Here is some latent information from a birder who previously conducted
scientific reasearch on Cane Toads and other frogs in North Qld. The toxic
parts of adult Cane Toads are the paratoid glands on the shoulders, the dorsal
skin and the ovaries. Quite a number of animals have learnt to eat the
non-toxic parts by flipping the toads and chomping through the underbelly.
Mostly they eat the internal organs (except the ovaries) and the thigh muscle
meat. In Townsville in the 1990s I recorded Aust White Ibis, Black Kites,
Australian Ravens and Water Rats doing this regularly. None however, left a
tiny hole in the throat, they sliced the belly wide open. All searched for
them systematically, apparently following the theory of search pattern
behaviour . At one point I had 24 open pens in a cow paddock by a dam, each
with a single adult and 10-30 tiny metamorphs (i.e. newly metamorphosed from
tadpoles). The adults started mysteriously disappearing
after a couple of days. Turned out that a flock of Ravens that had learnt to
check the pens at dawn each day, flip and kill the toads and then cache them in
trees. The sympatric Torresian Crows showed no interest in the Toads, but the
Ravens would defended my pens from their rival Crows all the same.
It does not surprise me that Night Herons also eat Cane Toads, and I'm sure
many other herons do too. However, I would be surprised if Night Herons did so
by making a small incision in the throat. They might be able to get the gut
that way, but not the heart or the thigh meat. I'm not sure what would eat them
that way, but suspect it might be something capable of crawling inside, a
centipede perhaps? Dissecting one of these victims might help.
Few things can eat a toad whole. A lot of snakes, goannas and quolls have
apparently died trying to do so. The widespread decline of these
preadators still puzzles me a little, because the Common Green Tree Frog is
just as toxic as the Cane Toad. These predators learn not to eat Green frogs,
but often don't learn to eat toads. Many of your listeners will know that their
puppies learn not to eat toads and green frogs alike after only lick of each,
but might be sick for a day or two afterwards (and then pretend not to notice
frogs for the rest of their lives). The Keelback, a common water snake that
specialises in eating frogs, eats the young metamorphs whole, and even seems to
prefer them to other frogs, at least sometimes. Meat Ants swarm and devour
small toads. Green Tree ants will carry flattened and dried road killed toads
in one piece up a tree to their nests in extrodrinary displays of
determination. A photo of a Papuan Frogmouth with a frog in
its bill was published on the back cover of wingspan maybe 15 years ago, with
the suggestion it may have been a Cane Toad, but who knows. In my pens, I
observed naive juvenile Pied Butcherbirds trying unsuccessfully to eat my
metamorph toads. They would pick them up and fiddle with them in their bills
but quickly drop them (alive and unharmed) and try another. I assume the small
parcel of edible meat wrapped in poisonous skin is too difficult to process,
unlike the adult toads.
The question is often asked by frog researchers "why are metamorph Cane
Toads diurnal when most other frogs are nocturnal?". They usually offer answers
like the night is too cold or some other reason why metamorphs are unable to be
active at night. I would suggest that they are able to be active by day when
most other frogs (including adult toads) cannot be, because they have better
defence against predatory diurnal birds.
Incidently, the tadpoles are very poionous too, and few predators can handle
them. This allows them to breed in water with fish, unlike native frogs. A
colleague was studying what did and did not eat the tadpoles, but so long ago I
can't recall much. Dragonfly larvae snip the tails off the taddies, which
leaves them to die floundering helplessly.
David James,
in Jakarta
==============================
________________________________
From: Del Richards <>
To:
Sent: Wednesday, 1 February 2012 11:54 AM
Subject: Roufous Night Heron dismembering Cane Toads.
Over some years I have had a programme "Bird Talk Back" on ABC Far North in
Cairns. Yesterday (31/01/2012) I fielded ten calls in thirty minutes.
Early in the programme a caller from Walkamin (between Mareeba and
Atherton) had found four dead cane toads with an small incision in their throat
by her small backyard pond.
I told her plainly that it was a good mystery thinking that it would be
animal attack rather than bird predation. About three calls later a gent from
Gordonvale south of Cairns assured us that he had watched White-tailed Rats and
(surprise, surprise!) Northern Brown Bandicoots kill and eat the non-toxic
underside parts of cane toads.
Minutes later the mystery was solved when George who owned a piggery at
Walkamin called in to tell us about Roufous Night Herons. He related that after
an early evening storm one time he checked the piggery and that a night heron
was moving through the pig pens and systematically flipping cane toads on their
back and taking out their innards.
Given the shape and dexterity of their pointed bill the night heron would
be well able to extract the gut through a small incision. On my next programme
I will endeavour to follow the thread on birds and cane toads in an effort to
derive some more latent information that is held out there by everyday
non-scientific observers.
Del. Richards, Fine Feather Tours, Mossman, NQ.
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