On the ant trail: “blitz-feeding” by the Ornate Burrowing Frog

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
Behaviours of Australian amphibians are generally
poorly known. A substantial body of work on frog
ecology in Australia has focused on habitat selection,
vocalisation, breeding, parasitology, and conservation
status (e.g., Hazell, 2003; Goldingay and Newell,
2005; Baker and Lauck, 2006; Daly and Craven, 2007;
Lemckert and Mahony, 2008; Lettoof et al., 2013).
Natural behaviour is difficult to directly observe in
frogs for a number of reasons. Most frogs are nocturnal
and must be located at night by spotlighting; hence
the animals are disturbed at the time of detection.
Furthermore, frogs often retreat quickly or become
motionless when approached, both responses that
doubtlessly alter natural behaviours. Even for frogs
active and observable during the day, individuals may
Forest Science Centre, New South Wales Department of
Primary Industries, PO Box 242, Parramatta, New South
Wales 2151, Australia
Current address: State Veterinary Diagnostic Laboratory,
Elizabeth Macarthur Agricultural Institute, Woodbridge
Road, Menangle, New South Wales 2568, Australia. Email:
[email protected]
be relatively small and cryptic (White, 1993), allowing
them to become aware of the presence of observers
before they can be observed undisturbed.
Platyplectrum ornatum (Limnodynastidae) is a
medium-sized foam-nesting frog (maximum SVL
45 mm) found in northern and northeastern Australia
(Tyler and Knight, 2011; Cogger, 2014). A habitat
generalist, populations occur from a range of coastal
vegetation types to arid woodland in the drier interior
(Robinson, 1998). Distribution into dry environs
is possible by retreating below ground in a state of
aestivation until adequate moisture becomes available
(Elkan, 1976; Withers, 1995). Platyplectrum ornatum
apparently specialise in breeding in ephemeral pools
(Anstis, 2013; Kern et al., 2014). Ex-situ studies show
that its tadpoles readily prey on the eggs and tadpoles
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
(NSW).
Methods
The Pilliga forests (30.83° S, 149.31° E) are the
largest remaining continuous native forest section in
NSW west of the Great Dividing Range (Milledge,
282
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
roads provides easy public access. I visited the Pilliga
forests during four one-week fieldtrips over a two-year
period. There was substantial rainfall prior to the first
visit in October 2012, and scattered precipitation prior to
two visits in November 2012 and March 2013. A fourth
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 Narrowleafed 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 wellpracticed method for locating terrestrial herpetofauna
(Bishop et al., 1997; Kerr and Bull, 2004; Penman et
al., 2008). When a frog was located, the vehicle was
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
frogs) were successfully timed with a stopwatch. For one
frog, feeding behaviour was recorded via photography.
Obtaining images through still photography was
extremely difficult due to the volatile action of the
feeding blitz. Failing this, the camera (Pentax Optio
WG-1) was set to video mode and placed in front of
the frog. Frame rate was preset to 30 frames per second.
Still images were extracted during playback for this
paper (Figs. 1, 2).
Matthew Mo
Figure 1. Video footage still showing an ant (arrow)
moving close to the anterior of an Ornate Burrowing Frog
(Platyplectrum ornatum), seconds before a feeding blitz.
Notice the large eyes that bulge outward beyond the lips,
enabling the frog to see potential prey moving directly below
its head.
Figure 2. Video footage still showing an Ornate Burrowing
Frog (Platyplectrum ornatum) lapping up its prey.
Results
A total of 32 and 23 P. ornatum were located on
roads in the Pilliga forests and Bundarra, respectively.
Platyplectrum ornatum became motionless when
approached, sometimes tucking their limbs and
snouts against their bodies to reduce conspicuity. This
stationary response is similar to that observed in Eastern
Banjo Frogs (Limnodynastes dumerilii) and Sudell’s
Frogs (Neobatrachus sudelli), which were also located
(Mo, 2014; Mo, unpubl. data). This was unlike the anti-
On the ant trail: “blitz-feeding” by the Ornate Burrowing Frog
Figure 3. “Blitz-feeding” by an Ornate Burrowing Frog
(Platyplectrum ornatum) on a Wolf Spider (family
Lycosidae).
predator strategies of most other frogs seen, including
Spotted Grass Frogs (Limnodynastes tasmaniensis),
Desert Tree Frogs (Litoria rubella), or Broad-palmed
Rocket Frogs (L. latopalmata), which often hopped
away.
When located, P. ornatum appeared to be strategically
positioned on ant trails. Between five and 15 ants
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
captured by the wing (Fig. 4).
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,
Pogona minor (Thompson and Thompson, 2003), and
legless lizards, genus Aprasia (Webb and Shine, 1994).
While a single ant does not provide much nourishment,
ants are abundant in inland Australia (Abensperg-Traun
and Steven, 1997). By positioning itself in front of
an ant trail, a frog can eventually gather a substantial
quantity over a period of time.
284
Matthew Mo
comments by Hinrich Kaiser and an anonymous reviewer
improved the manuscript.
References
Figure 4. Brief struggle following a feeding blitz by an Ornate
Burrowing Frog (Platyplectrum ornatum) on a dragonfly
(order Odonata).
Being on open ground may appear to expose P.
ornatum to predators (cf. Kyne and Jackson, 2013),
however two main defensive strategies were noticed
in observations in this paper. When approached, P.
ornatum may lower its head to the ground and tuck
its limbs tight against its body. In this posture, frogs
camouflage against the ground, especially in stony or
sandy terrain, and resemble a pebble. They may also
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Platyplectrum ornatum are abundant in the North West
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of a common species is a fair indication that there is
much more work to be done in this aspect of amphibian
ecology.
Acknowledgements. I thank Michael Murphy, Joel Hatch,
and the staff of the NSW National Parks and Wildlife Service
Baradine office for local support on my fieldtrips to the Pilliga
forests. Thanks also to Bruce, Donna, and Michael Mclean for
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Accepted by Hinrich Kaiser