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Overnight movement
Study animals moved mostly at night. During daytime radio-tracking study animals were almost always buried or at the seasonal dams. Only 19 (2%) of 976 location fixes obtained for all RT animals represented instances where males were found aboveground during daytime away from water (resting under vegetation). The only daytime overland movements observed were on 6 December 2004 and 6 November 2005 when respectively, 53 mm and 56 mm of rain fell in under an hour during the afternoon, prompting P. adspersus to emerge from their burrows and move rapidly to the seasonal dams.
Animals spent a day or two at spawning events, and four RT males were found guarding offspring on one or two days each in summer. Females, as well as those males that did not remain at the seasonal dams to guard offspring, returned directly to their burrows (Fig. 1, 2). ST males and females exhibited little difference in the distances calculated between their actual post-mating movement away from the seasonal dams and the measured straight line distances between the end points (males: 21.5 ± 24.9%, range = 0.9-65.7%, n = 6; females: 18.4 ± 11.8%, range = 4.7-42.7%, n = 9; Mann Whitney U = 23.00, df = 4, P = 0.64). The maximum known distance moved overnight post-spawning was similar for males (350.5 m) and females (350.4 m).
Spool-tracking revealed that animals readily: used human-created foot paths when returning to their burrows; travelled along the gravel road on the eastern boundary of the site, particularly in furrows on the road side where rain water was channeled; and moved through an electrified fence if it was necessary to reach their burrow (Fig. 1, 2). Since spools were found to only last a night or two, and because nocturnal radio-tracking was not done, limited data on overnight foraging of adult male and female P. adspersus were obtained. We directly observed adult P. adspersus foraging in the evening at the water’s edge and within 20 m of the seasonal dams after several spawning events. An ST male was observed foraging under house lights within 10 m of his burrow (Fig. 1), and a concentration of short, criss-crossing tracks left by another ST male indirectly indicate that this frog foraged within 12 m of his burrow before retiring underground (Fig. 1). The recorded movement of an ST female around a termite mound is perhaps indicative of foraging (Fig. 2).
Seasonal movement
A burrow used by an animal for less than two weeks in a summer was classified as “temporary.” Burrows used for longer periods were classified as “long-term” burrows (LTBs). Temporary burrows were used briefly, for example, by females en route to LTBs (Fig. 3). Empty burrows of either type had an elliptical entrance, and a volume just large enough to contain the inflated body of an adult male or female P. adspersus ca. 150 mm beneath the ground surface. Burrows retained their form, and animals exhibited high burrow fidelity. The number of LTBs used per summer by males (1.1 ± 0.2 burrows, range = 1.0-1.5 burrows, n = 9) and females (1.1 ± 0.3 burrows, range = 1.0-2.0 burrows, n = 9) did not differ significantly (U = 33.00, df = 7, P = 0.51). An electrified fence and vehicle traffic on the tarred road on the western boundary of the site also did not deter two RT males from repeatedly returning to their burrows (Fig. 4). LTBs of animals were measured from the center (not the edge) of the nearest seasonal dam (CNSD) because each dam’s surface area was small (and changed continually in response to weather) relative to large, natural breeding sites (e.g., Glen Austin [~ 9 ha] and Bullfrog [~ 81 ha] pans). LTBs of females were situated almost four times further from the seasonal dams (446.8 ± 295.4 m, range = 119.1-902.7 m, n = 9) than those of males (131.0 ± 105.2 m, range = 33.3-329.8 m, n = 9, U = 11.00, df = 7, P = 0.009). The latter result remained significant following a Bonferroni correction.
Movement among years
Spatial use of habitat by four RT males during two or three successive summers suggests animals had a strong preference and good memory for specific areas (Fig. 5). The proportion of unique relocation points contained within the minimum convex polygons constructed around each summer’s relocation points was 83.1 ± 14.0% (range of 68.8- 100.0%) for all four males across all summers. These animals used between one and two (1.3 ± 0.2, range = 1.0-1.5, n = 4) burrows per summer, and LTBs used consecutively by three of the four males within and/or among summers, were separated by 28.9 ± 21.5 m (range = 16.4-53.7 m, n = 3) (Fig. 5a, b, d). One male used the same burrow for three summers (Fig. 5c) and appeared to use the same burrow for the following two seasons (the burrow was occupied, but we could not determine for certain if it was the same male). Only one animal was known to return (after a period of 53 days) to a LTB (Fig. 5b). During winter, males with functional transmitters (n = 7) did not change position.
Chapter 1 Introduction
-Global decline of amphibians
-Conservation status of South African anurans
-Biology of Pyxicephalus adspersus
-Relevance and objectives of this thesis
Chapter 2 Spawning and non-breeding activity of adult giant bullfrogs (Pyxicephalus adspersus)
-Abstract
-Introduction
-Materials and Methods
-Results
-Discussion
-Tables
-Figures
Chapter 3 Conservation implications of spatial habitat use by adult giant bullfrogs (Pyxicephalus adspersus)
-Abstract
-Introduction
-Materials and Methods
-Results
-Discussion
-Tables
-Figures
Chapter 4 Conservation implications of the age/size distribution of giant bullfrogs (Pyxicephalus adspersus) at three peri-urban breeding sites
-Abstract
-Introduction
-Materials and Methods
-Results
-Discussion
-Tables
-Figures
Chapter 5 Conservation implications of giant bullfrog (Pyxicephalus adspersus) population genetic structure in Gauteng Province, South Africa
-Abstract
-Introduction
-Materials and Methods
-Results
-Discussion
-Tables
-Figures
Chapter 6 Conservation implications of habitat preference and geographic range of the giant bullfrog (Pyxicephalus adspersus) at two spatial scales
-Abstract
-Introduction
-Materials and Methods
-Results
-Discussion
-Tables
-Figures
Chapter 7 Conclusion
-Summary of results
-Concluding remarks
Literature Cited
