By the Ornate Burrowing Frog Platyplectrum Ornatum (Gray, 1842)
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Herpetology Notes, volume 8: 281-285 (2015) (published online on 18 May 2015) On the ant trail: “blitz-feeding” by the Ornate Burrowing Frog Platyplectrum ornatum (Gray, 1842) Matthew Mo Abstract. Little is known about the behaviour of many of Australia’s amphibians. In this paper, I report a series of incidental observations documenting “blitz-feeding” on ants and other arthropods by Ornate Burrowing Frogs (Platyplectrum ornatum) in the Pilliga forests and Bundarra, northern New South Wales, Australia. During these observations, frogs appeared to be strategically positioned on ant trails, crossing paths with 5–15 ants per minute. Frogs appeared to use their bodies to direct incoming ants towards their head. Blitz attacks were rapid, involving a volatile downward burst of the tongue. Similar behaviour has been confirmed in some Australian insectivorous lizards. Keywords. Australia, feeding strategy, insectivore, Limnodynastidae, Platyplectrum ornatum. Introduction be relatively small and cryptic (White, 1993), allowing them to become aware of the presence of observers Behaviours of Australian amphibians are generally before they can be observed undisturbed. poorly known. A substantial body of work on frog Platyplectrum ornatum (Limnodynastidae) is a ecology in Australia has focused on habitat selection, medium-sized foam-nesting frog (maximum SVL vocalisation, breeding, parasitology, and conservation 45 mm) found in northern and northeastern Australia status (e.g., Hazell, 2003; Goldingay and Newell, (Tyler and Knight, 2011; Cogger, 2014). A habitat 2005; Baker and Lauck, 2006; Daly and Craven, 2007; generalist, populations occur from a range of coastal Lemckert and Mahony, 2008; Lettoof et al., 2013). vegetation types to arid woodland in the drier interior Natural behaviour is difficult to directly observe in (Robinson, 1998). Distribution into dry environs frogs for a number of reasons. Most frogs are nocturnal is possible by retreating below ground in a state of and must be located at night by spotlighting; hence aestivation until adequate moisture becomes available the animals are disturbed at the time of detection. (Elkan, 1976; Withers, 1995). Platyplectrum ornatum Furthermore, frogs often retreat quickly or become apparently specialise in breeding in ephemeral pools motionless when approached, both responses that (Anstis, 2013; Kern et al., 2014). Ex-situ studies show doubtlessly alter natural behaviours. Even for frogs that its tadpoles readily prey on the eggs and tadpoles active and observable during the day, individuals may of other frogs (Crossland, 2000). Little more is known of its behaviour. This paper reports on observations of “blitz-feeding” on ants (order Hymenoptera) and other arthropods by P. platyplectrum recorded in the Pilliga forests and Bundarra in northern New South Wales Forest Science Centre, New South Wales Department of (NSW). Primary Industries, PO Box 242, Parramatta, New South Wales 2151, Australia Methods Current address: State Veterinary Diagnostic Laboratory, Elizabeth Macarthur Agricultural Institute, Woodbridge The Pilliga forests (30.83° S, 149.31° E) are the Road, Menangle, New South Wales 2568, Australia. Email: largest remaining continuous native forest section in [email protected] NSW west of the Great Dividing Range (Milledge, 282 Matthew Mo 2012). Two broad geological sections occur: flat, sandy outwash in the northwestern corner of the region and low rocky hills in the remainder. Typical vegetation is an association of White Cypress Pine (Callitris glaucophylla), Bull-oak (Allocasuarina luehmannii), and several Eucalyptus species, such as Blakely’s Red Gum (E. blakelyi), Narrow-leafed Ironbark (E. crebra), Pilliga Box (E. pilligaensis), and Poplar Box (E. populnea). The forests are a matrix of national parks and state forests, managed by the NSW National Parks and Wildlife Service and the Forestry Corporation of NSW, respectively. An extensive network of unsealed Figure 1. Video footage still showing an ant (arrow) roads provides easy public access. I visited the Pilliga moving close to the anterior of an Ornate Burrowing Frog forests during four one-week fieldtrips over a two-year (Platyplectrum ornatum), seconds before a feeding blitz. period. There was substantial rainfall prior to the first Notice the large eyes that bulge outward beyond the lips, visit in October 2012, and scattered precipitation prior to enabling the frog to see potential prey moving directly below two visits in November 2012 and March 2013. A fourth its head. visit was carried out in April 2014, after a severely dry summer. Bundarra (30.1667° S, 151.0667° E) is a small town located on the Great Dividing Range, 82 km northwest of Armidale and 130 km east of the Pilliga forests. Two three-day visits were conducted in January and June 2014. Frogs were encountered on private property and the Bundarra Cemetery. The terrain was a matrix of cleared paddock and open woodland dominated by Narrow- leafed Ironbark, New England Blackbutt (Eucalyptus andrewsii), and Roundleaf Gum (E. deanei). Platyplectrum ornatum were incidentally encountered on the roads at night. Their round body shape was relatively easy to detect by a focused observer in vehicle headlights. Spotlighting from a vehicle is a well- practiced method for locating terrestrial herpetofauna (Bishop et al., 1997; Kerr and Bull, 2004; Penman et Figure 2. Video footage still showing an Ornate Burrowing al., 2008). When a frog was located, the vehicle was Frog (Platyplectrum ornatum) lapping up its prey. stopped as far a distance as possible and observations were conducted using the headlights of the vehicle. Each time, the frog was located on an ant trail. In ten observations, the number of ants approaching within 5 cm of the frog’s anterior per minute was counted. Ten prey captures (between three individual Results frogs) were successfully timed with a stopwatch. For one A total of 32 and 23 P. ornatum were located on frog, feeding behaviour was recorded via photography. roads in the Pilliga forests and Bundarra, respectively. Obtaining images through still photography was Platyplectrum ornatum became motionless when extremely difficult due to the volatile action of the approached, sometimes tucking their limbs and feeding blitz. Failing this, the camera (Pentax Optio snouts against their bodies to reduce conspicuity. This WG-1) was set to video mode and placed in front of stationary response is similar to that observed in Eastern the frog. Frame rate was preset to 30 frames per second. Banjo Frogs (Limnodynastes dumerilii) and Sudell’s Still images were extracted during playback for this Frogs (Neobatrachus sudelli), which were also located paper (Figs. 1, 2). (Mo, 2014; Mo, unpubl. data). This was unlike the anti- On the ant trail: “blitz-feeding” by the Ornate Burrowing Frog 283 approached within 5 cm of the frogs’ anterior per minute (n = 10). Approaching ants followed the frog’s outline toward either the posterior or anterior (Fig. 1). Prey capture was apparently triggered by ants passing the front of the frog; carried out rapidly by a volatile downward burst of the tongue (Fig. 2). The time period taken to capture ants ranged between 0.3 and 0.5 seconds. Besides buccal pumping, no movement of the head was required prior to the capture. Large eyes that bulge out of the body appear to give P. ornatum the ability to sight prey that is immediately below its mouth. When capturing ants directly in front, a frog’s head movement was limited to lowering the lower jaw for protrusion of the tongue. When ants were positioned to the left or right of the head, the feeding blitz included a tilt of the head at the corresponding angle. This shows that frogs were targeting prey rather than striking opportunistically. As shown in Fig. 2, this behaviour involved a head tilt toward the right-hand side. All feeding blitzes observed resulted in the capture of prey, so that the feeding success rate was 100%. There did not appear to be any defensive actions or avoidance behaviours displayed by the ants. Apart from ants, there were two isolated observations of a wolf spider (family Lycosidae) and dragonfly (order Odonata) being consumed. The spider strayed close to a frog’s head (Fig. 3), prompting a feeding blitz. The capture occurred at a much slower speed than the actions described above. This enabled a series of still photographs to be recorded. These show that the spider was apparently stunned by the rapid onset of the feeding blitz before being consumed in at least four gulps. Similarly, the dragonfly, which hovered close to the frog, was maneuvered inside the mouth by a number of gulps. It landed near the frog’s head and was initially Figure 3. “Blitz-feeding” by an Ornate Burrowing Frog captured by the wing (Fig. 4). (Platyplectrum ornatum) on a Wolf Spider (family Lycosidae). Discussion Strategic positioning on ant trails is a known behaviour in other insectivorous herpetofauna, such the Thorny Devil, Moloch horridus (Pianka and Pianka, 1970; Clemente et al., 2004), Western Bearded Dragons, predator strategies of most other frogs seen, including Pogona minor (Thompson and Thompson, 2003), and Spotted Grass Frogs (Limnodynastes tasmaniensis), legless lizards, genus Aprasia (Webb and Shine, 1994). Desert Tree Frogs (Litoria rubella), or Broad-palmed While a single ant does not provide much nourishment, Rocket Frogs (L. latopalmata), which often hopped ants are abundant in inland Australia (Abensperg-Traun away. and Steven, 1997). By positioning itself in front of When located, P. ornatum appeared to be strategically an ant trail, a frog can eventually gather a substantial positioned on ant trails. Between five and 15 ants quantity over a period of time. 284 Matthew Mo comments by Hinrich Kaiser and an anonymous reviewer improved the manuscript. References Abensperg-Traun, M., Steven, D. (1997): Ant- and termite-eating in Australian mammals and lizards: a comparison. Australian Journal of Ecology 22: 9-17. Anstis, M. (2013): Tadpoles and Frogs of Australia. Sydney, New South Wales, Australia, New Holland Publishers.