristic of environment, play a great role in influencing activity patterns in reptiles which is tend to display their favorable in particular preferred range conditions (Rose, 1981). Pianka (1986) described that reptiles are highly dependence on particular suitable temperature condition and appropriate body temperature for their activity. Although not depend on particular temperature to initiate their activity, animals have discrete times of the day in which activity is concentrated and are relate to environmental factor, i.e. temperature (Heatwole, 1976). Most lizards are changing their activity patterns in synchrony with changes in environments (Porter et al. 1973). In Whiptail lizard Aspidoscelis inornata and A. gularis initiation of daily activity has been hypothesized to be dependent upon the achievement of some critical soil temperature for lizard emergence, while cessation of activity is hypothesized to be the direct result of increasing afternoon soil temperatures that may be thermally stressful (Winne & Keck, 2004). Activity in lizards was also influenced by the intensity of solar radiation that could be a limiting factor (Christian & Weavers, 1984).

~ oleh ekologi pada Juni, 18, 2008.

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