Volume 78 Part 4

JournalJournal of ofthe the Royal Royal Society Society of ofWestern Western Australia, Australia, 78(4), 78:107-114, December 1995 1995 Foraging patterns and behaviours, body postures and movement speed for goannas, Varanus gouldii (Reptilia: Varanidae), in a semi-urban environment G G Thompson Edith Cowan University, Joondalup Drive, Joondalup, WA 6027 Manuscript received July 1995; accepted February 1996 Abstract Two Gould’s goannas (Varanus gouldii) were intensively observed in the semi-urban environment of Karrakatta Cemetery, Perth, Western Australia. After emerging and basking to increase their body temperature, they spent most of their time out of their burrows foraging, primarily in leaves between grave covers, and under trees and shrubs. Mean speed of movement between specific foraging sites was 27.6 m min-1, whereas the overall mean speed while active was only 2.6 m min-1 because of their slower speeds while foraging. A number of specific body postures were observed, including; vigilance, walking, erect, and tail swipes. Specific feeding and avoidance behaviours were also recorded, along with the influence that two species of birds had on their selection of foraging sites. Introduction Methods Our knowledge of foraging habits, patterns, home Study Site range and activity area size, posture, and behaviour for Karrakatta Cemetery (115° 47' E, 31° 55' S) is located large goannas has been extended since the early work of within the Perth metropolitan area, approximately 4 km Cowles (1930) with V. niloticus, and Green & King (1978) west-south-west of the city centre. It has 53 ha allotted with V. rosenbergi. Recent comprehensive studies include to burial plots and another 53 ha to roads, ornamental those by Auffenberg (1981a,b; 1988; 1994) for V. gardens and buildings. The cemetery is planted with a komodoensis, V. bengalensis and V. olivaceus, Auffenberg range of exotic shrubs and trees, with many of the north- et al. (1991) for V. bengalensis, Daltry (1991) for V. ern, central and eastern areas being grassed. There are salvator, and Weavers (1993) for V. varius. General de- numerous rose gardens to the south and east of the main scriptions of varanid locomotion, postures and foraging entrance, which are located on the northern boundary behaviour are given by King & Green (1993 a,b). How- (see Thompson 1992, 1994). A nature reserve of ap- ever, there remains a paucity of data concerning the proximately 7 ha is located on the south-eastern bound- behaviours, body postures and movement patterns of ary. The study site was located in the southern section small and medium sized varanid lizards. of the cemetery (Fig 1). Pianka (1994) reports that Australian desert goannas, such as V. gouldii, are exceedingly wary, unapproachable, Monitoring procedures and unobservable; this consequently makes it very diffi- A miniature radio-transmitter with a battery life of cult to study their use of time and space, foraging approximately 140 days (11 g mass; TX1 1C tempera- behaviour and body postures. Because V. gouldii at ture-pulse, Bio-Telemetry Tracking) was attached to the Karrakatta Cemetery have learned to accommodate to lateral aspect of the base of the tail for seven V. gouldii in the presence of people, this site provides a unique op- early November, 1993. The radio transmitter was sewn portunity for a study of their behaviour and foraging into a denim harness that was glued with Selleys ‘kwik- patterns that is not possible in more remote locations. grip’ to the skin of the goanna’s tail to encircle the tail This study is the third in a series (Thompson 1992, for a length of approximately 50 mm. Each goanna was 1994) on the movements, behaviours and ecology of V. located prior to observations commencing each day with gouldii at Karrakatta Cemetery, Perth, Western Austra- a Bio-tel RX3 receiver operating in the 150-151 MHz lia. The earlier papers report on the daily distance trav- band in conjunction with a 3EY directional antenna. The elled, foraging areas and the size of the activity area behaviour and daily movements of five of these V. during the breeding season. The primary objective of gouldii were initially monitored to choose two goannas this study was to examine in detail the behaviours, pos- that readily adapted to being observed. Behavioural ob- tures and preferred micro-habitat foraging sites for two servations over five weeks commenced on these two V. particular individual V. gouldii. gouldii [#1, a female, with a body mass of 330 g, snout- to-vent length (SVL) of 314 mm; and #2, a female, with a body mass of 348 g and SVL of 300 mm] on 1 December 1993 and concluded on 18 January 1994. This study was © Royal Society of Western Australia 1995 conducted in conjunction with a study that continuously 107 Journal of the Royal Society of Western Australia, 78(4), December 1995 Figure 1. Karrakatta Cemetery, showing the study site vegetation and V. gouldii activity areas. monitoring of the body temperature of these V. gouldii Foraging, movement and posture recording procedures over a number of months using temperature sensitive Observations for each goanna on the choice of forag- transmitters attached to the lizards and a data-logger ing site, general habitat, extent of exposure to the sun connected to a large stationary antenna. and distance moved were recorded for the previous nine minute interval in the categories shown in Table 1. During the first week of observation, each goanna Movement behaviour for each nine minute period was was initially monitored from a distance of approxi- classified into seven categories (Table 1). Data reported mately 50 m. After this adjustment period, most obser- for the micro-habitat of foraging sites, general habitat vations were then carried out from a distance of 15 to 35 type selected, extent of exposure to the sun, and dis- m. On numerous occasions, the observed V. gouldii tance travelled, include only the time between when the moved toward the observer, reducing the distance to goanna commenced foraging to when it either returned observer to less than 5 m, and on a few occasions to less to a burrow or observations ceased (but excludes the than 2 m. This suggests that the presence of an observer time between when the goannas emerged from their had a minimal influence on their behaviour. The data overnight burrow and when they were first observed from the first week of observation of the two V. gouldii basking in the sun to increase their body temperature were not analysed, as this period allowed these two V. Tb). Goannas often moved through various sites during gouldii to adjust to the continued presence of an ob- the nine minute period. The predominant environment server. for the period is the one reported. The number of times Two well trained observers spent a total of 131 hours that V. gouldii #1 was seen to capture a prey item was watching and recording data for these two V. gouldii or also recorded, and is reported as the mean number of waiting for them to emerge from their burrows, but they minutes between successful strikes. In addition, observ- never spent more than half a day observing one goanna, ers recorded the time when the goanna produced a scat, to minimise any impact that these observations might its behaviour and when the two V. gouldii were harassed have had on their normal behaviour. The recording pro- by birds. Observers also noted the feeding and digging cedures of the two observers were checked every couple behaviours for these two goannas. of days during the first two weeks to ensure consistency In late December, 1993, both goannas were recorded of observations and recording of data. by video camera for a total of 6 hours, (four hours for 108 Journal of the Royal Society of Western Australia, 78(4), December 1995 Table 1. Alternatives used to classify the foraging sites, general habitat, extent of exposure to the sun and movement behavior. Micro-habitat foraging sites General habitat type selected Extent of exposure to the sun Movement behaviour Between grave covers Between graves Total sun Emerging from an overnight burrow Leaves under trees or shrubs On top or the side of graves ¾ sun Basking but not moving Under grave covers Under grave covers ½ sun Basking and moving Leaves in an open area Grassed areas ¼ sun Moving about outside a grave cover Grass in an open area On the road verge All of the time in the shade Moving under a grave cover Grass under trees or shrubs Treed areas Under grave cover or in a burrow Stationary and looking In the yards of adjacent houses Avoidance (people, dogs, birds, vehicles) Up a tree In the nature reserve (heavily grassed with ' 50% tree canopy) one and two hours for the other), over a four day period or between foraging sites, their actual movement path and body postures were drawn from these video im- was generally a series of near linear movements. These ages. Reference to this visual record was also used to were summed for each period. For example, if a goanna clarify the written descriptions of each observer for pos- was to circumambulate a grave cover the total linear tural, feeding and digging behaviours. distance would be approximately 10.8 m presuming it The linear distance that each of the two V. gouldii moved midway between adjacent grave covers. From moved during each nine minute observation period was these data, the mean distance travelled per minute was estimated by recording the number of grave lengths and calculated. The average speed of movement between widths (3.6 m and 1.8 m respectively) that the goanna foraging sites was estimated by recording the time, to had passed during the period.

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